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Internal Medicine

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Question 561Question →

A 3232-year-old primigravid woman at 3636 weeks gestation comes to the emergency department due to a one-week history of progressively worsening shortness of breath. She reports having to sleep propped up on three pillows and frequently waking up at night with a dry cough. Her medical history is notable for mild asthma during childhood and a 1010-pack-year smoking history, though she quit smoking upon becoming pregnant. Her temperature is 37.1∘C37.1^\circ\text{C} (98.8∘F98.8^\circ\text{F}), blood pressure is 112/76112/76 mm Hg, pulse is 114114/min, and respirations are 2424/min. Pulse oximetry shows 92%92\% on room air. Physical examination reveals distended neck veins with a jugular venous pressure of 1111 cm H 2_2 O. Cardiac auscultation demonstrates a regular tachycardia with a distinct third heart sound (S 3_3) gallop. Pulmonary examination shows fine crackles at the lung bases bilaterally. There is 2+2+ pitting edema extending to the mid-calves. An arterial blood gas analysis on room air shows a pH of 7.477.47, pCO 2_2 of 2929 mm Hg, and pO 2_2 of 6464 mm Hg. Which of the following is the most appropriate next step in the management of this patient?

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Answer: Perform a transthoracic echocardiogram

Answer

Perform a transthoracic echocardiogram
The correct answer is to perform a transthoracic echocardiogram. This patient presents with classic signs and symptoms of acute decompensated heart failure, likely secondary to peripartum cardiomyopathy given her gestational age. Key findings include orthopnea, paroxysmal nocturnal dyspnea (waking up at night with a dry cough), resting tachycardia, an S3 gallop, elevated jugular venous pressure, and pulmonary edema (crackles, hypoxemia). An echocardiogram is the essential next step to evaluate left ventricular systolic function, assess for wall motion abnormalities, and establish the diagnosis. The arterial blood gas demonstrates a primary respiratory alkalosis, which is a common physiologic change in pregnancy but here is exacerbated by hyperventilation from acute hypoxia.

Step-by-Step Solution

1
Analyze the patient's presenting symptoms and physical exam findings.
The patient exhibits orthopnea, paroxysmal nocturnal dyspnea, an S3 gallop, elevated JVP, and bibasilar crackles.
Identifying the constellation of signs and symptoms is necessary to differentiate between pulmonary and cardiovascular causes of dyspnea.
2
Distinguish between physiologic pregnancy changes and pathologic processes.
While mild peripheral edema and dyspnea can be normal in late pregnancy, an S3 gallop accompanied by elevated JVP and pulmonary crackles indicates pathologic acute decompensated heart failure.
Pregnancy involves significant hemodynamic changes that can mask or mimic disease, requiring careful differentiation.
3
Determine the diagnostic test of choice for suspected peripartum cardiomyopathy or new-onset heart failure.
A transthoracic echocardiogram is indicated to assess left ventricular ejection fraction and structural heart abnormalities.
Echocardiography is the gold standard, non-invasive imaging modality for diagnosing and characterizing heart failure.

Key Concept

Recognition and initial diagnostic evaluation of new-onset acute decompensated heart failure (e.g., peripartum cardiomyopathy) during pregnancy.
Question 562Question →

An otherwise healthy 55-year-old man arrives at the emergency department complaining of excruciating, generalized abdominal pain that began 2424 hours ago. The pain is accompanied by intractable nausea and multiple episodes of bilious vomiting. He reports no passage of stool or flatus since the symptoms started. His past surgical history is notable for an uncomplicated open appendectomy over a decade ago. Vital signs show a temperature of 38.6∘C38.6^\circ\text{C} (101.5∘F101.5^\circ\text{F}), a blood pressure of 98/6098/60 mm Hg, and a heart rate of 118118/min. Physical examination reveals a markedly distended and tympanic abdomen. There is diffuse, severe tenderness to palpation, accompanied by involuntary guarding and marked rebound tenderness. Bowel sounds are absent. Initial laboratory testing is significant for a leukocyte count of 18,500/mm318,500/\text{mm}^3 and a serum lactate concentration of 4.84.8 mmol/L. Upright abdominal radiography demonstrates multiple dilated loops of small intestine with prominent air-fluid levels and an absence of distal colonic gas. Which of the following is the most appropriate next step in the management of this patient?

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Answer: Immediate exploratory laparotomy

Answer

Immediate exploratory laparotomy
This patient presents with a mechanical small bowel obstruction (SBO) that is complicated by clear signs of bowel strangulation and ischemia. While his history of a prior appendectomy makes adhesive disease the most likely etiology, the critical aspect of this case is recognizing the severity of his condition. An uncomplicated SBO can often be managed conservatively with bowel rest and nasogastric decompression. However, this patient exhibits classic 'alarm' features of a complicated, strangulated obstruction: fever, tachycardia, hypotension, severe continuous pain, peritonitis (involuntary guarding and rebound tenderness), marked leukocytosis, and lactic acidosis. These findings indicate that the affected segment of the bowel has compromised blood flow and is becoming necrotic. The definitive and life-saving intervention for a strangulated SBO is an immediate exploratory laparotomy to resect any nonviable bowel and relieve the mechanical obstruction.

Step-by-Step Solution

1
Analyze the patient's presentation and imaging to establish the primary diagnosis.
The patient's obstipation, bilious vomiting, distension, prior abdominal surgery, and radiographic air-fluid levels confirm the diagnosis of an adhesive small bowel obstruction (SBO).
Identifying the mechanical obstruction is the prerequisite for determining the severity and necessary interventions.
2
Evaluate vital signs, physical examination findings, and laboratory values for severity criteria.
The presence of fever, tachycardia, involuntary guarding, rebound tenderness, leukocytosis, and elevated lactate indicate that the bowel is ischemic or strangulated.
Differentiating between uncomplicated and complicated SBO is critical, as it completely changes the management pathway.
3
Select the appropriate therapeutic intervention based on the complication status.
Immediate exploratory laparotomy is chosen.
A strangulated SBO is a surgical emergency. Delaying operative management leads to bowel necrosis, perforation, sepsis, and death.

Key Concept

Management of complicated (strangulated) small bowel obstruction
Question 563Question →

A 61-year-old female presents to the emergency department with a 2-day history of progressively worsening shortness of breath, orthopnea, and a nocturnal dry cough. Her past medical history includes hypertension, type 2 diabetes mellitus, and a myocardial infarction three years ago. She does not smoke. Her temperature is 37.1°C (98.8°F), blood pressure is 162/96 mmHg, pulse is 110/min, and respiratory rate is 28/min. Pulse oximetry shows 84% on room air. Physical examination reveals jugular venous distention. Lung auscultation demonstrates bilateral basilar crackles and scattered expiratory wheezes. A third heart sound (S3) is heard at the apex. There is trace bilateral pedal edema. Laboratory results show a leukocyte count of 7,800/mm³.

Arterial blood gas analysis on room air reveals:
- pH: 7.28
- PaCO2: 55 mmHg
- PaO2: 52 mmHg
- HCO3-: 25 mEq/L

Chest radiography shows an enlarged cardiac silhouette, bilateral perihilar alveolar opacities, and prominent interstitial markings. Which of the following are appropriate initial management steps for this patient? (Select all that apply)

Select all that apply

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Answer: Application of continuous positive airway pressure; Intravenous bolus of furosemide

Answer

The correct initial management steps include application of continuous positive airway pressure and administration of an intravenous bolus of furosemide.
The patient's clinical presentation—including orthopnea, elevated jugular venous pressure, an S3 gallop, and cardiomegaly with perihilar opacities—strongly indicates acute decompensated heart failure resulting in cardiogenic pulmonary edema. The presence of expiratory wheezing, often termed 'cardiac asthma', is due to peribronchial edema rather than primary bronchospasm. Initial management of acute pulmonary edema with severe respiratory distress requires immediate preload and afterload reduction. Application of continuous positive airway pressure (CPAP) reduces left ventricular preload by decreasing venous return, reduces afterload by decreasing transmural myocardial pressure, and recruits flooded alveoli to improve oxygenation. Simultaneously, an intravenous bolus of a loop diuretic (such as furosemide) acts rapidly as a venodilator to further reduce preload and subsequently promotes profound diuresis to clear total body fluid overload.

Step-by-Step Solution

1
Interpret the clinical presentation and physical examination findings.
The patient exhibits orthopnea, jugular venous distention, an S3 gallop, crackles, and wheezes (cardiac asthma), strongly indicating volume overload and left ventricular failure.
Establishing a primary diagnosis of acute decompensated heart failure is essential to differentiate the presentation from primary obstructive pulmonary diseases.
2
Analyze the arterial blood gas (ABG) results using physiological formulas.
The pH is 7.28 and PaCO2 is 55 mmHg. For acute respiratory acidosis, the expected pH change is a decrease of 0.08 for every 10 mmHg increase in PaCO2. Expected pH = 7.40−0.08×55−4010=7.287.40 - 0.08 \times \frac{55 - 40}{10} = 7.28. The measured pH precisely matches the expected pH.
Calculations confirm a simple acute respiratory acidosis driven by respiratory muscle fatigue and poor ventilation, effectively ruling out a concurrent metabolic acidosis.
3
Select appropriate interventions based on the definitive diagnosis of cardiogenic pulmonary edema with hypercapnic respiratory failure.
Diuresis (furosemide) and noninvasive positive pressure ventilation (CPAP) are selected to offload the left ventricle and rapidly improve oxygenation.
These dual therapies target the underlying pathophysiology of elevated hydrostatic pressure and alveolar fluid accumulation.

Key Concept

Acute decompensated heart failure presenting with hypercapnic respiratory failure requires diuresis and noninvasive positive pressure ventilation; the presence of wheezing ('cardiac asthma') should not lead to inappropriate administration of bronchodilators or corticosteroids.
Question 564Question →

A 34-year-old woman recently diagnosed with diffuse cutaneous systemic sclerosis presents for management of severe Raynaud phenomenon. Over the past month, she has experienced multiple daily episodes of triphasic color changes (pallor, cyanosis, erythema) in her fingers, accompanied by intense throbbing pain. She currently takes no medications. The physician discusses a stepwise treatment plan to reduce the frequency and severity of her vasospastic attacks, emphasizing that therapy will be escalated sequentially if her symptoms remain refractory to the prior intervention.

Arrange the following management steps in the correct guideline-recommended sequence of escalation, starting with the initial foundational intervention and ending with the rescue therapy reserved for refractory, critical digital ischemia.

Drag items to arrange them in the correct order

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Answer

The correct sequence for managing systemic sclerosis-associated Raynaud phenomenon is to begin with nonpharmacologic measures, progress to an oral dihydropyridine calcium channel blocker, escalate to a PDE-5 inhibitor if symptoms remain uncontrolled, and reserve intravenous prostanoids for critical, refractory ischemia.
The stepwise management of Raynaud phenomenon in systemic sclerosis is designed to balance vasodilatory efficacy against systemic side effects (primarily hypotension). Nonpharmacologic cold avoidance and smoking cessation form the foundation of therapy. When these fail, dihydropyridine calcium channel blockers (e.g., nifedipine, amlodipine) are the first-line pharmacologic agents. If symptoms persist despite maximal CCB therapy, stepping up to an oral PDE-5 inhibitor (e.g., sildenafil) is recommended. Finally, intravenous prostacyclin analogs (e.g., epoprostenol, iloprost) are the most potent vasodilators but are exclusively reserved for critical ischemia or active digital ulceration refractory to oral therapies due to their invasive route of administration and severe side-effect profile.

Step-by-Step Solution

1
Identify the foundational treatment for all patients with Raynaud phenomenon.
Nonpharmacologic measures (trigger avoidance, smoking cessation) are selected as the initial intervention.
Behavioral modifications can successfully control mild disease and carry no risk of systemic adverse effects like hypotension.
2
Determine the first-line pharmacologic therapy for patients requiring systemic treatment.
Oral dihydropyridine calcium channel blockers are selected as the second step.
CCBs are universally recommended as the safest and most effective initial oral vasodilators for primary and secondary Raynaud phenomenon.
3
Select the appropriate step-up pharmacologic agent for refractory symptoms.
Oral PDE-5 inhibitors are chosen as the third step.
When CCBs are insufficient or poorly tolerated at maximum doses, adding or substituting a PDE-5 inhibitor provides synergistic vasodilation.
4
Identify the definitive rescue therapy for critical ischemia.
Intravenous synthetic prostacyclin analogs are placed last in the sequence.
Due to the need for intravenous access, high cost, and severe systemic side effect profile, prostanoids are strictly reserved for impending gangrene or refractory active digital ulcers.

Key Concept

The management of secondary Raynaud phenomenon in systemic sclerosis follows a stepwise escalation: nonpharmacologic measures → oral calcium channel blockers → oral PDE-5 inhibitors or topical nitrates → intravenous prostanoids (for critical digital ischemia).
Question 565Question →

A 72-year-old woman is brought to the emergency department from a skilled nursing facility due to severe lethargy and altered mental status over the past 24 hours. Facility staff report she has had multiple episodes of voluminous, watery diarrhea for the past 3 days after completing a course of clindamycin for a cellulitis infection. Her medical history is significant for advanced chronic obstructive pulmonary disease (COPD) requiring home oxygen, hypertension, and heart failure with preserved ejection fraction.

Vital signs are:
Temperature: 37.8°C (100.0°F)
Heart rate: 112/min
Blood pressure: 90/60 mm Hg
Respiratory rate: 26/min
Oxygen saturation: 88% on her baseline 2 L/min nasal cannula.

Physical examination reveals dry mucous membranes and delayed capillary refill. Lung auscultation demonstrates diffusely decreased breath sounds with prolonged expiration and scattered end-expiratory wheezes. The patient is somnolent but arousable to physical stimuli.

Serum chemistry results are as follows:
Sodium: 135 mEq/L
Potassium: 3.1 mEq/L
Chloride: 110 mEq/L
Bicarbonate: 14 mEq/L
Blood urea nitrogen: 42 mg/dL
Creatinine: 1.6 mg/dL (baseline 0.9 mg/dL)

Arterial blood gas analysis (on 2 L/min oxygen) reveals:
pH: 7.19
PaCO2PaCO_2: 38 mm Hg
PaO2PaO_2: 58 mm Hg

Which of the following best characterizes this patient's current acid-base status?

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Answer: Normal anion gap metabolic acidosis and concurrent respiratory acidosis

Answer

Normal anion gap metabolic acidosis and concurrent respiratory acidosis
The correct answer identifies two simultaneous acid-base disorders. First, the patient's severe diarrhea has resulted in a profound loss of bicarbonate, leading to a metabolic acidosis. The anion gap is calculated as Na+−(Cl−+HCO3−)=135−(110+14)=11Na^+ - (Cl^- + HCO_3^-) = 135 - (110 + 14) = 11 mEq/L, which falls squarely into the normal range (8-12 mEq/L), confirming a normal anion gap metabolic acidosis (NAGMA). Second, to determine if the respiratory compensation is appropriate, Winter's formula must be applied: Expected PaCO2=(1.5×HCO3−)+8±2PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2. For this patient, Expected PaCO2=(1.5×14)+8=29±2PaCO_2 = (1.5 \times 14) + 8 = 29 \pm 2 mm Hg. The patient's actual measured PaCO2PaCO_2 is 38 mm Hg. Because the actual PaCO2PaCO_2 is significantly higher than the expected range of 27-31 mm Hg, the patient has a concurrent respiratory acidosis. This failure to adequately ventilate is highly consistent with impending respiratory failure in a patient with severe underlying COPD who is fatiguing under the stress of acute hypovolemic shock.

Step-by-Step Solution

1
Analyze the pH to determine the primary disturbance.
The pH is 7.19 (acidemia). The HCO3−HCO_3^- is 14 mEq/L (low) and the PaCO2PaCO_2 is 38 mm Hg (near normal). The primary disturbance is metabolic acidosis.
A low pH driven by a low bicarbonate indicates a primary metabolic acidosis.
2
Calculate the serum anion gap (AG).
AG = Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-) = 135−(110+14)=135−124=11135 - (110 + 14) = 135 - 124 = 11 mEq/L.
Determining the anion gap distinguishes between bicarbonate loss (normal AG, 8-12 mEq/L) and unmeasured acid accumulation (high AG, >12 mEq/L). The patient's diarrhea has caused a normal AG metabolic acidosis.
3
Calculate expected respiratory compensation using Winter's formula.
Expected PaCO2=(1.5×14)+8±2=21+8±2=29±2PaCO_2 = (1.5 \times 14) + 8 \pm 2 = 21 + 8 \pm 2 = 29 \pm 2 mm Hg (range 27-31 mm Hg).
This determines if the respiratory system is appropriately compensating for the metabolic acidosis.
4
Compare actual PaCO2PaCO_2 to expected PaCO2PaCO_2.
Actual PaCO2PaCO_2 (38 mm Hg) is greater than Expected PaCO2PaCO_2 (27-31 mm Hg).
Because the actual PaCO2PaCO_2 is higher than expected, there is inadequate ventilation, indicating a concurrent (superimposed) respiratory acidosis. This is likely due to diaphragmatic fatigue secondary to her underlying COPD and acute illness.

Key Concept

Acid-base analysis requires calculating the anion gap to categorize metabolic acidosis, followed by Winter's formula to uncover hidden secondary respiratory disorders; a 'normal' absolute PaCO2 value is highly abnormal in the setting of severe metabolic acidosis.
Question 566Question →

A 26-year-old woman, gravida 1, para 0, comes to the clinic at 9 weeks gestation for a routine prenatal visit. The patient reports mild morning nausea and breast tenderness but otherwise feels well. She has no history of thyroid disease and does not take any medications other than a standard prenatal vitamin. She reports no palpitations, tremors, heat intolerance, or weight loss. Vital signs are within normal limits. Physical examination reveals a normal-sized thyroid gland without palpable nodules, goiter, or bruits. Deep tendon reflexes are normal. Laboratory evaluation shows the following:

Laboratory TestResultReference Range
Hemoglobin11.5 g/dL11.0–15.0 g/dL
Thyroid-stimulating hormone (TSH)0.05 mU/L0.4–4.0 mU/L
Free thyroxine (Free T4)1.3 ng/dL0.9–1.7 ng/dL
Total thyroxine (Total T4)14.2 mcg/dL5.0–12.0 mcg/dL

Which of the following is the most appropriate next step in management?

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Answer: Reassurance and routine prenatal care

Answer

Reassurance and routine prenatal care
The correct management is reassurance and observation because the patient's laboratory results reflect normal physiologic adaptations to pregnancy. In the first trimester, high levels of human chorionic gonadotropin (hCG) can directly stimulate the TSH receptor due to structural similarities, resulting in increased thyroid hormone output and a compensatory suppression of TSH (gestational transient thyrotoxicosis). Concurrently, rising estrogen levels increase hepatic synthesis of thyroxine-binding globulin (TBG). This increases the body's pool of bound thyroid hormone, raising the Total T4. Crucially, the biologically active Free T4 level remains in the normal range, preventing clinical thyrotoxicosis. Because the patient lacks symptoms (e.g., palpitations, weight loss) and has normal free T4 levels, no medical intervention or further diagnostic workup is needed.

Step-by-Step Solution

1
Evaluate the clinical presentation.
The patient is completely asymptomatic aside from normal early-pregnancy nausea. She has no physical signs of thyrotoxicosis (e.g., tachycardia, tremor, goiter).
Differentiating between pathologic hyperthyroidism (which requires treatment) and physiologic changes of pregnancy (which do not) relies heavily on the presence or absence of clinical symptoms.
2
Interpret the thyroid laboratory panel in the context of pregnancy.
The patient has a suppressed TSH, elevated Total T4, but a normal Free T4.
During the first trimester, elevated hCG shares a structural subunit with TSH and weakly stimulates the TSH receptor, leading to increased endogenous thyroid hormone production and a compensatory drop in TSH (gestational transient thyrotoxicosis). Concurrently, increased estrogen stimulates hepatic production of thyroxine-binding globulin (TBG), which binds circulating thyroid hormone, raising Total T4 levels while biologically active Free T4 remains normal.
3
Determine the appropriate management.
Observation and routine prenatal care.
Because the free T4 remains within normal limits and the patient is asymptomatic, these findings confirm normal physiologic adaptations to pregnancy. No antithyroid medications or further diagnostic testing is required.

Key Concept

Normal physiologic changes of thyroid function in pregnancy include an estrogen-induced increase in TBG (elevating total T4) and an hCG-induced weak stimulation of the TSH receptor (suppressing TSH), while free T4 remains essentially normal.
Question 567Question →

A 38-year-old man is brought to the emergency department by his partner due to a 2-week history of progressively worsening headaches, nausea, and confusion. He was diagnosed with HIV infection 5 years ago but has been nonadherent to his antiretroviral therapy for the past 2 years. His temperature is 38.2°C (100.8°F), blood pressure is 118/76 mm Hg, and pulse is 92/min. Physical examination shows lethargy and bilateral papilledema, but no focal motor weakness or sensory deficits. Laboratory studies show a CD4 T-lymphocyte count of 34 cells/mm³.

A CT scan of the head shows no mass effect, hemorrhage, or hydrocephalus. A lumbar puncture is performed with an opening pressure of 340 mm H2O340 \text{ mm H}_2\text{O}. Cerebrospinal fluid (CSF) analysis reveals:
Leukocyte count: 45/mm³ (85% lymphocytes)
Glucose: 30 mg/dL
Protein: 95 mg/dL
CSF cryptococcal antigen is positive.

He is admitted to the hospital and immediately started on intravenous liposomal amphotericin B and oral flucytosine. Four days later, his partner reports that the patient is significantly more difficult to arouse and has been complaining of severe blurred vision. His temperature is 37.6°C (99.7°F). Neurologic examination shows a sluggish pupillary light reflex bilaterally and worsening papilledema. Which of the following is the most appropriate next step in management?

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Answer: Perform a therapeutic lumbar puncture

Answer

Perform a therapeutic lumbar puncture
This patient with advanced HIV has cryptococcal meningitis, which is being appropriately treated with induction therapy (liposomal amphotericin B and flucytosine). However, he has developed worsening lethargy, visual changes, and papilledema, which strongly suggest acutely elevated intracranial pressure (ICP). Elevated ICP in cryptococcal meningitis is thought to be caused by the mechanical obstruction of cerebrospinal fluid (CSF) outflow at the arachnoid villi by the shedding of the cryptococcal polysaccharide capsule. The definitive, first-line management for symptomatic elevated ICP in these patients is mechanical drainage of CSF via therapeutic lumbar puncture (often performed serially on a daily basis) to a target closing pressure of <200 mm H2O< 200 \text{ mm H}_2\text{O} or 50%50\% of the opening pressure. Medications that reduce ICP in other settings (e.g., mannitol, acetazolamide) are ineffective here, and corticosteroids are strictly contraindicated.

Step-by-Step Solution

1
Identify the primary diagnosis and current complication.
The patient has HIV with cryptococcal meningitis (positive CSF antigen, low CD4) and is now presenting with signs of worsening elevated intracranial pressure (lethargy, blurred vision, sluggish pupils, worsening papilledema) on day 4 of induction therapy.
Recognizing the complication is essential for selecting the appropriate management, as elevated ICP is a major cause of morbidity and mortality in cryptococcal meningitis.
2
Determine the optimal intervention for elevated ICP in cryptococcal meningitis.
The first-line intervention for symptomatic elevated ICP in this setting is mechanical removal of CSF via therapeutic lumbar punctures to a target closing pressure of < 200 mm H2O or 50% of the opening pressure.
Cryptococcal capsular polysaccharide physically obstructs CSF outflow at the arachnoid villi. Medical management (e.g., mannitol, acetazolamide, or steroids) is ineffective and potentially harmful.
3
Rule out alternative interventions.
Steroids are contraindicated, ART must be delayed to prevent IRIS, switching to fluconazole is premature, and VP shunting is reserved for refractory cases after serial LPs fail.
This confirms that a therapeutic lumbar puncture is the single best next step in management.

Key Concept

Elevated intracranial pressure is a common, life-threatening complication of cryptococcal meningitis that should be managed initially with serial therapeutic lumbar punctures rather than medical therapy (e.g., steroids) or immediate surgical shunting.
Question 568Question →

A 68-year-old woman is brought to the emergency department by her son due to progressive lethargy and confusion over the past 24 hours. The son reports that she has experienced severe, watery diarrhea and intractable vomiting for the last 4 days following a suspected foodborne illness. Her past medical history is significant for severe chronic obstructive pulmonary disease (COPD) requiring home oxygen therapy. Upon arrival, her temperature is 37.1∘37.1^\circ C (98.8∘98.8^\circ F), blood pressure is 82/5082/50 mmHg, heart rate is 124124/min, and respiratory rate is 2828/min. Physical examination reveals a somnolent patient with profoundly dry mucous membranes, decreased skin turgor, and diffuse bilateral wheezing.

Laboratory studies reveal:

TestResult
Sodium140140 mEq/L
Potassium3.13.1 mEq/L
Chloride8686 mEq/L
Bicarbonate1414 mEq/L
Blood urea nitrogen6262 mg/dL
Serum creatinine2.82.8 mg/dL
Albumin4.04.0 g/dL
Lactate7.47.4 mmol/L

An arterial blood gas obtained on room air shows:

ParameterResult
pH7.117.11
PaCO2_24545 mmHg
PaO2_25858 mmHg

Which of the following combinations most accurately characterizes this patient's acid-base status?

Show answer & explanation

Answer: High anion gap metabolic acidosis, metabolic alkalosis, and respiratory acidosis

Answer

The patient's acid-base status is best characterized by a high anion gap metabolic acidosis, a metabolic alkalosis, and a respiratory acidosis.
The correct combination characterizes a classic triple acid-base disorder. First, the anion gap is 4040 mEq/L (140−(86+14)140 - (86 + 14)), diagnosing a high anion gap metabolic acidosis (HAGMA) secondary to lactic acidosis from shock. Second, calculating the delta gap (40−12=2840 - 12 = 28) and adding it to the measured bicarbonate (14+28=4214 + 28 = 42) yields an expected bicarbonate greater than 2424 mEq/L, confirming a concurrent metabolic alkalosis (from intractable vomiting). Finally, Winter's formula predicts a PaCO 2_2 of 27−3127-31 mmHg. The measured PaCO 2_2 of 4545 mmHg is inappropriately high, confirming a superimposed respiratory acidosis due to COPD exacerbation and respiratory muscle fatigue.

Step-by-Step Solution

1
Analyze the primary disturbance.
The pH is 7.117.11 (acidemia) and the HCO 3−_3^- is 1414 mEq/L (low). This indicates a primary metabolic acidosis.
Identifying the primary direction of pH and matching it with the appropriate buffer system change establishes the baseline disorder.
2
Calculate the anion gap (AG).
AG = Na +^+ - (Cl −^- + HCO 3−_3^-) = 140−(86+14)=40140 - (86 + 14) = 40 mEq/L. Since 4040 > 1212, a high anion gap metabolic acidosis (HAGMA) is present.
An elevated anion gap confirms the presence of unmeasured anions, in this case, lactate due to tissue hypoperfusion.
3
Calculate the delta gap (Δ\Delta AG) and expected bicarbonate.
Δ\Delta AG = 40−12=2840 - 12 = 28 mEq/L. The patient's expected HCO 3−_3^- (if HAGMA were the only metabolic disorder) is: Measured HCO 3−_3^- + Δ\Delta AG = 14+28=4214 + 28 = 42 mEq/L. Since 4242 is significantly greater than a normal HCO 3−_3^- of 2424, a concurrent metabolic alkalosis is present.
The delta-delta ratio or expected bicarbonate calculation uncovers hidden metabolic disorders. In this patient, vomiting induced a severe metabolic alkalosis that partially masked the severity of the bicarbonate drop from the HAGMA.
4
Calculate expected respiratory compensation using Winter's formula.
Expected PaCO 2_2 = (1.5×14)+8=29±2(1.5 \times 14) + 8 = 29 \pm 2 mmHg. The measured PaCO 2_2 is 4545 mmHg.
Winter's formula determines if the respiratory response to metabolic acidosis is adequate. Since the measured PaCO 2_2 (4545 mmHg) is higher than the expected range (27−3127-31 mmHg), there is an uncompensated accumulation of CO 2_2, indicating a superimposed respiratory acidosis.

Key Concept

Diagnosis of a triple acid-base disorder requires sequential calculation of the anion gap, the delta-delta gap (or expected bicarbonate), and Winter's formula.
Estimated Time:3m 0s
Question 569Question →

A 2727-year-old man presents to the urgent care clinic complaining of diffuse abdominal pain, nausea, and extreme thirst that began yesterday. He acknowledges missing several doses of his prescribed long-acting insulin. On physical examination, his respiratory rate is 28/min28/\text{min} with deep, labored breathing. A distinct fruity odor is noted on his breath. Laboratory results are as follows:

Serum sodium: 138 mEq/L138 \text{ mEq/L}
Serum chloride: 100 mEq/L100 \text{ mEq/L}
Serum bicarbonate: 10 mEq/L10 \text{ mEq/L}

Arterial blood gas (room air):
pH: 7.227.22
pCO2pCO_2: 23 mm Hg23 \text{ mm Hg}
pO2pO_2: 96 mm Hg96 \text{ mm Hg}

Based on the provided laboratory values, which of the following is the most accurate interpretation of this patient's acid-base status?

Show answer & explanation

Answer: Fully compensated high anion gap metabolic acidosis

Answer

Fully compensated high anion gap metabolic acidosis
The correct interpretation is a fully compensated high anion gap metabolic acidosis. The patient's low pH (7.227.22) and low bicarbonate (10 mEq/L10 \text{ mEq/L}) demonstrate a metabolic acidosis. The anion gap is elevated at 28 mEq/L28 \text{ mEq/L}. To determine if the respiratory compensation is adequate, Winter's formula (Expected pCO2=1.5×[HCO3−]+8±2Expected\ pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2) is applied. In this case, (1.5×10)+8=23 mm Hg(1.5 \times 10) + 8 = 23 \text{ mm Hg}. Because the measured pCO2pCO_2 (23 mm Hg23 \text{ mm Hg}) falls exactly within the expected range, the patient is fully compensated and does not have a secondary acid-base disturbance.

Step-by-Step Solution

1
Determine the primary disorder from the pH and bicarbonate.
pH is 7.227.22 (acidemia) and HCO3−HCO_3^- is 10 mEq/L10 \text{ mEq/L} (low), confirming a primary metabolic acidosis.
Establishing the initial direction of the pH and the primary driver is the first step in acid-base analysis.
2
Calculate the anion gap to classify the metabolic acidosis.
AG=Na+−(Cl−+HCO3−)=138−(100+10)=28 mEq/LAG = Na^+ - (Cl^- + HCO_3^-) = 138 - (100 + 10) = 28 \text{ mEq/L}. The normal range is 8−12 mEq/L8-12 \text{ mEq/L}, so this is a high anion gap metabolic acidosis.
Metabolic acidosis must be categorized into normal or high anion gap to narrow the differential diagnosis (e.g., DKA in this patient).
3
Use Winter's formula to assess if respiratory compensation is appropriate.
Expected pCO2=1.5×[HCO3−]+8±2pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2. Thus, Expected pCO2=(1.5×10)+8=15+8=23±2pCO_2 = (1.5 \times 10) + 8 = 15 + 8 = 23 \pm 2 (range 21−25 mm Hg21-25 \text{ mm Hg}).
If the measured pCO2pCO_2 falls outside the expected range, a secondary respiratory disorder is present.
4
Compare expected and measured pCO2pCO_2.
The measured pCO2pCO_2 is 23 mm Hg23 \text{ mm Hg}, which perfectly matches the expected value.
This confirms there is no concurrent respiratory acidosis or alkalosis, meaning the condition is a simple, fully compensated high anion gap metabolic acidosis.

Key Concept

In patients with metabolic acidosis, the primary disorder must be classified using the anion gap, and appropriate respiratory compensation must be verified using Winter's formula to rule out mixed acid-base disorders.
Estimated Time:1m 0s
Question 570Question →

A 46-year-old man presents to the clinic with persistent blood pressure elevation despite adherence to a regimen of amlodipine, lisinopril, and hydrochlorothiazide. His blood pressure today is 168/102 mm Hg. A basic metabolic panel reveals a serum potassium level of 2.8 mEq/L and a serum bicarbonate level of 31 mEq/L. The physician suspects primary aldosteronism and transitions his antihypertensive regimen to verapamil and doxazosin to prepare for diagnostic testing. Arrange the following steps in the most appropriate sequential order for the definitive evaluation and management of this patient's condition.

Drag items to arrange them in the correct order

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Answer

The correct sequence is: 1) Measure plasma aldosterone concentration and plasma renin activity, 2) Perform an intravenous saline infusion test, 3) Obtain a high-resolution CT scan of the abdomen, 4) Perform adrenal venous sampling, 5) Proceed with unilateral laparoscopic adrenalectomy.
The evaluation of primary aldosteronism requires a highly disciplined, stepwise algorithmic approach. Initial screening is performed using a plasma aldosterone-to-renin ratio. Because the ARR serves only as a screening tool, positive results must be biochemically confirmed with a suppression test (such as an intravenous saline load or oral sodium loading) to definitively prove autonomous aldosterone production. Once confirmed, a high-resolution CT scan of the abdomen is obtained to anatomically evaluate the adrenal glands and, crucially, rule out adrenocortical carcinoma. However, in patients older than 35, CT is anatomically suggestive but functionally insufficient due to the high population prevalence of non-functioning adrenal incidentalomas. Therefore, adrenal venous sampling (AVS) is the gold standard and must be performed to confirm unilateral hypersecretion before proceeding to definitive treatment with unilateral adrenalectomy.

Step-by-Step Solution

1
Screen for hyperaldosteronism using the aldosterone-to-renin ratio (ARR).
An elevated ARR (typically >20) with high aldosterone and suppressed renin indicates possible primary aldosteronism.
Screening is the most sensitive initial test to identify at-risk patients among those with resistant hypertension and hypokalemia.
2
Confirm the diagnosis with an intravenous saline infusion test or oral sodium load.
Failure to suppress aldosterone levels to normal following a sodium load confirms autonomous aldosterone production.
Biochemical confirmation is mandatory before proceeding to anatomic imaging, as the screening ARR can yield false positives.
3
Perform a high-resolution adrenal CT scan.
Identifies the presence of adrenal masses (such as adenomas or carcinomas) or bilateral glandular enlargement (hyperplasia).
Imaging localizes the pathology and rules out large malignant tumors, guiding further invasive functional testing.
4
Perform adrenal venous sampling (AVS).
Confirms lateralization of aldosterone hypersecretion to one specific adrenal gland.
In patients >35 years old, CT findings can be misleading due to the frequency of non-functioning incidentalomas. AVS is the gold standard to prove unilateral disease.
5
Refer the patient for unilateral adrenalectomy.
Surgical removal of the hypersecreting adrenal gland.
This provides definitive curative management for confirmed unilateral primary aldosteronism.

Key Concept

The diagnostic algorithm for primary aldosteronism requires a strict stepwise progression: biochemical screening (ARR), biochemical confirmation (suppression testing), anatomical localization (CT), functional lateralization (adrenal venous sampling), and finally, definitive surgical or medical management.
Question 571Question →

Match each clinical presentation to the highly specific autoantibody most closely associated with the underlying diagnosis.

Click a left item, then click its matching right item

Items

A patient with new-onset skin thickening proximal to the elbows, accompanied by bibasilar pulmonary crackles.
A patient presenting with puffy hands, severe Raynaud phenomenon, and clinical features overlapping lupus and myositis.
A patient treated for a cardiac arrhythmia who develops polyarthritis and pleuritis, without evident renal or neurologic disease.
A patient with chronic otitis media, recurrent epistaxis, nasal septal perforation, and active glomerulonephritis.

Matches

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Answer

Diffuse systemic sclerosis pairs with anti-topoisomerase I; mixed connective tissue disease pairs with anti-U1 RNP; drug-induced lupus pairs with anti-histone; and granulomatosis with polyangiitis pairs with anti-proteinase 3.
Each clinical scenario contains pathognomonic features that point to a distinct rheumatologic or vasculitic diagnosis. Matching them correctly requires knowing the specific autoantibody profile that confirms each disease.

Step-by-Step Solution

1
Analyze the first clinical presentation regarding proximal skin thickening and lung crackles.
Identified as diffuse systemic sclerosis.
This establishes the need to pair it with anti-topoisomerase I (anti-Scl-70), its specific serologic marker.
2
Evaluate the second presentation involving puffy hands and overlapping connective tissue features.
Recognized as mixed connective tissue disease (MCTD).
MCTD is defined serologically by the presence of anti-U1 RNP antibodies.
3
Assess the third patient taking an anti-arrhythmic medication who developed mild lupus-like symptoms.
Diagnosed as drug-induced lupus.
Drug-induced lupus is classically associated with anti-histone antibodies, unlike systemic lupus erythematosus which features anti-dsDNA.
4
Review the final vignette detailing upper airway destruction and renal disease.
Identified as granulomatosis with polyangiitis (GPA).
GPA is a small-vessel vasculitis strongly linked to c-ANCA (anti-proteinase 3) antibodies.

Key Concept

Serologic Autoantibodies in Rheumatologic Diseases
Question 572Question →

A 62-year-old man is evaluated on the general medical ward on his third day of hospitalization. He was initially admitted for fever, right-sided flank pain, and leukocytosis. Blood and urine cultures were drawn, and he was started on empirical intravenous piperacillin-tazobactam for suspected complicated pyelonephritis. His past medical history is notable for benign prostatic hyperplasia and diet-controlled type 2 diabetes mellitus.

The patient has been afebrile for the past 24 hours, and his flank pain has largely resolved. He is currently kept strictly nil per os (NPO) in preparation for an elective esophagogastroduodenoscopy (EGD) scheduled in 2 hours to evaluate chronic dyspepsia.

Both the admission blood and urine cultures are now positive for *Klebsiella pneumoniae*. The susceptibility report for the isolate is as follows:

Ampicillin: Resistant
Cefazolin: Susceptible
Ceftazidime: Susceptible
Ceftriaxone: Susceptible
Ciprofloxacin: Susceptible
Meropenem: Susceptible
Piperacillin-tazobactam: Susceptible

Which of the following is the most appropriate next step in the patient's pharmacologic management?

Show answer & explanation

Answer: Switch to intravenous cefazolin

Answer

The most appropriate next step is to switch the patient's antibiotic to intravenous cefazolin.
The correct answer is to switch to intravenous cefazolin. This patient is clinically improving on empirical broad-spectrum therapy for complicated pyelonephritis and bacteremia. With culture results showing a pansensitive *Klebsiella pneumoniae* isolate, standard antibiotic stewardship principles dictate de-escalating to the narrowest-spectrum effective agent. Cefazolin, a first-generation cephalosporin, is highly effective for susceptible Enterobacteriaceae and has a much narrower spectrum than piperacillin-tazobactam, thereby reducing the risk of collateral damage. Because the patient is strictly NPO for an impending EGD, an intravenous formulation is required at this time, making IV cefazolin the ideal choice.

Step-by-Step Solution

1
Evaluate the patient's clinical trajectory and current regimen.
The patient is clinically stable, afebrile, and improving on empirical piperacillin-tazobactam therapy.
Clinical stability indicates that stepping down or de-escalating therapy can be safely considered once definitive pathogen data is available.
2
Analyze the culture and susceptibility results to identify de-escalation options.
The pathogen is Klebsiella pneumoniae, which is susceptible to multiple narrow and broad-spectrum agents, including cefazolin.
Identifying the susceptibility profile allows the clinician to discontinue overly broad empirical agents.
3
Select the most appropriate targeted therapy based on spectrum and patient-specific constraints.
Intravenous cefazolin is chosen.
Cefazolin is the narrowest-spectrum effective agent available, minimizing collateral damage. The intravenous route is required because the patient is strictly NPO for a procedure in 2 hours.

Key Concept

Antibiotic stewardship requires de-escalating from empirical broad-spectrum therapy to the narrowest-spectrum effective agent once culture and susceptibility data are available, while accounting for patient-specific constraints such as NPO status.
Question 573Question →

An internal medicine team is reviewing the culture data for a patient admitted to the hospital 4848 hours ago for septic shock secondary to a complicated urinary tract infection. The patient, who has a history of benign prostatic hyperplasia, initially presented with marked hypotension, flank pain, and a temperature of 39.4∘C39.4^\circ\text{C} (102.9∘F102.9^\circ\text{F}). He was aggressively resuscitated with intravenous crystalloids and started on broad-spectrum empiric therapy with intravenous piperacillin-tazobactam.

He is now hemodynamically stable, has been afebrile for the past 1212 hours, and his leukocytosis is resolving. He is currently unable to take medications by mouth due to severe postoperative nausea and vomiting from a recent, unrelated orthopedic procedure.

Final culture results from both blood and urine demonstrate the presence of *Escherichia coli*. The isolate's susceptibility report is as follows:

* Ampicillin: Resistant
* Trimethoprim-sulfamethoxazole: Resistant
* Ceftriaxone: Susceptible
* Cefepime: Susceptible
* Piperacillin-tazobactam: Susceptible
* Meropenem: Susceptible

Based on the principles of antimicrobial stewardship, which of the following is the most appropriate next step in pharmacotherapy?

Show answer & explanation

Answer: Transition to intravenous ceftriaxone

Answer

The most appropriate step is to transition the patient to intravenous ceftriaxone.
The correct action is transitioning to intravenous ceftriaxone. A core tenet of antimicrobial stewardship is de-escalation: once a specific pathogen and its susceptibility profile are identified, empiric broad-spectrum antimicrobial therapy should be narrowed to the most targeted agent available. This patient has Escherichia coli bacteremia and pyelonephritis that is highly susceptible to ceftriaxone. Ceftriaxone effectively treats the infection while sparing broader spectrum agents like piperacillin-tazobactam, cefepime, and meropenem, all of which possess unnecessary anti-pseudomonal and/or broader anaerobic activity that the patient does not need. Because the patient cannot take oral medications due to severe nausea, a step-down to an oral agent (which would otherwise be preferred) is contraindicated, making intravenous ceftriaxone the ideal definitive choice.

Step-by-Step Solution

1
Interpret the clinical status and definitive culture results.
The patient is clinically stable, and cultures have identified Escherichia coli that is susceptible to multiple beta-lactam antibiotics.
Evaluating clinical trajectory alongside definitive microbiologic data is required before modifying an empiric antimicrobial regimen.
2
Apply the principles of antimicrobial stewardship.
De-escalation from empiric broad-spectrum therapy (piperacillin-tazobactam) to the most targeted, narrow-spectrum effective agent is indicated.
De-escalation minimizes the risk of antimicrobial resistance, collateral damage to the microbiome, and adverse drug effects.
3
Select the optimal targeted therapeutic agent based on the antibiogram.
Intravenous ceftriaxone is selected as the definitive therapy.
Ceftriaxone effectively targets the susceptible isolate without providing unnecessary anti-pseudomonal or broad anaerobic coverage. An intravenous route is necessary due to the patient's inability to tolerate oral intake.

Key Concept

Antimicrobial Stewardship and De-escalation
Question 574Question →

Match each classic clinical presentation of an endocrine disorder to the most appropriate initial diagnostic screening test.

Click a left item, then click its matching right item

Items

52-year-old man with an enlarged jaw, coarse facial features, and recently increased shoe size
28-year-old woman with progressive weight gain, proximal muscle weakness, and wide purple abdominal striae
44-year-old man with treatment-resistant hypertension and unprovoked hypokalemia
31-year-old woman with episodic headaches, severe diaphoresis, and sudden-onset tachycardia

Matches

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Answer

Acromegaly matches with IGF-1; Cushing syndrome matches with the overnight low-dose dexamethasone suppression test; primary hyperaldosteronism matches with the aldosterone-to-renin ratio; and pheochromocytoma matches with plasma free metanephrines.
Each clinical presentation describes a distinct hyperfunctioning endocrine state that requires a specific initial biochemical screening test. Acromegaly (growth hormone excess) is screened with IGF-1. Cushing syndrome (cortisol excess) is screened with a low-dose dexamethasone suppression test. Primary hyperaldosteronism (mineralocorticoid excess) is screened with an aldosterone-to-renin ratio. Pheochromocytoma (catecholamine excess) is screened with plasma free metanephrines.

Step-by-Step Solution

1
Identify the underlying endocrine syndrome for each clinical presentation.
Patient 1 has acromegaly, Patient 2 has Cushing syndrome, Patient 3 has primary hyperaldosteronism, and Patient 4 has pheochromocytoma.
Recognizing the correct syndrome is necessary to select the appropriate biochemical screening test.
2
Determine the most sensitive initial screening test for each identified disorder.
Acromegaly requires IGF-1; Cushing requires hypercortisolism demonstration (dexamethasone suppression); primary hyperaldosteronism requires aldosterone/renin ratio; pheochromocytoma requires metanephrines.
Initial endocrine workups rely on highly sensitive screening tests before confirmatory testing or imaging is pursued.

Key Concept

Initial diagnostic screening tests for classic adrenal and pituitary hypersecretory syndromes.
Question 575Question →

Evaluate the following inpatient scenarios involving patients currently receiving antimicrobial therapy. Match each clinical situation to the most appropriate stewardship-aligned modification to their regimen.

Click a left item, then click its matching right item

Items

A 70-year-old woman admitted with pyelonephritis and bacteremia, initially treated with empiric piperacillin-tazobactam. Cultures grow pan-susceptible Escherichia coli. She remains strictly NPO due to severe nausea.
A 65-year-old man admitted for an acute exacerbation of chronic obstructive pulmonary disease (COPD), initially started on levofloxacin. On hospital day 2, his respiratory viral panel is positive for Influenza A, and his serum procalcitonin level is 0.04 ng/mL.
A 55-year-old man recovering from ventilator-associated pneumonia has received 8 days of appropriately targeted cefepime. He has been afebrile for 72 hours with normalized inflammatory markers and stable respiratory status.
A 40-year-old woman with community-acquired pneumonia initially treated with intravenous ceftriaxone and azithromycin. She is now afebrile, eating well, and her urinary pneumococcal antigen test returns positive.

Matches

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Answer

The correct matches align specific stewardship principles to each scenario: de-escalating to narrow-spectrum intravenous therapy when oral intake is contraindicated, discontinuing antibiotics when a viral etiology is confirmed, adhering to evidence-based 7-day treatment durations for VAP, and transitioning to narrow-spectrum oral therapy when a patient demonstrates clinical stability.
Each correct pairing reflects a core pillar of antimicrobial stewardship: (1) tailoring therapy to the narrowest spectrum agent based on culture results, (2) stopping antibiotics when biomarkers and viral panels suggest an alternative etiology, (3) restricting therapy to guideline-recommended durations to limit toxicity, and (4) transitioning to oral agents to reduce hospital length of stay and line-associated complications once clinical stability is achieved.

Step-by-Step Solution

1
Evaluate the indication and route for the patient with E. coli bacteremia.
She requires continued intravenous therapy due to being NPO, but the spectrum should be narrowed to ceftriaxone.
Piperacillin-tazobactam provides unnecessary pseudomonal and anaerobic coverage for pan-susceptible E. coli, violating stewardship principles.
2
Assess the COPD patient's laboratory results.
Antibiotics should be stopped and antivirals started.
A low procalcitonin level and positive influenza test confirm a viral etiology without bacterial superinfection.
3
Determine the appropriate duration of therapy for the patient with VAP.
Discontinue all antibiotics immediately.
Evidence-based guidelines recommend a maximum 7-day course for VAP in a clinically improving patient; day 8 represents completed therapy.
4
Evaluate the clinical status and diagnostic data for the patient with CAP.
Switch to oral amoxicillin.
She is clinically stable, tolerating PO intake, and has a confirmed Streptococcus pneumoniae infection, allowing safe step-down to a targeted oral beta-lactam.

Key Concept

Antimicrobial stewardship involves optimizing patient outcomes while minimizing resistance by de-escalating to the narrowest effective agent, converting from intravenous to oral routes upon clinical stability, limiting treatment to evidence-based durations, and discontinuing antibiotics when non-bacterial etiologies are identified.
Question 576Question →

A 42-year-old woman comes to the clinic for evaluation of profound fatigue, weakness, and a 5-kg (11-lb) weight gain over the last 4 months. She also reports cold intolerance and that she has not had a menstrual period for the past 6 months. Her past medical history is unremarkable. She takes no medications. Blood pressure is 110/70 mm Hg, pulse is 52/min, and respirations are 12/min. Physical examination shows a puffy face, dry skin, and delayed relaxation of deep tendon reflexes. The thyroid gland is not palpable. Visual field testing reveals decreased peripheral vision bilaterally.

Laboratory studies show:
TestResultNormal Range
Sodium135 mEq/L136–145 mEq/L
Potassium4.0 mEq/L3.5–5.0 mEq/L
Thyroid-stimulating hormone (TSH)1.1 µU/mL0.4–4.0 µU/mL
Free thyroxine (T4)0.5 ng/dL0.9–1.7 ng/dL

Which of the following is the most appropriate next step in the management of this patient?

Show answer & explanation

Answer: Measure serum morning cortisol level

Answer

Measure serum morning cortisol level
This patient presents with classic signs and symptoms of hypothyroidism (fatigue, weight gain, cold intolerance, delayed deep tendon reflexes, bradycardia). Laboratory testing confirms a low free T4. In primary hypothyroidism, the lack of negative feedback leads to a significantly elevated TSH. In this patient, however, the TSH is inappropriately normal, which is the hallmark of central (secondary) hypothyroidism. The presence of amenorrhea and bitemporal hemianopsia (decreased peripheral vision bilaterally) strongly points to a compressive pituitary macroadenoma causing panhypopituitarism. Because the anterior pituitary also produces ACTH, patients with central hypothyroidism frequently have coexisting central adrenal insufficiency. The administration of thyroid hormone increases the metabolic clearance of cortisol. If levothyroxine is given to a patient with untreated adrenal insufficiency, it can rapidly precipitate an acute, life-threatening adrenal crisis. Therefore, the most critical next step is to measure the serum morning cortisol level to evaluate the adrenal axis. An MRI of the brain is also indicated to evaluate the pituitary mass.

Step-by-Step Solution

1
Analyze the clinical presentation and laboratory results.
The patient has symptoms of hypothyroidism (fatigue, weight gain, bradycardia) confirmed by a low free T4. However, the TSH is inappropriately normal, pointing to central (secondary) hypothyroidism rather than a primary thyroid disorder.
Differentiating primary from central hypothyroidism is crucial for determining the underlying etiology and directing further workup.
2
Identify clues indicating a broader syndrome.
The patient also has amenorrhea (suggesting hypogonadotropic hypogonadism) and bitemporal hemianopsia (decreased peripheral vision), which strongly suggest a compressive pituitary macroadenoma causing panhypopituitarism.
A mass compressing the optic chiasm and pituitary stalk affects multiple anterior pituitary axes.
3
Determine the safest next step in management.
Evaluate the adrenal axis by measuring the serum morning cortisol level before starting levothyroxine.
Patients with panhypopituitarism often have concomitant central adrenal insufficiency. Thyroid hormone increases the metabolic clearance of cortisol; therefore, giving levothyroxine without first ruling out or treating adrenal insufficiency can precipitate an acute adrenal crisis.

Key Concept

In patients with central hypothyroidism, the adrenal axis must be evaluated (and treated if deficient) prior to initiating levothyroxine therapy to avoid precipitating an acute adrenal crisis.
Question 577Question →

Microscopic examination of urine sediment is a critical diagnostic tool in evaluating renal pathology. Match each classic urinary cast finding with its most likely associated underlying pathophysiology or clinical condition.

Click a left item, then click its matching right item

Items

Red blood cell casts
Muddy brown granular casts
White blood cell casts
Fatty casts and oval fat bodies

Matches

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Answer

Red blood cell casts match with Glomerular inflammation (Glomerulonephritis). Muddy brown granular casts match with Ischemic or toxic tubular injury (Acute tubular necrosis). White blood cell casts match with Tubulointerstitial inflammation (Acute interstitial nephritis). Fatty casts match with Heavy proteinuria and altered lipid metabolism (Nephrotic syndrome).
Each urinary cast has a specific mechanism of formation that points to the underlying renal pathology. Red blood cell casts signify glomerular inflammation. Muddy brown granular casts denote necrotic tubular injury. White blood cell casts reflect tubulointerstitial inflammation. Fatty casts occur when severe proteinuria causes compensatory hyperlipidemia, leading to lipiduria.

Step-by-Step Solution

1
Identify the etiology of red blood cell casts.
RBC casts form when red blood cells leak through a damaged glomerular basement membrane and get trapped in Tamm-Horsfall mucoprotein in the tubules.
Understanding the origin of RBC casts links them directly to glomerulonephritis.
2
Identify the etiology of muddy brown granular casts.
These casts are made of necrotic epithelial cells from the renal tubules.
This pathophysiologic mechanism characterizes acute tubular necrosis (ATN).
3
Identify the etiology of white blood cell casts.
WBCs enter the tubules during severe interstitial inflammation or infection.
This links WBC casts to acute interstitial nephritis (AIN) or pyelonephritis.
4
Identify the etiology of fatty casts.
Heavy proteinuria in nephrotic syndrome triggers hepatic lipoprotein synthesis, leading to lipiduria and fatty cast formation.
This mechanism connects fatty casts directly to nephrotic syndrome.

Key Concept

Interpretation of urinary casts is essential for differentiating the causes of acute kidney injury and intrinsic renal disease.
Question 578Question →

A 72-year-old man is hospitalized due to 3 weeks of progressive fatigue, low-grade fevers, and shortness of breath with exertion. Six weeks ago, he underwent a transurethral resection of the prostate for benign prostatic hyperplasia. On physical examination, his temperature is 38.2°C (100.8°F), pulse is 94/min, blood pressure is 132/84 mm Hg, and respirations are 18/min. Cardiac auscultation reveals a new grade 3/6 holosystolic murmur loudest at the apex with radiation to the axilla. Examination of the extremities shows splinter hemorrhages under the fingernails of both hands.

Laboratory studies show:
Leukocyte count: 14,500/mm³
Hemoglobin: 10.8 g/dL
Platelets: 130,000/mm³
Blood urea nitrogen: 42 mg/dL
Serum creatinine: 2.1 mg/dL (baseline 1.1 mg/dL)

Transesophageal echocardiography demonstrates a 1.4-cm oscillating vegetation on the anterior leaflet of the mitral valve with moderate-to-severe mitral regurgitation. Empiric therapy with intravenous vancomycin and gentamicin is initiated. Two days later, three sets of blood cultures drawn prior to antibiotic administration are positive for *Enterococcus faecalis*. Antimicrobial susceptibility testing indicates the isolate is susceptible to ampicillin, penicillin, and vancomycin, and exhibits no high-level resistance to gentamicin. The patient remains hemodynamically stable.

Which of the following is the most appropriate next step in the pharmacologic management of this patient?

Show answer & explanation

Answer: Switch to intravenous ampicillin and ceftriaxone

Answer

The most appropriate next step is to switch to intravenous ampicillin and ceftriaxone, which provides required synergistic bactericidal activity without worsening the patient's acute kidney injury.
The correct answer is to switch to intravenous ampicillin and ceftriaxone. This patient has *Enterococcus faecalis* infective endocarditis, likely arising from his recent transurethral resection of the prostate (a classic risk factor due to genitourinary instrumentation). Enterococci are intrinsically tolerant to beta-lactam antibiotics because their primary penicillin-binding proteins (PBPs) have a low affinity for them. Therefore, cell wall synthesis inhibitors (like ampicillin) are merely bacteriostatic against Enterococci when used alone. To achieve the bactericidal activity necessary to cure endocarditis and sterilize the cardiac vegetations, synergistic combination therapy must be used.

Historically, the standard of care was ampicillin combined with an aminoglycoside (gentamicin). However, gentamicin is highly nephrotoxic. This patient has developed an acute kidney injury (serum creatinine increased from 1.1 mg/dL to 2.1 mg/dL). In patients with impaired renal function, the combination of ampicillin and ceftriaxone is the definitively preferred regimen. Ceftriaxone saturates specific PBPs (PBP2 and PBP3) that ampicillin does not effectively target, forcing the bacteria to rely on PBP5, which is then overwhelmed by ampicillin. This dual-beta-lactam therapy provides excellent bactericidal synergy against *E. faecalis* without the severe risk of aminoglycoside-induced nephrotoxicity.

Step-by-Step Solution

1
Identify the patient's primary diagnosis and the causative organism.
The patient has native valve infective endocarditis caused by Enterococcus faecalis, likely secondary to his recent genitourinary procedure.
Establishing the diagnosis and microbiologic etiology dictates the required duration and type of antimicrobial therapy.
2
Determine the required properties of antimicrobial therapy for this condition.
Infective endocarditis requires prolonged, bactericidal therapy to sterilize avascular heart valve vegetations. For Enterococcus, beta-lactam monotherapy is only bacteriostatic.
Enterococci are inherently tolerant to beta-lactams due to low-affinity penicillin-binding proteins (PBPs), so combination therapy is required to achieve a bactericidal effect.
3
Evaluate the patient's clinical status to select the safest synergistic regimen.
The patient has an acute kidney injury (creatinine 2.1 mg/dL, elevated from baseline). Therefore, the traditional synergistic agent, gentamicin (an aminoglycoside), is contraindicated due to its nephrotoxicity.
Ceftriaxone, when combined with ampicillin, provides excellent synergistic bactericidal activity against E. faecalis and avoids nephrotoxicity, making it the regimen of choice.

Key Concept

For Enterococcus faecalis infective endocarditis, the combination of ampicillin and ceftriaxone provides synergistic bactericidal activity and is the preferred regimen for patients with, or at high risk for, nephrotoxicity.
Question 579Question →

A 4848-year-old man is evaluated for resistant hypertension. His blood pressure is 168/104 mm Hg168/104 \text{ mm Hg} despite strict adherence to maximum-dose amlodipine, lisinopril, and hydrochlorothiazide. He reports recent episodes of muscle cramping and significant fatigue. Laboratory studies reveal a serum potassium level of 2.9 mEq/L2.9 \text{ mEq/L} and a serum sodium level of 146 mEq/L146 \text{ mEq/L}. The physician suspects a specific endocrine etiology for his secondary hypertension. Arrange the following diagnostic and management steps in the most appropriate chronological sequence for this patient.

Drag items to arrange them in the correct order

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Answer

The correct sequence is: (1) Screening with plasma aldosterone-to-renin ratio, (2) Confirmatory saline suppression test, (3) Anatomical localization with adrenal CT, (4) Functional confirmation with adrenal venous sampling, and (5) Definitive treatment with unilateral adrenalectomy.
The diagnostic workup of primary hyperaldosteronism strictly follows a protocol designed to prevent the surgical removal of nonfunctioning adrenal incidentalomas. The cascade requires biochemical screening (aldosterone-to-renin ratio) to detect potential cases. Positive screens require biochemical confirmation (saline suppression test) to prove autonomy. Once confirmed, anatomical localization (CT scan) identifies structural abnormalities. However, because incidentalomas are highly prevalent in patients older than 3535, structural abnormalities must undergo functional lateralization (adrenal venous sampling) to prove the visible nodule is actively secreting aldosterone. Only after AVS lateralizes the hypersecretion to one gland is unilateral adrenalectomy indicated. If AVS shows bilateral hypersecretion, the patient is treated medically with mineralocorticoid receptor antagonists (e.g., spironolactone).

Step-by-Step Solution

1
Perform initial biochemical screening for primary hyperaldosteronism.
Obtain an early-morning plasma aldosterone concentration (PAC) and plasma renin activity (PRA).
Patients with resistant hypertension accompanied by spontaneous or diuretic-induced hypokalemia have a high pretest probability for primary hyperaldosteronism and require a screening PAC/PRA ratio.
2
Confirm autonomous aldosterone secretion.
Perform a suppression test, such as the intravenous saline infusion test.
The PAC/PRA ratio is highly sensitive but can yield false positives. A confirmatory test demonstrating the failure of aldosterone to suppress under volume expansion proves autonomous secretion.
3
Anatomically localize the suspected lesion.
Obtain a high-resolution CT scan of the abdomen.
Imaging distinguishes between bilateral adrenal hyperplasia, a unilateral adenoma, and rarer conditions like adrenocortical carcinoma. It must follow, not precede, biochemical confirmation.
4
Confirm functional lateralization of the hormone hypersecretion.
Perform bilateral adrenal venous sampling (AVS).
Because nonfunctioning adrenal adenomas (incidentalomas) are found in up to 10%10\% of patients over age 4040, AVS is required to prove that the radiologically identified nodule is the actual source of aldosterone before removing the gland.
5
Provide definitive treatment for the identified pathology.
Proceed with unilateral laparoscopic adrenalectomy.
Surgery is the definitive cure for a biochemically active, functionally lateralized unilateral aldosterone-producing adenoma.

Key Concept

The precise, stepwise diagnostic and management algorithm for primary hyperaldosteronism.
Question 580Question →

A 28-year-old woman is brought to the emergency department by her husband due to a 1-week history of worsening fatigue, facial rash, and shortness of breath that is exacerbated by deep inspiration. She was diagnosed with systemic lupus erythematosus (SLE) 4 years ago but stopped taking her prescribed mycophenolate mofetil and hydroxychloroquine 8 months ago. Her temperature is 38.6°C (101.5°F), blood pressure is 155/95 mmHg, heart rate is 110/min, and respiratory rate is 24/min. Physical examination reveals an erythematous rash across her cheeks and nasal bridge that spares the nasolabial folds. Lung auscultation demonstrates decreased breath sounds at the bilateral bases and a pleural friction rub. Mild jugular venous distention is present.

Laboratory studies show:
Laboratory TestResultReference Range
Hemoglobin9.2 g/dL12.0–16.0 g/dL
Leukocyte count2,800/mm³4,500–11,000/mm³
Platelet count95,000/mm³150,000–400,000/mm³
Blood urea nitrogen42 mg/dL7–18 mg/dL
Serum creatinine2.4 mg/dL0.6–1.2 mg/dL
Thyroid-stimulating hormone (TSH)1.1 mU/L0.5–5.0 mU/L
Free T40.7 ng/dL0.9–1.7 ng/dL
Arterial blood gas analysis on room air reveals:
Arterial Blood GasResultReference Range
pH7.287.35–7.45
pCO2pCO_226 mmHg35–45 mmHg
pO2pO_288 mmHg75–105 mmHg
HCO3−HCO_3^-12 mEq/L22–28 mEq/L

Urinalysis shows 3+ protein, 20-30 red blood cells/hpf, and red blood cell casts. A urine culture obtained on admission grows >100,000 CFU/mL of *Escherichia coli* that is sensitive to amoxicillin, ceftriaxone, and nitrofurantoin. Blood cultures are pending.

Which of the following is the most appropriate next step in management?

Show answer & explanation

Answer: Initiate high-dose intravenous methylprednisolone

Answer

Initiate high-dose intravenous methylprednisolone
The patient is experiencing a severe, organ-threatening flare of systemic lupus erythematosus (SLE), characterized by proliferative lupus nephritis (acute kidney injury, proteinuria, red blood cell casts), serositis (pleuritic chest pain, friction rub, pleural effusions), and hematologic involvement (pancytopenia). The most appropriate next step in managing an acute, life-threatening SLE flare is the administration of high-dose intravenous glucocorticoids (e.g., methylprednisolone). Once the acute inflammation is controlled, a steroid-sparing immunosuppressant (e.g., cyclophosphamide or mycophenolate mofetil) will be initiated for induction therapy.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and history.
The patient has a history of nonadherence to SLE medications and presents with a malar rash, pancytopenia, acute kidney injury with RBC casts (lupus nephritis), and pleurisy with effusions (serositis).
Identifying the underlying disease process is required to select the correct targeted therapy.
2
Evaluate the arterial blood gas using Winter's formula to determine if there is a mixed acid-base disorder.
Expected pCO2=(1.5×12)+8±2=26±2pCO_2 = (1.5 \times 12) + 8 \pm 2 = 26 \pm 2 mmHg. The patient's actual pCO2pCO_2 is 26 mmHg, indicating adequate respiratory compensation for the metabolic acidosis.
This rules out a secondary respiratory acidosis and confirms sodium bicarbonate is not urgently indicated for uncompensated respiratory failure.
3
Interpret the thyroid function tests and urine culture in the context of critical illness.
The low free T4 with a normal TSH in an acutely ill patient indicates euthyroid sick syndrome. The *E. coli* UTI is sensitive to narrow-spectrum agents.
This rules out the need for levothyroxine and broad-spectrum antibiotics like meropenem.
4
Determine the definitive treatment for the primary pathology.
The patient is experiencing a severe, organ-threatening SLE flare, requiring immediate administration of high-dose intravenous corticosteroids.
Without rapid immunosuppression, the proliferative lupus nephritis and pancytopenia will worsen and potentially become fatal.

Key Concept

Severe, organ-threatening flares of Systemic Lupus Erythematosus (such as proliferative lupus nephritis or severe serositis) require immediate treatment with high-dose intravenous glucocorticoids.
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Internal Medicine Practice Questions — USMLE Step 2 CK — Page 29 | Examkin