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Question 561Question →

A 6060-year-old woman is brought to the emergency department by her husband due to progressive confusion, profound fatigue, and generalized weakness over the past week. Two weeks ago, she had a mild upper respiratory infection. Her husband notes she has been complaining of intermittent headaches and peripheral vision loss for the last three months. Her temperature is 36.2∘C36.2^\circ\text{C} (97.2∘F97.2^\circ\text{F}), blood pressure is 82/50 mm Hg82/50\text{ mm Hg}, pulse is 54/min54/\text{min}, and respirations are 16/min16/\text{min}. Physical examination shows a lethargic woman with dry, pale skin and delayed relaxation of deep tendon reflexes. Mild bilateral non-pitting lower extremity edema is present. Lung auscultation reveals decreased breath sounds at the bases but no crackles or wheezes.

Laboratory evaluation shows:

ParameterValue
Sodium128 mEq/L128\text{ mEq/L}
Potassium4.2 mEq/L4.2\text{ mEq/L}
Chloride98 mEq/L98\text{ mEq/L}
Bicarbonate20 mEq/L20\text{ mEq/L}
Blood urea nitrogen24 mg/dL24\text{ mg/dL}
Creatinine1.1 mg/dL1.1\text{ mg/dL}
pH7.327.32
PaCO2\text{PaCO}_238 mm Hg38\text{ mm Hg}
PaO2\text{PaO}_285 mm Hg85\text{ mm Hg}
Thyroid-stimulating hormone (TSH)0.8 \muU/mL0.8\text{ \mu U/mL} (Normal: 0.4−4.0 \muU/mL0.4-4.0\text{ \mu U/mL})
Free thyroxine (T4\text{T}_4)0.3 ng/dL0.3\text{ ng/dL} (Normal: 0.9−1.7 ng/dL0.9-1.7\text{ ng/dL})

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

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Answer: Administration of intravenous hydrocortisone

Answer

Administration of intravenous hydrocortisone
This patient's presentation of headaches, peripheral vision loss, profound fatigue, bradycardia, and non-pitting edema is highly suspicious for a pituitary macroadenoma causing panhypopituitarism. The laboratory findings of a low free T4\text{T}_4 coupled with an inappropriately normal TSH confirm central (secondary) hypothyroidism. The patient is currently presenting with hemodynamic collapse (hypotension, altered mental status) and hyponatremia, triggered by the physiological stress of a recent viral infection. This is the classic presentation of an acute adrenal crisis due to secondary adrenal insufficiency (ACTH deficiency). Notably, in secondary adrenal insufficiency, aldosterone production is preserved via the renin-angiotensin-aldosterone system, which is why her serum potassium level is normal despite the severe hyponatremia (caused by loss of cortisol's suppressive effect on ADH). In cases of suspected adrenal crisis, immediate administration of intravenous glucocorticoids (such as hydrocortisone) is life-saving and is the most critical next step. Glucocorticoids must always be replaced before thyroid hormone.

Step-by-Step Solution

1
Evaluate the clinical presentation for underlying etiology.
The combination of headaches, peripheral vision loss (bitemporal hemianopsia), and signs of hypothyroidism suggests a pituitary macroadenoma.
Mass effect from a pituitary tumor commonly compresses the optic chiasm and disrupts normal anterior pituitary hormone secretion.
2
Interpret the thyroid function tests.
The free T4\text{T}_4 is low while the TSH is inappropriately normal, indicating central (secondary) hypothyroidism.
In primary hypothyroidism, the TSH would be significantly elevated. A normal or low TSH in the presence of low T4\text{T}_4 implies pituitary or hypothalamic failure.
3
Analyze the acute hemodynamic collapse.
The patient is experiencing hypotension, altered mental status, and hyponatremia triggered by a recent infection, representing an acute adrenal crisis.
A pituitary mass causing central hypothyroidism likely also causes secondary adrenal insufficiency (ACTH deficiency), which decompensates under physiological stress.
4
Determine the safest and most critical initial treatment.
Intravenous hydrocortisone must be administered immediately.
Glucocorticoids must be replaced before thyroid hormone, because thyroid hormone increases the metabolic clearance of cortisol and can precipitate a fatal adrenal crisis if given alone.

Key Concept

In patients with suspected panhypopituitarism presenting in acute decompensation, immediate intravenous glucocorticoid replacement is required to treat secondary adrenal crisis before initiating thyroid hormone replacement.
Question 562Question →

A 62-year-old man is evaluated in the hospital on hospital day 3. He was initially admitted for fever, chills, and a warm, swollen right calf. On admission, his temperature was 39.1 C (102.4 F), blood pressure was 105/65 mm Hg, and pulse was 110/min. He was started on empiric intravenous vancomycin and piperacillin-tazobactam. Today, his temperature is 37.4 C (99.3 F), blood pressure is 120/75 mm Hg, and pulse is 82/min. The erythema on his right calf has significantly decreased. Blood cultures drawn on admission are positive for Staphylococcus aureus in 2 of 2 bottles. Susceptibility testing shows the isolate is resistant to penicillin but susceptible to oxacillin, cefazolin, and vancomycin. The patient has no history of medication allergies. Which of the following is the most appropriate next step in management?

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Answer: Switch to intravenous cefazolin

Answer

Switch to intravenous cefazolin
The patient has methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. For MSSA bacteremia, targeted beta-lactams such as first-generation cephalosporins (e.g., cefazolin) or anti-staphylococcal penicillins (e.g., nafcillin, oxacillin) are the treatments of choice. They have been consistently shown to be superior to vancomycin for MSSA infections, resulting in faster bacterial clearance, lower rates of clinical failure, and reduced mortality. Because the isolate is susceptible and the patient has no beta-lactam allergies, de-escalating to cefazolin is the most appropriate next step.

Step-by-Step Solution

1
Analyze the blood culture and susceptibility results.
The pathogen is identified as methicillin-susceptible Staphylococcus aureus (MSSA) because it is susceptible to oxacillin and cefazolin.
Identifying the specific susceptibility pattern is required to transition from empiric to targeted, definitive therapy.
2
Evaluate the patient's current empiric antibiotic regimen against the culture data.
The current regimen of vancomycin and piperacillin-tazobactam is overly broad and suboptimal for MSSA.
Vancomycin covers MRSA but is inferior to beta-lactams for MSSA. Piperacillin-tazobactam covers Pseudomonas and anaerobes, which are not present in this patient's cultures.
3
Select the most appropriate definitive therapy based on antimicrobial stewardship principles.
Intravenous cefazolin should be initiated.
Cefazolin (or an anti-staphylococcal penicillin like nafcillin) provides targeted, narrow-spectrum coverage and has proven superiority over vancomycin for MSSA bacteremia.

Key Concept

Methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia should be treated with a narrow-spectrum beta-lactam (e.g., cefazolin, nafcillin, or oxacillin) rather than vancomycin due to superior clinical outcomes.
Question 563Question →

Match each classic clinical presentation of an infectious disease with its most appropriate first-line pharmacotherapy.

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Items

A 26-year-old man with a painless, indurated genital ulcer and non-tender inguinal lymphadenopathy
A 32-year-old woman with an expanding, targetoid erythematous rash on her leg following a tick bite
A 12-year-old boy with acute onset of fever, tonsillar exudates, and tender anterior cervical adenopathy without a cough
A 19-year-old athlete with a painful, fluctuant, purulent skin abscess on his leg requiring drainage

Matches

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Answer

The presentations map to their respective first-line therapies: primary syphilis with benzathine penicillin G, early Lyme disease with doxycycline, streptococcal pharyngitis with amoxicillin, and community-acquired MRSA with trimethoprim-sulfamethoxazole.
Each clinical vignette provides pathognomonic or highly specific features for a common infection, which precisely corresponds to a well-established, guideline-directed first-line antimicrobial agent.

Step-by-Step Solution

1
Diagnose the infectious disease described in each clinical vignette based on classic signs and symptoms.
The vignettes sequentially describe primary syphilis, early localized Lyme disease, group A streptococcal pharyngitis, and a community-acquired MRSA skin abscess.
Accurate clinical pattern recognition is the necessary first step before selecting empiric antimicrobial therapy.
2
Identify the guideline-recommended, first-line antimicrobial agent for each diagnosed condition.
Primary syphilis requires benzathine penicillin G; Lyme disease requires doxycycline; Streptococcal pharyngitis requires amoxicillin; CA-MRSA requires trimethoprim-sulfamethoxazole.
Using targeted, first-line therapy ensures clinical efficacy while adhering to antimicrobial stewardship principles by avoiding unnecessarily broad coverage.

Key Concept

Empiric antimicrobial selection for common outpatient infectious diseases based on classic clinical presentations.
Question 564Question →

Match each patient's clinical presentation with the most likely corresponding urinalysis sediment finding.

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Items

A 62-year-old man who develops acute kidney injury 48 hours after prolonged hypotension during an emergency abdominal aortic aneurysm repair.
A 24-year-old woman with recent onset of a malar rash, photosensitivity, and new hematuria with mild renal insufficiency.
A 45-year-old man presenting with severe generalized edema, a serum albumin of 2.1 g/dL, and a 24-hour urine protein excretion of 5.2 g.
A 58-year-old woman presenting with high fever, right-sided costovertebral angle tenderness, dysuria, and acute kidney injury.
A 72-year-old man with longstanding, poorly controlled hypertension and diabetes mellitus, presenting with small, echogenic kidneys on ultrasound.

Matches

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Answer

The correct matches pair acute tubular necrosis with muddy brown casts, glomerulonephritis with red blood cell casts, nephrotic syndrome with fatty casts, acute pyelonephritis with white blood cell casts, and advanced chronic kidney disease with broad waxy casts.
Each clinical vignette presents classic hallmark features for a distinct renal pathology. The underlying mechanism of injury directly dictates the type of cells or substances that precipitate within the renal tubules to form casts: necrotic epithelial cells (ATN), red blood cells (glomerulonephritis), lipids (nephrotic syndrome), neutrophils (pyelonephritis), or degenerate proteins in dilated tubules (advanced CKD).

Step-by-Step Solution

1
Analyze the first patient's presentation involving hypotension and surgery.
Identify ischemia-induced acute tubular necrosis (ATN).
ATN is the most common cause of intrinsic acute kidney injury following severe hypoperfusion.
2
Evaluate the second patient's systemic symptoms and hematuria.
Identify acute glomerulonephritis, likely secondary to systemic lupus erythematosus.
Glomerular inflammation leads to the passage of red blood cells through the damaged basement membrane.
3
Assess the third patient's severe edema, hypoalbuminemia, and massive proteinuria.
Identify nephrotic syndrome.
Proteinuria greater than 3.5 g/day defines nephrotic syndrome, which profoundly alters lipid metabolism.
4
Examine the fourth patient's fever and costovertebral angle tenderness.
Identify acute pyelonephritis.
These are hallmark signs of an upper urinary tract infection involving the renal interstitium.
5
Review the fifth patient's chronic comorbidities and small kidneys on ultrasound.
Identify advanced chronic kidney disease (CKD).
Chronic irreversible scarring leads to loss of renal mass and compensatory hypertrophy of remaining tubules.

Key Concept

Urinalysis sediment and cast differentiation in renal disease
Estimated Time:2m 0s
Question 565Question →

Match each classic physical examination finding to the endocrine condition with which it is most commonly associated.

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Items

Pretibial myxedema (non-pitting edema of the lower extremities)
Facial muscle spasm upon tapping the cheek (Chvostek sign)
Violaceous abdominal striae greater than 1 cm in width
Hyperpigmentation of the palmar creases and oral mucosa

Matches

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Answer

Pretibial myxedema pairs with Graves disease; the Chvostek sign pairs with Hypocalcemia; violaceous abdominal striae pair with Cushing syndrome; and hyperpigmentation pairs with Primary adrenal insufficiency.
Each physical finding is highly specific to its respective endocrine disorder's underlying pathophysiology. Pretibial myxedema is a localized autoimmune phenomenon unique to Graves disease. The Chvostek sign reflects the classic neuromuscular excitability seen in hypocalcemia. Violaceous striae arise from hypercortisolism-induced catabolism in Cushing syndrome. Diffuse hyperpigmentation is a direct result of elevated ACTH/MSH seen specifically in primary adrenal insufficiency.

Step-by-Step Solution

1
Analyze the dermatologic finding of pretibial myxedema.
Identify it as a unique autoimmune manifestation.
It is mediated by TSH receptor antibodies stimulating dermal fibroblasts, uniquely linking it to Graves disease.
2
Evaluate the neuromuscular finding (Chvostek sign).
Identify it as a sign of membrane instability.
Low extracellular calcium directly increases the resting membrane potential of nerves, causing twitching upon mechanical stimulation.
3
Assess the origin of wide, violaceous striae.
Identify it as a sign of connective tissue breakdown.
Excess glucocorticoids (Cushing syndrome) weaken collagen and cause skin thinning, exposing underlying vascular beds.
4
Determine the cause of mucosal and palmar hyperpigmentation.
Identify it as a sign of elevated pro-opiomelanocortin (POMC) cleavage products.
Primary adrenal insufficiency lacks cortisol, resulting in high ACTH and MSH levels that stimulate melanocytes.

Key Concept

Classic physical examination findings and their associated endocrine disorders.
Question 566Question →

Match each highly specific clinical scenario to the most appropriate guideline-directed pharmacotherapy, taking into account patient-specific contraindications.

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Items

A 24-year-old pregnant woman (10 weeks gestation) presents with a 4-day history of fever, severe headache, myalgias, and a petechial rash that began on her wrists and ankles. She recently camped in a wooded area of North Carolina.
A 32-year-old pregnant woman (10 weeks gestation) presents with an expanding targetoid rash on her back and a unilateral facial nerve palsy. She has no meningeal signs or electrocardiographic abnormalities.
A 65-year-old man develops ventilator-associated pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA). He has a documented history of severe, anaphylactic allergy to vancomycin.
A 55-year-old man with acute myeloid leukemia and profound neutropenia develops persistent fever and a new pulmonary nodule with a surrounding ground-glass halo on chest computed tomography.
A 40-year-old man with advanced HIV and a severe sulfa allergy presents with fever, dry cough, and bilateral interstitial infiltrates. Arterial blood gas shows a PaO2 of 62 mmHg on room air.

Matches

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Answer

Vignette 1 matches Oral doxycycline; Vignette 2 matches Oral amoxicillin; Vignette 3 matches Intravenous linezolid; Vignette 4 matches Intravenous voriconazole; Vignette 5 matches Intravenous pentamidine plus corticosteroids.
Each clinical scenario presents a specific infectious disease paired with unique constraints requiring highly targeted therapy. RMSF in pregnancy must still be treated with doxycycline due to disease lethality. Lyme disease in pregnancy with isolated facial palsy allows for the safe alternative of amoxicillin. MRSA pneumonia in a vancomycin-allergic patient necessitates linezolid. Invasive aspergillosis in neutropenia requires voriconazole. Severe PCP with a sulfa allergy requires alternative coverage (pentamidine) alongside vital corticosteroids.

Step-by-Step Solution

1
Analyze Vignette 1: Identify Rickettsia rickettsii (RMSF) infection in a pregnant patient.
Match with Oral doxycycline.
Doxycycline is the sole exception to the tetracycline contraindication in pregnancy when treating life-threatening RMSF.
2
Analyze Vignette 2: Identify Borrelia burgdorferi (Lyme disease) with isolated facial palsy in a pregnant patient.
Match with Oral amoxicillin.
Amoxicillin is safe in pregnancy and effective for early Lyme with isolated facial palsy; doxycycline must be avoided here as safer alternatives exist.
3
Analyze Vignette 3: Identify MRSA pneumonia in a patient with a vancomycin allergy.
Match with Intravenous linezolid.
Linezolid has excellent lung penetration. Daptomycin cannot be used because it is inactivated by surfactant.
4
Analyze Vignette 4: Identify the CT halo sign in a neutropenic host as invasive pulmonary aspergillosis.
Match with Intravenous voriconazole.
Voriconazole is the first-line targeted antifungal for invasive aspergillosis.
5
Analyze Vignette 5: Identify severe Pneumocystis jirovecii pneumonia (PaO2 of 62 mmHg) in a sulfa-allergic patient.
Match with Intravenous pentamidine plus corticosteroids.
Severe PCP requires adjunctive corticosteroids to prevent inflammatory respiratory failure, and pentamidine replaces TMP-SMX in severe allergy.

Key Concept

The management of complex infectious diseases requires critical adjustment of first-line therapies based on strict patient-specific factors such as pregnancy, anaphylactic allergies, and the anatomical site of infection.
Question 567Question →

A 28-year-old woman comes to the clinic reporting profound fatigue, generalized weakness, and frequent dizzy spells over the past six months. She gave birth to her first child eight months ago. The delivery was complicated by severe uterine atony that required a massive blood transfusion and uterine artery embolization. She has not resumed menstruation and reports that she was completely unable to produce breast milk postpartum. The patient also notes recent cold intolerance and a 4-kg (8.8-lb) weight loss. Her blood pressure is 86/56 mmHg seated and 74/48 mmHg standing. Her heart rate is 92/min. Physical examination reveals delayed relaxation of deep tendon reflexes and a noticeable loss of pubic and axillary hair. Laboratory studies show:

Sodium: 133 mEq/L
Potassium: 4.2 mEq/L
Thyroid-stimulating hormone (TSH): 1.4 μ\mu U/mL (Normal: 0.4–4.0 μ\mu U/mL)
Free thyroxine (T4): 0.5 ng/dL (Normal: 0.9–1.7 ng/dL)

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

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Answer: Assess morning serum cortisol and adrenocorticotropic hormone levels

Answer

Assess morning serum cortisol and adrenocorticotropic hormone levels
The patient's clinical presentation (postpartum hemorrhage, failure to lactate, amenorrhea, hypotension) and laboratory findings (low free T4 with an inappropriately normal TSH) are classic for Sheehan syndrome (postpartum pituitary necrosis). This condition causes panhypopituitarism, meaning she likely has both central hypothyroidism and central adrenal insufficiency. A critical rule in endocrinology is that before initiating thyroid hormone replacement in any patient with suspected hypopituitarism, the adrenal axis must be evaluated (e.g., with 8 AM cortisol and ACTH). Initiating thyroid hormone increases the metabolic clearance of cortisol. If a patient has underlying, untreated adrenal insufficiency, giving levothyroxine will rapidly deplete their remaining cortisol, precipitating a life-threatening adrenal crisis.

Step-by-Step Solution

1
Analyze the patient's history and symptoms.
The history of postpartum hemorrhage, failure to lactate, amenorrhea, and loss of pubic hair points toward panhypopituitarism (Sheehan syndrome).
Ischemic necrosis of the pituitary gland during complicated childbirth affects multiple endocrine axes, including prolactin, gonadotropins, TSH, and ACTH.
2
Interpret the laboratory findings.
A low Free T4 with an inappropriately normal TSH indicates central (secondary) hypothyroidism. The normal potassium level suggests the renin-angiotensin-aldosterone system is intact, characteristic of central adrenal insufficiency.
Primary hypothyroidism would feature an elevated TSH, whereas central hypothyroidism features a low or inappropriately normal TSH. Primary adrenal insufficiency would feature hyperkalemia, which is absent here.
3
Determine the appropriate management sequence.
The adrenal axis must be evaluated with a morning cortisol and ACTH level (or cosyntropin stimulation test) before initiating thyroid hormone.
Thyroid hormone increases the hepatic clearance of cortisol. Giving levothyroxine to a patient with untreated adrenal insufficiency can precipitate a lethal acute adrenal crisis.

Key Concept

In patients with suspected panhypopituitarism (e.g., central hypothyroidism), the adrenal axis must be evaluated and treated with glucocorticoids before initiating levothyroxine therapy to prevent an acute adrenal crisis.
Question 568Question →

A 34-year-old man with advanced, untreated HIV infection is evaluated in the emergency department for a two-week history of constant, severe headaches, low-grade fevers, and intermittent nausea. He appears lethargic. Vital signs show a temperature of 38.1°C (100.6°F), blood pressure of 118/76 mmHg, and a heart rate of 92/min. Neurologic examination shows mild nuchal rigidity but no focal deficits. Laboratory studies confirm a CD4 count of 18 cells/mm³. A lumbar puncture is performed, demonstrating an elevated opening pressure of 290 mm H2O. Cerebrospinal fluid (CSF) analysis reveals 45 leukocytes/mm³ (90% lymphocytes), a glucose level of 32 mg/dL, and a protein level of 88 mg/dL. A CSF India ink stain displays encapsulated budding yeast, and the cryptococcal antigen assay is profoundly positive.

Arrange the following therapeutic interventions in the most appropriate chronological order of their initiation for the optimal management of this patient.

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Answer

The correct chronological sequence of initiation is: Induction with amphotericin B and flucytosine (Week 0), followed by consolidation with high-dose fluconazole (Week 2), followed by initiation of ART (Week 4-6), and finally maintenance with low-dose fluconazole (Week 10).
The management of HIV-associated cryptococcal meningitis follows a rigorous chronological protocol. First, an induction phase (weeks 0-2) utilizes fungicidal liposomal amphotericin B and flucytosine. Second, a consolidation phase (weeks 2-10) uses high-dose fluconazole (400 mg daily). Third, combination ART is uniquely delayed in cryptococcal meningitis to 4-6 weeks after antifungal initiation to prevent fatal CNS IRIS, placing its initiation appropriately within the consolidation phase. Finally, maintenance therapy with low-dose fluconazole (200 mg daily) begins at week 10 after consolidation is complete.

Step-by-Step Solution

1
Diagnose the underlying condition.
The patient has HIV-associated cryptococcal meningitis.
The diagnosis is confirmed by the profoundly low CD4 count, symptoms of elevated intracranial pressure, and CSF findings positive for encapsulated budding yeast (India ink) and cryptococcal antigen.
2
Identify the first phase of pharmacologic treatment (Induction).
Initiate intravenous liposomal amphotericin B and oral flucytosine.
Induction therapy requires potent fungicidal agents for 2 weeks to rapidly sterilize the cerebrospinal fluid and reduce mortality.
3
Identify the second phase of treatment (Consolidation).
Transition to oral fluconazole 400 mg daily.
After 2 weeks of successful induction, therapy is stepped down to high-dose oral fluconazole for an 8-week consolidation phase to ensure the infection does not relapse.
4
Determine the optimal timing for starting antiretroviral therapy (ART).
Initiate combination ART.
Unlike most opportunistic infections, ART in cryptococcal meningitis must be delayed for 4 to 6 weeks after starting antifungal therapy to avoid fatal central nervous system immune reconstitution inflammatory syndrome (IRIS). Therefore, ART is started during the consolidation phase.
5
Identify the final ongoing phase of treatment (Maintenance).
Transition to oral fluconazole 200 mg daily.
After completing the 8-week consolidation phase (at week 10 overall), the patient is transitioned to lower-dose maintenance therapy to provide secondary prophylaxis until the immune system recovers.

Key Concept

The management of HIV-associated cryptococcal meningitis requires a strict, multi-phase antifungal regimen (induction, consolidation, maintenance) with carefully delayed initiation of antiretroviral therapy to prevent severe immune reconstitution inflammatory syndrome (IRIS).
Estimated Time:2m 0s
Question 569Question →

An emergency medical services team arrives at the hospital with an altered, lethargic male patient who was found severely confused at home by his family. The patient is 6868 years old and has a known history of extensive tobacco use (4040 pack-years). According to his family, he has experienced worsening constipation and fatigue over the last seven days. Vital signs upon arrival include a temperature of 37.2∘C37.2^\circ\text{C} (99.0∘F99.0^\circ\text{F}), a blood pressure of 98/58 mm Hg98/58\text{ mm Hg}, and a heart rate of 112/min112/\text{min}. Clinical evaluation demonstrates pronounced signs of volume depletion, including parched oral mucosa and delayed capillary refill. Urgent serum chemistries reveal a total calcium concentration of 15.6 mg/dL15.6\text{ mg/dL}, an albumin concentration of 3.8 g/dL3.8\text{ g/dL}, and a creatinine of 2.1 mg/dL2.1\text{ mg/dL} (previously 0.9 mg/dL0.9\text{ mg/dL}). An electrocardiogram demonstrates a shortened QT interval.

Arrange the following therapeutic and diagnostic interventions in the most appropriate chronological sequence for managing this patient's acute presentation, from immediate life-saving stabilization to definitive evaluation.

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Answer

The correct sequence for managing severe symptomatic hypercalcemia is to first initiate aggressive volume expansion with isotonic saline, followed by rapid-acting calcitonin, then sustained-acting bisphosphonates, and finally concluding with a diagnostic workup for the underlying cause.
The correct chronological approach prioritizes interventions based on their onset of action and physiological necessity. Severe hypercalcemia causes marked volume depletion, making immediate aggressive hydration with isotonic normal saline the paramount first step. Once fluid resuscitation is underway, calcitonin is administered because it rapidly lowers serum calcium within 4 to 6 hours. Because calcitonin's effect is transient (tachyphylaxis occurs within 48 hours), an intravenous bisphosphonate is also administered; however, its maximum effect takes 48 to 72 hours, placing it conceptually after calcitonin in the timeline of action. Finally, after stabilizing the acute life-threatening metabolic derangement, the clinician must pursue a targeted diagnostic workup to establish the underlying etiology and direct definitive treatment.

Step-by-Step Solution

1
Recognize severe, symptomatic hypercalcemia and assess fluid status.
The patient has a serum calcium >14 mg/dL> 14\text{ mg/dL} with neurologic symptoms and profound volume depletion.
Determines the necessity for immediate, aggressive inpatient intervention rather than outpatient evaluation.
2
Address the patient's critical volume depletion.
Isotonic normal saline is administered aggressively.
Hypercalcemia induces nephrogenic diabetes insipidus, leading to severe dehydration. Volume expansion dilutes serum calcium and significantly enhances its renal excretion.
3
Provide rapid-acting pharmacotherapy to lower serum calcium.
Calcitonin is administered.
Calcitonin acts quickly (within 44 to 66 hours) to inhibit osteoclast activity, effectively bridging the therapeutic gap until long-acting agents take effect. Its efficacy wanes after 4848 hours due to tachyphylaxis.
4
Provide sustained-acting pharmacotherapy.
An intravenous bisphosphonate is administered.
Bisphosphonates are potent inhibitors of bone resorption but take 4848 to 7272 hours to reach maximum effect, providing necessary long-term control after the calcitonin effect diminishes.
5
Identify and treat the underlying cause.
A targeted workup (e.g., PTH, PTHrP, imaging) is performed.
With the patient stabilized, establishing the primary etiology (likely malignancy in this heavy smoker) allows for definitive, directed therapy.

Key Concept

The management of severe symptomatic hypercalcemia is sequenced by pharmacologic onset of action: immediate volume expansion (isotonic saline), rapid but transient calcium reduction (calcitonin), delayed but sustained reduction (bisphosphonates), and definitive treatment of the underlying cause.
Question 570Question →

During morning rounds, a 6868-year-old female is evaluated on her third day of hospitalization for community-acquired pneumonia. She initially presented with a fever, productive cough, and worsening shortness of breath. Her medical history includes chronic obstructive pulmonary disease (COPD) and osteoarthritis. On admission, she was started on intravenous levofloxacin and oral prednisone.

Today, she reports feeling much better and is tolerating a regular diet. Her temperature is 37.1∘C37.1^\circ C (98.8∘F98.8^\circ F), blood pressure is 128/78128/78 mm Hg, pulse is 8282/min, and respiratory rate is 1616/min. Pulse oximetry shows 94%94\% on room air.

Physical examination reveals a normal jugular venous pressure of 66 cm H2OH_2O. Lung auscultation shows prolonged expiration and scattered end-expiratory wheezes, but the bibasilar crackles heard on admission have resolved. She has trace bilateral pitting edema at the ankles, which is unchanged from her baseline.

Laboratory results from this morning show:
Leukocyte count: 7,500/mm37,500/mm^3
Thyroid-stimulating hormone (TSH): 0.60.6 μU/mL\mu U/mL (Normal: 0.4−4.00.4-4.0 μU/mL\mu U/mL)
Free thyroxine (T4): 0.70.7 ng/dL (Normal: 0.9−1.70.9-1.7 ng/dL)

Arterial blood gas (room air):
pHpH: 7.387.38
PaCO2PaCO_2: 5454 mm Hg
PaO2PaO_2: 7272 mm Hg
HCO3−HCO_3^-: 3131 mEq/L

Sputum cultures obtained on admission have grown Streptococcus pneumoniae that is susceptible to penicillin, amoxicillin, ceftriaxone, levofloxacin, and vancomycin.

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

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Answer: Transition to oral amoxicillin

Answer

Transition to oral amoxicillin
This patient was admitted for a community-acquired pneumonia (CAP) exacerbation of her COPD and was appropriately started on empiric intravenous levofloxacin. She is now clinically stable, afebrile, and tolerating an oral diet, meeting the criteria for transition to oral antibiotics. Her sputum culture grew Streptococcus pneumoniae that is susceptible to narrow-spectrum agents such as penicillin and amoxicillin. Good antibiotic stewardship dictates stepping down from a broad-spectrum intravenous fluoroquinolone to a targeted, narrow-spectrum oral agent (like amoxicillin) to minimize collateral damage, such as Clostridioides difficile infection, and to prevent the development of antimicrobial resistance.

Step-by-Step Solution

1
Assess the patient's clinical trajectory and readiness for step-down therapy.
The patient is afebrile, hemodynamically stable, breathing comfortably on room air, and tolerating an oral diet.
These criteria indicate that the patient no longer requires intravenous antibiotics or acute hospital-level interventions.
2
Review the microbiological data to tailor therapy.
Sputum culture grew Streptococcus pneumoniae that is fully susceptible to multiple agents, including penicillin and amoxicillin.
Empiric broad-spectrum therapy should be narrowed once culture and sensitivity data are available.
3
Select the most appropriate targeted therapy.
Oral amoxicillin is selected over continuing intravenous levofloxacin.
Amoxicillin is a highly effective, narrow-spectrum oral agent for susceptible S. pneumoniae, aligning with principles of antibiotic stewardship to reduce collateral damage and resistance.

Key Concept

Antibiotic Stewardship and De-escalation
Question 571Question →

A 32-year-old woman is brought to the emergency department by her husband due to progressive lethargy, profound fatigue, and confusion over the past 24 hours. She gave birth to her second child 6 weeks ago; the delivery was complicated by uterine atony and severe postpartum hemorrhage requiring massive blood transfusions. Since discharge, she has been unable to breastfeed and has not resumed menstruation. Her husband mentions she has been very withdrawn and tearful, and he is concerned she might have bipolar disorder like her mother. On physical examination, the patient is somnolent. Temperature is 36.1°C (97.0°F), blood pressure is 82/50 mmHg, and pulse is 112/min. Capillary refill is 4 seconds. Laboratory studies show:

Sodium: 129 mEq/L
Potassium: 4.2 mEq/L
Thyroid-stimulating hormone (TSH): 1.2 µU/mL (Normal: 0.4–4.0 µU/mL)
Free thyroxine (T4): 0.4 ng/dL (Normal: 0.9–1.7 ng/dL)

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

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Answer: Administer intravenous hydrocortisone

Answer

Administer intravenous hydrocortisone
This patient's presentation of hemodynamic instability, profound fatigue, hyponatremia, and central hypothyroidism (low Free T4 with an inappropriately normal TSH) following a complicated delivery with severe hemorrhage is highly characteristic of Sheehan syndrome (postpartum pituitary necrosis). The loss of anterior pituitary function leads to panhypopituitarism, including secondary adrenal insufficiency due to a lack of ACTH. In the setting of an acute adrenal crisis (evidenced by hypotension, altered mental status, and hyponatremia), the most critical and immediate step is the administration of intravenous hydrocortisone (stress-dose corticosteroids) to restore vascular tone and prevent cardiovascular collapse.

Step-by-Step Solution

1
Identify the underlying diagnosis based on the patient's obstetric history and current symptoms.
The history of severe postpartum hemorrhage, failure to lactate, amenorrhea, and central hypothyroidism points to Sheehan syndrome (ischemic necrosis of the pituitary gland).
Hypotensive shock during delivery causes ischemia to the enlarged pituitary gland, leading to panhypopituitarism.
2
Recognize the acute life-threatening complication.
The patient has severe hypotension, tachycardia, altered mental status, and hyponatremia, indicating an acute adrenal crisis.
Loss of ACTH production leads to decreased cortisol, which is required to maintain vascular tone and manage physiologic stress.
3
Determine the most appropriate immediate step in management.
Immediate administration of intravenous hydrocortisone (stress-dose corticosteroids) is required.
Glucocorticoid replacement is life-saving in adrenal crisis and must be given before any other hormone replacement (such as levothyroxine) to prevent worsening of the crisis.

Key Concept

In patients with panhypopituitarism presenting with an acute adrenal crisis, immediate administration of intravenous glucocorticoids is the critical first step and must precede thyroid hormone replacement.
Estimated Time:1m 30s
Question 572Question →

A 71-year-old man with a history of a cerebrovascular accident and neurogenic bladder managed with a chronic indwelling urethral catheter is evaluated during a routine home health visit. He reports feeling well and denies fever, chills, flank pain, suprapubic discomfort, or increased spasticity. His temperature is 37.0∘C37.0^\circ\text{C} (98.6∘F98.6^\circ\text{F}), blood pressure is 130/80 mmHg130/80\text{ mmHg}, heart rate is 76/min76/\text{min}, and respiratory rate is 14/min14/\text{min}. Physical examination reveals a soft, non-tender abdomen and no costovertebral angle tenderness. The urine in his collection bag appears cloudy. A urinalysis reveals positive leukocyte esterase and 3030 white blood cells per high-power field. A urine culture obtained 48 hours ago grows >100,000 CFU/mL>100,000\text{ CFU/mL} of *Pseudomonas aeruginosa*. Which of the following is the most appropriate next step in management?

Show answer & explanation

Answer: Observation without antimicrobial therapy

Answer

Observation without antimicrobial therapy.
The correct approach is observation without antimicrobial therapy. This patient presents with classic asymptomatic bacteriuria in the setting of a chronic indwelling urinary catheter. Virtually all patients with chronic indwelling catheters will develop bacteriuria (positive urine culture) and pyuria (white blood cells in the urine) within a few weeks due to biofilm formation. Because the patient is entirely asymptomatic, hemodynamically stable, and lacks signs of invasive infection, treating the culture result constitutes poor antibiotic stewardship. Eradicating the colonizing bacteria does not improve clinical outcomes and only serves to increase the risk of adverse drug events and the emergence of multidrug-resistant organisms.

Step-by-Step Solution

1
Assess the patient for signs and symptoms of systemic or localized infection.
The patient is afebrile, hemodynamically stable, and has no localizing symptoms such as suprapubic pain or costovertebral angle tenderness.
Differentiating between a true urinary tract infection and asymptomatic colonization is the critical first step in management.
2
Interpret the urinalysis and urine culture findings in the context of an indwelling catheter.
The presence of pyuria and >100,000 CFU/mL of Pseudomonas aeruginosa indicates bacteriuria, which is a universal and expected finding in chronically catheterized patients.
Chronic foreign bodies in the urinary tract inevitably become colonized with bacteria, leading to chronic pyuria and positive cultures.
3
Determine the appropriate intervention based on established antibiotic stewardship guidelines.
No antibiotics are prescribed.
Treatment of asymptomatic bacteriuria is contraindicated except in specific populations (e.g., pregnant women, patients undergoing urologic procedures), as it promotes antimicrobial resistance.

Key Concept

Management of asymptomatic bacteriuria and catheter colonization.
Estimated Time:1m 0s
Question 573Question →

A 11-hour-old male neonate is evaluated in the neonatal intensive care unit for respiratory distress. He was delivered at 3737 weeks gestation via an elective, scheduled cesarean delivery to a 2828-year-old gravida 2, para 2 mother. The mother's pregnancy was uncomplicated, and there is no history of prolonged rupture of membranes, maternal fever, or meconium-stained amniotic fluid. Birth weight is 3100 g3100\text{ g}. Apgar scores were 77 and 88 at 11 and 55 minutes, respectively. Vital signs are temperature 37.0∘C37.0^\circ\text{C} (98.6∘F98.6^\circ\text{F}), heart rate 155/min155/\text{min}, and respiratory rate 72/min72/\text{min}. Physical examination reveals an infant with mild intercostal retractions, nasal flaring, and grunting. Breath sounds are clear and equal bilaterally with no murmurs.

An arterial blood gas on room air reveals the following:

MeasurementValueReference Range
pHpH7.327.327.35−7.457.35 - 7.45
pCO2pCO_250 mm Hg50\text{ mm Hg}35−45 mm Hg35 - 45\text{ mm Hg}
pO2pO_260 mm Hg60\text{ mm Hg}50−80 mm Hg50 - 80\text{ mm Hg}
HCO3−HCO_3^-24 mEq/L24\text{ mEq/L}22−28 mEq/L22 - 28\text{ mEq/L}

A chest radiograph demonstrates lung hyperinflation, prominent perihilar vascular markings, and fluid within the interlobar fissures. Which of the following is the most appropriate next step in the management of this patient?

Show answer & explanation

Answer: Provide supportive care with oxygen supplementation or continuous positive airway pressure

Answer

Provide supportive care with oxygen supplementation or continuous positive airway pressure
The neonate presents with classic signs of transient tachypnea of the newborn (TTN), characterized by early-onset respiratory distress in a term or late-preterm infant, especially following a cesarean delivery without labor. The pathophysiology involves delayed resorption and clearance of fetal alveolar fluid. The chest radiograph findings of hyperinflation, prominent perihilar streaking, and fluid in the interlobar fissures are pathognomonic. TTN is a self-limiting condition, and the most appropriate next step is supportive care, which includes providing supplemental oxygen or continuous positive airway pressure (CPAP) to maintain adequate oxygenation while the fluid is naturally resorbed over 24 to 72 hours.

Step-by-Step Solution

1
Analyze the patient's gestational age, delivery method, and risk factors.
The patient is a 37-week (term) neonate born via scheduled cesarean delivery without labor, with no infectious risk factors.
Scheduled cesarean sections bypass the physiological stress of labor, leading to decreased catecholamine release, which normally triggers the resorption of fetal lung fluid.
2
Interpret the physical examination and laboratory findings.
The infant exhibits tachypnea and increased work of breathing within the first hour of life, accompanied by mild respiratory acidosis on the arterial blood gas.
These signs indicate acute respiratory distress, necessitating rapid identification of the underlying etiology to guide appropriate management.
3
Correlate the clinical presentation with the radiographic findings to establish a diagnosis.
The chest radiograph shows hyperinflation, perihilar vascular prominence, and fluid in the interlobar fissures, strongly indicating Transient Tachypnea of the Newborn (TTN).
These radiographic hallmarks distinguish TTN from other causes like Respiratory Distress Syndrome (which shows low lung volumes and a ground-glass appearance) or Meconium Aspiration Syndrome (patchy infiltrates).
4
Determine the most appropriate evidence-based management for the diagnosed condition.
Supportive care with supplemental oxygen or continuous positive airway pressure (CPAP) is indicated.
TTN is a benign, self-limiting condition that resolves as the lymphatic system slowly clears the retained fetal lung fluid over 1 to 3 days.

Key Concept

Transient tachypnea of the newborn (TTN) typically presents in term or late-preterm infants delivered via cesarean section without labor. It manifests as early respiratory distress with radiographic findings of retained lung fluid and is managed with supportive care.
Question 574Question →

A clinical guideline committee is creating a quick-reference protocol for managing specific infectious disease exposures. Match each patient scenario with the single most appropriate pharmacological management plan.

Click a left item, then click its matching right item

Items

A 28-year-old healthcare worker who sustained a deep needlestick injury after drawing blood from an untreated patient with a high HIV viral load.
A 32-year-old pregnant woman in active labor whose rectovaginal screening swab at 36 weeks gestation was positive for Streptococcus agalactiae.
A 19-year-old college student who shared drinks with a roommate recently hospitalized for confirmed Neisseria meningitidis meningitis.
A 45-year-old postal worker presenting with a deep puncture wound on the right hand after being bitten by a stray cat.

Matches

Show answer & explanation

Answer

Match the HIV exposure to triple ART, the GBS colonization to IV Penicillin G, the meningococcal contact to single-dose ciprofloxacin, and the cat bite to amoxicillin-clavulanate.
Each clinical scenario presents a classic, high-yield infectious exposure with a highly standardized prophylactic or empiric regimen dictated by current infectious disease guidelines. Recognizing these direct associations is fundamental to providing safe and effective urgent care.

Step-by-Step Solution

1
Evaluate the needlestick injury from an HIV-positive patient.
Identify this as a high-risk occupational exposure requiring comprehensive post-exposure prophylaxis (PEP).
Standard PEP protocols mandate a 3-drug antiretroviral regimen for 28 days.
2
Evaluate the pregnant patient in labor with a positive GBS (Streptococcus agalactiae) swab.
Identify the need for intrapartum antibiotic prophylaxis.
IV penicillin G is the first-line agent to prevent vertical transmission of GBS and subsequent neonatal sepsis.
3
Evaluate the college student exposed to Neisseria meningitidis.
Identify the need for meningococcal chemoprophylaxis.
Close contacts require eradication of nasopharyngeal carriage. A single oral dose of ciprofloxacin is highly effective and convenient.
4
Evaluate the patient with a cat bite.
Identify the risk for Pasteurella multocida and mixed oral flora.
Amoxicillin-clavulanate is the first-line empiric oral therapy for cat and dog bites due to its excellent coverage of these specific pathogens.

Key Concept

Post-exposure prophylaxis and targeted empiric therapy for common infectious exposures
Question 575Question →

A 4242-year-old woman is admitted to the hospital for profound, progressive generalized muscle weakness and a 66-kg (13.213.2-lb) weight loss over the past 33 months. She has recently noticed the new onset of dark, coarse hair on her chin and upper lip. She has a 3030-pack-year smoking history. Vital signs show a blood pressure of 174/102174/102 mm Hg. Physical examination reveals noticeable temporal wasting, generalized muscle atrophy, and hyperpigmentation along the palmar creases and oral mucosa.

Initial laboratory studies show:
Sodium (Na+Na^+): 146146 mEq/L
Potassium (K+K^+): 2.42.4 mEq/L
Chloride (Cl−Cl^-): 9696 mEq/L
Bicarbonate (HCO3−HCO_3^-): 3636 mEq/L
Glucose: 255255 mg/dL
Free T4T_4: 0.60.6 ng/dL (Normal: 0.90.9-1.71.7 ng/dL)
TSHTSH: 0.80.8 μ\mu U/mL (Normal: 0.50.5-5.05.0 μ\mu U/mL)

Which of the following is the most likely additional finding in this patient?

Show answer & explanation

Answer: Decreased serum aldosterone and decreased plasma renin activity

Answer

Decreased serum aldosterone and decreased plasma renin activity
The correct finding is decreased serum aldosterone and decreased plasma renin activity. The patient's clinical picture of rapid weight loss, hyperpigmentation, severe hypokalemic metabolic alkalosis, and a heavy smoking history is classic for ectopic ACTH production (e.g., from a lung malignancy). Ectopic ACTH causes massive, autonomous adrenal cortisol secretion. In the kidney, the enzyme 11-beta-hydroxysteroid dehydrogenase type 2 (11b-HSD2) normally protects mineralocorticoid receptors by converting active cortisol to inactive cortisone. In severe Cushing syndrome, the sheer volume of cortisol overwhelms 11b-HSD2, allowing cortisol to bind and activate mineralocorticoid receptors directly. This 'apparent mineralocorticoid excess' leads to profound sodium retention, potassium wasting, and volume expansion. The resultant hypervolemia and hypertension physiologically suppress the normal renin-angiotensin-aldosterone system, leading to low plasma renin activity and low serum aldosterone levels.

Step-by-Step Solution

1
Analyze the clinical presentation in the context of the patient's demographics and risk factors.
The combination of rapid weight loss, progressive weakness, hyperpigmentation, hirsutism, and a heavy smoking history in a middle-aged patient is highly suspicious for paraneoplastic ectopic ACTH secretion (e.g., from small cell lung cancer or a bronchial carcinoid tumor).
Recognizing the syndromic presentation of ectopic ACTH is the first step in diagnosing the underlying metabolic derangements.
2
Evaluate the metabolic and endocrine laboratory abnormalities.
The labs reveal severe hypokalemic metabolic alkalosis, hyperglycemia, and secondary hypothyroidism (low free T4, inappropriately normal TSH).
Hypercortisolism causes insulin resistance (hyperglycemia) and suppresses the hypothalamic-pituitary-thyroid axis (central hypothyroidism). The severe hypokalemia and alkalosis indicate a profound mineralocorticoid effect.
3
Determine the mechanism of the mineralocorticoid effect in ectopic ACTH syndrome.
Extremely high levels of circulating cortisol overwhelm the capacity of the renal enzyme 11-beta-hydroxysteroid dehydrogenase type 2 (11b-HSD2), which normally converts cortisol to inactive cortisone.
When 11b-HSD2 is saturated, excess cortisol binds directly to and activates mineralocorticoid receptors in the renal collecting ducts.
4
Deduce the downstream physiological effects on the renin-angiotensin-aldosterone system.
Cortisol-mediated activation of the mineralocorticoid receptors leads to intense sodium reabsorption, potassium wasting, and hydrogen ion excretion. The resulting volume expansion and hypertension suppress endogenous renin release, which in turn leads to decreased aldosterone production.
This creates a paradoxical state of apparent mineralocorticoid excess where clinical signs of hyperaldosteronism are present, but both renin and aldosterone levels are actually suppressed.

Key Concept

In ectopic ACTH syndrome, massive hypercortisolism overwhelms renal 11-beta-hydroxysteroid dehydrogenase type 2, allowing cortisol to activate mineralocorticoid receptors. This causes sodium retention and volume expansion, which physiologically suppresses both renin and aldosterone.
Question 576Question →

A 5252-year-old man is evaluated in the clinic for persistently elevated blood pressure. He is currently taking maximally tolerated doses of lisinopril, amlodipine, and hydrochlorothiazide. His blood pressure today is 168/94 mmHg168/94\text{ mmHg}, and his heart rate is 76/min76\text{/min}. Laboratory studies reveal a serum potassium level of 3.0 mEq/L3.0\text{ mEq/L} and a serum sodium level of 144 mEq/L144\text{ mEq/L}. The patient's antihypertensive regimen is transitioned to non-interfering medications (e.g., verapamil and doxazosin), and his hypokalemia is corrected with oral potassium supplementation. The physician strongly suspects a specific endocrine etiology for his resistant hypertension and hypokalemia. Arrange the following diagnostic steps in the most appropriate chronological sequence to definitively evaluate and manage this patient's suspected condition.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence is to first screen with a plasma aldosterone-to-renin ratio, second confirm the diagnosis with an intravenous saline infusion test, third localize the pathology with an adrenal computed tomography scan, and finally lateralize the hypersecretion using bilateral adrenal venous sampling.
The evaluation of primary aldosteronism (Conn syndrome) strictly follows a three-phase diagnostic algorithm: screening, confirmation, and subtype classification. Initial screening is accomplished by calculating the ratio of plasma aldosterone concentration to plasma renin activity. If this ratio is elevated, the patient undergoes dynamic confirmatory testing, typically via an intravenous saline infusion test or an oral sodium load, to prove that aldosterone secretion is autonomous and non-suppressible. Once biochemically confirmed, subtype classification begins with an adrenal computed tomography (CT) scan to assess the anatomy. However, because non-functioning adrenal incidentalomas are very common in patients over 35 years of age, imaging alone is insufficient to prove that a visualized nodule is the source of hormone excess. Therefore, the final step before surgical adrenalectomy is bilateral adrenal venous sampling to functionally confirm the lateralization of aldosterone hypersecretion.

Step-by-Step Solution

1
Screen with plasma aldosterone concentration and plasma renin activity.
Identifies individuals at high risk for primary aldosteronism.
It is the most sensitive test to detect hyperaldosteronism in patients presenting with resistant hypertension and hypokalemia.
2
Confirm diagnosis with an intravenous saline infusion test.
Demonstrates inappropriate, autonomous aldosterone secretion that fails to suppress under a sodium load.
Biochemical confirmation is mandatory before pursuing invasive or expensive anatomical imaging, as false positives can occur with the screening ratio.
3
Assess anatomy with a high-resolution adrenal computed tomography scan.
Identifies macroscopic adrenal abnormalities such as unilateral nodules, bilateral hyperplasia, or large carcinomas.
Provides an anatomical map necessary to rule out malignancy and guide subsequent invasive lateralization procedures.
4
Perform bilateral adrenal venous sampling.
Compares aldosterone levels from both adrenal veins.
Because non-functioning adrenal incidentalomas are highly prevalent in patients older than 35, this step distinguishes an active aldosterone-producing adenoma from bilateral adrenal hyperplasia, which dictates whether the patient requires surgery or medical therapy.

Key Concept

Diagnostic algorithm for primary aldosteronism
Question 577Question →

A 71-year-old man is evaluated in the clinic for a 3-month history of worsening lower back pain and generalized fatigue. The pain is deep, achy, and localized to the mid-lumbar region without radiation to the legs. He also reports new-onset constipation and increased frequency of urination. He has no significant past medical history and takes no medications. His temperature is 37.0∘C37.0^\circ\text{C} (98.6∘F98.6^\circ\text{F}), blood pressure is 142/88142/88 mmHg, pulse is 8484/min, and respiratory rate is 1414/min. Physical examination shows midline point tenderness over the L4 vertebra. Neurologic examination of the lower extremities shows 5/55/5 strength with normal deep tendon reflexes.

Laboratory results are as follows:

Laboratory TestResult
Hemoglobin9.19.1 g/dL
Leukocytes6,800/mm36,800/\text{mm}^3
Platelets210,000/mm3210,000/\text{mm}^3
Blood urea nitrogen3838 mg/dL
Serum creatinine2.22.2 mg/dL
Serum calcium11.911.9 mg/dL
Total serum protein9.29.2 g/dL
Serum albumin3.53.5 g/dL

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

Show answer & explanation

Answer: Serum and urine protein electrophoresis

Answer

Serum and urine protein electrophoresis
This patient's clinical presentation is highly suspicious for multiple myeloma, characterized by the CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lytic lesions). A critical diagnostic clue is the significant protein gap (total serum protein minus serum albumin >4> 4 g/dL), which strongly suggests the presence of a circulating monoclonal immunoglobulin (M-protein). The most appropriate initial step to evaluate for a monoclonal gammopathy is serum and urine protein electrophoresis (SPEP and UPEP), often combined with immunofixation. If a monoclonal spike is detected, a bone marrow biopsy is subsequently performed to confirm the diagnosis.

Step-by-Step Solution

1
Analyze the clinical presentation and physical examination.
An elderly man presents with progressive lower back pain, bony tenderness, fatigue, polyuria, and constipation.
To identify key symptoms that suggest a systemic oncologic or endocrine condition rather than isolated mechanical back pain.
2
Evaluate the laboratory panel for specific diagnostic clues.
The patient has anemia, acute kidney injury (elevated BUN/creatinine), severe hypercalcemia, and a massive protein gap (Total protein 9.29.2 - Albumin 3.53.5 = 5.75.7 g/dL).
To synthesize the findings into a unifying diagnosis, recognizing the classic CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lesions) of multiple myeloma.
3
Determine the most appropriate initial diagnostic test.
The constellation of findings is highly suspicious for multiple myeloma. The initial test of choice to identify the underlying monoclonal gammopathy is serum and urine protein electrophoresis.
To confirm the presence of an M-spike (monoclonal protein) before proceeding to definitive bone marrow biopsy.

Key Concept

The classic presentation of multiple myeloma includes the CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lytic lesions) alongside a significant protein gap (>4 g/dL). Initial diagnosis requires identification of a monoclonal protein using serum and urine protein electrophoresis.
Estimated Time:1m 15s
Question 578Question →

Review the following clinical presentations and arterial blood gas results. Which primary acid-base disorder best matches each clinical vignette?

Click a left item, then click its matching right item

Items

A 22-year-old woman with type 1 diabetes presents with rapid breathing. Arterial blood gas shows pH 7.28, pCO2 28 mmHg, and HCO3 12 mEq/L.
A 68-year-old man with severe COPD presents with worsened dyspnea. Arterial blood gas shows pH 7.26, pCO2 65 mmHg, and HCO3 28 mEq/L.
A 19-year-old woman presents with carpopedal spasm during a panic attack. Arterial blood gas shows pH 7.52, pCO2 22 mmHg, and HCO3 20 mEq/L.
A 55-year-old man with peptic ulcer disease presents with 3 days of intractable vomiting. Arterial blood gas shows pH 7.54, pCO2 48 mmHg, and HCO3 40 mEq/L.
A 45-year-old woman presents with 4 days of severe watery diarrhea. Arterial blood gas shows pH 7.31, pCO2 32 mmHg, and HCO3 16 mEq/L. Serum sodium is 140 mEq/L, and chloride is 114 mEq/L.

Matches

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Answer

The correct matches pair each clinical scenario with its hallmark primary acid-base disturbance: DKA with High anion gap metabolic acidosis; COPD exacerbation with Acute respiratory acidosis; panic attack with Acute respiratory alkalosis; vomiting with Metabolic alkalosis; and diarrhea with Normal anion gap metabolic acidosis.
Each vignette represents a classic primary acid-base disorder. Diabetic ketoacidosis causes a high anion gap metabolic acidosis. Acute COPD exacerbation causes CO2 retention and acute respiratory acidosis. Panic attacks cause hyperventilation and acute respiratory alkalosis. Intractable vomiting causes loss of gastric acid, resulting in metabolic alkalosis. Severe diarrhea causes direct loss of bicarbonate, resulting in a normal anion gap metabolic acidosis.

Step-by-Step Solution

1
Analyze the pH to determine acidemia (pH < 7.35) or alkalemia (pH > 7.45).
Vignettes 1, 2, and 5 have acidemia. Vignettes 3 and 4 have alkalemia.
Establishing the primary direction of the pH change is the first step in acid-base interpretation.
2
Evaluate the pCO2 and HCO3 to identify the primary disorder causing the pH shift.
Vignettes 1 and 5 have primary decreases in HCO3 (metabolic acidosis). Vignette 2 has a primary increase in pCO2 (respiratory acidosis). Vignette 3 has a primary decrease in pCO2 (respiratory alkalosis). Vignette 4 has a primary increase in HCO3 (metabolic alkalosis).
The parameter that shifts in the same direction as the pH defines the primary disorder.
3
Calculate the serum anion gap for the cases of metabolic acidosis.
In vignette 5 (diarrhea), the anion gap is normal: 140 - (114 + 16) = 10 mEq/L. Vignette 1 (DKA) is a classic cause of high anion gap metabolic acidosis.
Differentiating normal from high anion gap metabolic acidosis is essential for identifying the correct etiology.

Key Concept

Interpretation of primary acid-base disorders based on arterial blood gas and clinical context.
Question 579Question →

A 48-year-old man presents to the clinic reporting progressive enlargement of his hands and feet over the past 44 years. He recently had to resize his wedding ring and notes that his shoes no longer fit. He also complains of increased sweating, joint pain, and frequent frontal headaches. His wife mentions that his jaw has become more prominent and there are new gaps between his teeth. His blood pressure is 165/95165/95 mmHg. Arrange the following steps in the most appropriate chronological order for the diagnostic workup and initial definitive management of this patient's suspected condition.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence for the evaluation and management of suspected acromegaly is: (1) Measure serum IGF-1, (2) Perform an OGTT with GH measurement, (3) Obtain a pituitary MRI, (4) Perform visual field testing, and (5) Proceed with transsphenoidal surgery.
The diagnostic algorithm for acromegaly requires proving biochemical excess before anatomical localization. Due to the pulsatile nature of growth hormone (GH), random GH levels are clinically useless. Therefore, the most appropriate initial screening test is measuring insulin-like growth factor 1 (IGF-1), which reflects average GH levels over days. If IGF-1 is elevated, autonomous GH secretion must be confirmed dynamically. The gold standard confirmatory test is the oral glucose tolerance test (OGTT); normally, a glucose load suppresses GH, but in acromegaly, GH remains unsuppressed. Only after biochemical confirmation should anatomical localization with a pituitary MRI be pursued. Because GH-secreting tumors are often macroadenomas (>10 mm) that can compress the optic chiasm, formal visual field perimetry is a necessary preoperative step to document deficits such as bitemporal hemianopsia. Finally, the first-line definitive treatment is surgical resection via a transsphenoidal approach.

Step-by-Step Solution

1
Measure serum IGF-1 concentration.
Serves as the initial screening test.
Growth hormone (GH) secretion is highly pulsatile, making random GH levels unreliable. IGF-1 provides a stable reflection of integrated GH secretion over time.
2
Perform OGTT with GH measurement.
Serves as the confirmatory biochemical test.
Normal physiology dictates that a glucose load suppresses GH. Failure to suppress GH definitively confirms the autonomous hypersecretion seen in acromegaly.
3
Obtain pituitary MRI.
Localizes the pituitary tumor.
Once the disease is biochemically confirmed, imaging is required to visualize the adenoma (which is usually a macroadenoma) before any physical intervention.
4
Perform formal visual field perimetry.
Assesses for optic chiasm compression.
Given the patient's headaches and the high likelihood of a macroadenoma, assessing for bitemporal hemianopsia is a critical preoperative step for surgical planning.
5
Proceed with transsphenoidal adenomectomy.
Provides definitive management.
Surgical resection is the first-line definitive treatment for GH-secreting pituitary adenomas, alleviating both hormone excess and mass effect.

Key Concept

The diagnostic algorithm for acromegaly dictates biochemical confirmation of autonomous hormone excess prior to anatomical imaging to avoid diagnostic confusion from incidentalomas.
Estimated Time:1m 30s
Question 580Question →

During a routine follow-up, a 28-year-old female patient complains of new-onset fatigue and profound muscle weakness. She has a notable past medical history of recurrent nephrolithiasis. Her vital signs are within normal limits.

Laboratory testing reveals the following values:

Serum ParameterValue
Sodium (Na+Na^+)138 mEq/L
Potassium (K+K^+)2.8 mEq/L
Chloride (Cl−Cl^-)112 mEq/L
Bicarbonate (HCO3−HCO_3^-)14 mEq/L
Urine ParameterValue
Sodium (Na+Na^+)65 mEq/L
Potassium (K+K^+)25 mEq/L
Chloride (Cl−Cl^-)55 mEq/L
pH6.8

To help differentiate the cause of her normal anion gap metabolic acidosis, the attending physician requests calculation of the urine anion gap.

What is this patient's urine anion gap (in mEq/L)?

Show answer & explanation

Answer: 35

Answer

35
The patient presents with a normal anion gap metabolic acidosis (NAGMA), likely secondary to type 1 (distal) renal tubular acidosis given her severe hypokalemia, nephrolithiasis, and alkaline urine pH. To confirm the renal etiology, the urine anion gap is calculated using the formula UNa+UK−UClU_{Na} + U_{K} - U_{Cl}. Plugging in the patient's urine electrolyte values yields 65+25−55=3565 + 25 - 55 = 35 mEq/L. A positive urine anion gap indicates impaired renal ammonium excretion, which points toward a renal tubular acidosis rather than gastrointestinal bicarbonate loss (where the UAG would typically be negative).

Step-by-Step Solution

1
Identify the standard formula used for calculating the urine anion gap.
UAG=UNa+UK−UClUAG = U_{Na} + U_{K} - U_{Cl}
The urine anion gap is used to indirectly estimate urinary ammonium excretion when evaluating a normal anion gap metabolic acidosis.
2
Select the correct values from the laboratory data table.
Urine Na+=65Na^+ = 65 mEq/L, Urine K+=25K^+ = 25 mEq/L, Urine Cl−=55Cl^- = 55 mEq/L.
It is crucial to use urine electrolytes, not serum electrolytes, for this specific calculation.
3
Calculate the final result by plugging the values into the formula.
65+25−55=3565 + 25 - 55 = 35
Performing the arithmetic determines whether the gap is positive or negative, which aids in narrowing the differential diagnosis.

Key Concept

The urine anion gap (UAG) is calculated as UNa+UK−UClU_{Na} + U_{K} - U_{Cl} and provides an indirect measurement of urinary ammonium excretion to help distinguish between renal and gastrointestinal causes of a normal anion gap metabolic acidosis.
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