Internal Medicine Practice Questions — USMLE Step 2 CK — Page 39

Match the following synovial fluid analysis findings to their most likely corresponding joint disorder.

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Answer

Needle-shaped negative crystals correspond to gouty arthritis. Rhomboid-shaped positive crystals correspond to calcium pyrophosphate deposition disease. Opaque fluid with >50,000 leukocytes corresponds to septic arthritis. Clear fluid with <2,000 leukocytes corresponds to osteoarthritis.

The correct matches rely on standard synovial fluid diagnostic criteria. Noninflammatory fluid (leukocytes

<2,000/\mu\text{L}

) points to osteoarthritis. Purulent fluid with highly elevated leukocytes (

>50,000/\mu\text{L}

) and neutrophil dominance indicates septic arthritis and requires immediate intervention. Crystal arthropathies are differentiated by their unique microscopic profiles: gout presents with negatively birefringent needle-like urate crystals, whereas pseudogout presents with positively birefringent rhomboid calcium pyrophosphate crystals.

Step-by-Step Solution

1

Evaluate the synovial fluid leukocyte count and differential.

Identify whether the fluid is noninflammatory (

<2,000/\mu\text{L}

), inflammatory, or purulent/septic (

>50,000/\mu\text{L}

).

This broad categorization separates degenerative processes (osteoarthritis) from highly dangerous acute infections (septic arthritis).

2

Analyze the polarized light microscopy findings for crystals.

Differentiate between monosodium urate and calcium pyrophosphate crystals based on shape and birefringence.

Crystal shape and optical properties definitively distinguish between the two primary crystal arthropathies: gout and pseudogout.

Key Concept

Synovial Fluid Analysis in Rheumatology

Estimated Time:45s

Question 762Question →

A 67-year-old man presents to the emergency department with a 2-day history of severe, progressively worsening shortness of breath. He reports coughing up frothy, clear sputum and states he had to sleep sitting in a recliner last night due to a feeling of suffocation when lying flat. His medical history includes long-standing hypertension, type 2 diabetes mellitus, and a 45-pack-year smoking history. He takes amlodipine and metformin.

Temperature is 37.0°C (98.6°F), blood pressure is 185/105 mmHg, pulse is 112/min, and respirations are 28/min. Pulse oximetry is 86% on room air. The patient is using accessory muscles of respiration. Jugular venous distension is present up to the angle of the mandible while the patient is sitting at a 45-degree angle. Lung auscultation reveals diffuse, bilateral end-expiratory wheezes and scattered crackles at the lung bases. Cardiac examination shows a regular rhythm, tachycardia, and a distinct S4 gallop. Bilateral 2+ pitting edema is noted in the lower extremities.

Laboratory studies show:
Leukocyte count: 9,200/mm³
Procalcitonin: $0.03$ ng/mL (normal: $< 0.15$ ng/mL)
Arterial blood gas (room air): pH $7.28$ , PaCO $_2$ $55$ mmHg, PaO $_2$ $52$ mmHg, HCO $_3^-$ $25$ mEq/L

Chest radiograph shows cardiomegaly, peribronchial cuffing, enlarged pulmonary veins, and prominent interlobular septal lines without focal opacities.

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

Intravenous furosemide, sublingual nitroglycerin, and noninvasive positive pressure ventilation

Inhaled albuterol-ipratropium, systemic methylprednisolone, and oral doxycycline

Intravenous ceftriaxone, oral azithromycin, and inhaled albuterol

Intravenous sodium bicarbonate, inhaled albuterol, and endotracheal intubation

Intravenous piperacillin-tazobactam, aggressive intravenous crystalloid resuscitation, and supplemental oxygen

Show answer & explanation

Answer: Intravenous furosemide, sublingual nitroglycerin, and noninvasive positive pressure ventilation

Answer

The most appropriate management is administering intravenous furosemide, sublingual nitroglycerin, and noninvasive positive pressure ventilation.

The correct sequence of therapies addresses all components of this patient's acute decompensated heart failure (ADHF). The patient's presentation of orthopnea, marked jugular venous distension, an S4 gallop, and radiographic evidence of pulmonary edema confirms ADHF. The wheezing is known as 'cardiac asthma,' occurring when perivascular and peribronchial edema narrows the small airways. The patient is also severely hypertensive and in acute respiratory failure (acute respiratory acidosis on ABG). Management requires a three-pronged approach: 1) Intravenous furosemide to reduce volume overload via diuresis; 2) Sublingual or intravenous nitroglycerin to rapidly reduce preload and afterload, helping the failing left ventricle pump against the severe hypertension (185/105 mmHg); and 3) Noninvasive positive pressure ventilation (NIPPV), such as CPAP or BiPAP, which improves oxygenation, decreases the work of breathing, and further reduces left ventricular preload and afterload by increasing intrathoracic pressure.

Step-by-Step Solution

1

Analyze the clinical presentation to identify the primary etiology of the patient's acute dyspnea.

The combination of orthopnea, severe hypertension, JVD, an S4 gallop, and radiographic evidence of peribronchial cuffing and septal lines strongly indicates acute decompensated heart failure (ADHF) with pulmonary edema.

Differentiating ADHF from a COPD exacerbation or pneumonia is critical because the presence of wheezing ('cardiac asthma') and a heavy smoking history can lead to diagnostic anchoring.

2

Interpret the laboratory and arterial blood gas (ABG) findings.

The normal procalcitonin rules out a bacterial pneumonia trigger. The ABG shows a pH of 7.28, PaCO2 of 55 mmHg, and normal HCO3-, confirming an acute respiratory acidosis due to impaired alveolar gas exchange from pulmonary edema.

Understanding the acid-base disturbance guides respiratory support; acute respiratory acidosis in ADHF is typically managed with noninvasive ventilation rather than bicarbonate or immediate intubation.

3

Determine the optimal multi-modality treatment for ADHF presenting with severe hypertension and respiratory failure.

Select intravenous loop diuretics (furosemide) for volume reduction, rapid-acting vasodilators (nitroglycerin) to reduce severe afterload, and noninvasive positive pressure ventilation (NIPPV) to treat the acute respiratory acidosis and hypoxia.

These interventions work synergistically to decrease left ventricular filling pressures, improve cardiac output, and recruit alveoli, rapidly reversing the pathophysiologic derangements.

Key Concept

Patients with acute decompensated heart failure can present with 'cardiac asthma' (wheezing due to peribronchial edema) and acute respiratory acidosis, requiring immediate management with loop diuretics, vasodilators, and noninvasive positive pressure ventilation.

Estimated Time:2m 0s

Question 763Question →

A 64-year-old woman is brought to the emergency department by her husband due to rapidly progressive confusion and a severe headache over the past 14 hours. She has a history of a deceased-donor renal transplant performed three years ago and is currently maintained on a regimen of tacrolimus, mycophenolate mofetil, and low-dose prednisone. On arrival, her temperature is 39.4°C (102.9°F), blood pressure is 98/60 mmHg, heart rate is 118/min, and respiratory rate is 24/min. Physical examination demonstrates marked nuchal rigidity. She is lethargic, oriented only to person, and withdraws appropriately from painful stimuli. Pupils are equal and reactive to light.

Arrange the following diagnostic and therapeutic steps in the most appropriate sequential order for the immediate management of this patient.

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Answer

The correct sequence is to first obtain peripheral blood cultures, immediately administer empiric antibiotics and corticosteroids, then perform a non-contrast head CT, and finally perform a lumbar puncture.

In patients with suspected bacterial meningitis who have contraindications to immediate lumbar puncture (e.g., altered mental status, new-onset seizures, focal neurologic deficits, age >60, or an immunocompromised state), the exact sequence of interventions is critical for survival. First, peripheral blood cultures must be drawn to maximize diagnostic yield. Immediately afterward, empiric antibiotics and dexamethasone must be administered. In this immunocompromised patient, the correct regimen includes ceftriaxone, vancomycin, and ampicillin (to cover Listeria monocytogenes). Life-saving therapy must NEVER be delayed for neuroimaging. After therapy is initiated, a non-contrast head CT is performed to rule out mass effect. Only after the CT confirms the absence of mass effect is a lumbar puncture performed for cerebrospinal fluid analysis.

Step-by-Step Solution

1

Recognize the clinical syndrome and assess indications for neuroimaging.

The patient has acute bacterial meningitis. Her immunocompromised state and altered mental status are absolute indications for obtaining a head CT before a lumbar puncture.

Performing a lumbar puncture blindly in a patient with potential elevated intracranial pressure can precipitate fatal cerebral herniation.

2

Sequence the most urgent therapeutic interventions.

Blood cultures are drawn first, followed immediately by empiric intravenous dexamethasone, ceftriaxone, vancomycin, and ampicillin.

Blood cultures must be obtained before antimicrobial administration to optimize pathogen recovery. However, antibiotics must not be delayed while waiting for a CT scan or lumbar puncture; early administration is the most important factor in reducing mortality. Ampicillin is included to cover Listeria monocytogenes due to her immunocompromised status.

3

Sequence the diagnostic neuroimaging and fluid analysis.

A non-contrast head CT is performed next, followed by a lumbar puncture.

The CT scan is necessary to rule out mass effect. Once safety is confirmed by the imaging, the lumbar puncture is performed to obtain cerebrospinal fluid for definitive diagnosis and antimicrobial tailoring.

Key Concept

Management sequence of acute bacterial meningitis in patients with contraindications to immediate lumbar puncture

Estimated Time:1m 30s

Question 764Question →

A 32-year-old man comes to the outpatient clinic reporting a 5-month history of worsening fatigue, cold intolerance, generalized weakness, and decreased libido. He struggles to concentrate at work and frequently takes naps during the day. Eight months ago, he was involved in a high-speed motor vehicle collision that resulted in a severe traumatic brain injury. His hospital course was complicated by increased intracranial pressure requiring a 3-week stay in the intensive care unit. He currently takes no medications. Vital signs show a blood pressure of $105/65$ mm Hg and a pulse of $58$ /min. Physical examination reveals a slow, deliberate speech pattern and delayed relaxation phase of the deep tendon reflexes. Visual fields are full to confrontation. Laboratory results are as follows:

Laboratory Test	Result	Reference Range
Thyroid-stimulating hormone (TSH)	$1.8$ µU/mL	$0.4-4.2$ µU/mL
Free thyroxine (T4)	$0.6$ ng/dL	$0.8-2.7$ ng/dL
Total testosterone	$145$ ng/dL	$300-1000$ ng/dL
Luteinizing hormone (LH)	$1.2$ mIU/mL	$1.5-9.3$ mIU/mL

Which of the following is the most likely underlying mechanism for this patient's current condition?

Shearing injury to the hypothalamic-pituitary structures

Lymphocytic infiltration of the thyroid gland parenchyma

Systemic down-regulation of peripheral thyroid hormone conversion

Antibody-mediated inflammation of the anterior pituitary gland

Primary failure of the Leydig cells with concurrent glandular atrophy

Show answer & explanation

Answer: Shearing injury to the hypothalamic-pituitary structures

Answer

The correct answer is shearing injury to the hypothalamic-pituitary structures, which describes post-traumatic hypopituitarism.

The correct answer identifies the mechanical etiology of this patient's combined endocrinopathies. The laboratory findings of low target-gland hormones (T4, testosterone) without the expected elevation in pituitary stimulating hormones (TSH, LH) definitively point to central pituitary failure. Given his history of severe traumatic brain injury, the most likely mechanism is post-traumatic hypopituitarism caused by mechanical shearing of the pituitary stalk or damage to the hypothalamic-pituitary portal circulation.

Step-by-Step Solution

1

Analyze the thyroid function tests.

The free T4 is low (

0.6

ng/dL), but the TSH is within the normal range (

1.8

µU/mL) instead of being elevated.

This 'inappropriately normal' TSH in the setting of low T4 establishes the diagnosis of central (secondary) hypothyroidism.

2

Analyze the gonadal hormone panel.

Total testosterone is clearly low (

145

ng/dL), and the LH is inappropriately normal/low (

1.2

mIU/mL).

A low testosterone should stimulate high LH production. The failure to mount an LH response confirms central (secondary) hypogonadism.

3

Integrate the laboratory findings with the patient's clinical history.

The patient has multi-axis central pituitary failure (panhypopituitarism) following a severe traumatic brain injury 8 months ago.

Moderate to severe traumatic brain injury often causes mechanical shearing forces on the pituitary stalk or ischemic necrosis of the hypothalamic-pituitary vascular supply, leading to post-traumatic hypopituitarism months or even years after the initial insult.

Key Concept

Post-traumatic hypopituitarism is a common complication of severe traumatic brain injury, presenting months to years later with central deficiencies such as central hypothyroidism (low T4, normal/low TSH) and central hypogonadism (low testosterone, normal/low LH) due to mechanical shearing of the pituitary stalk.

Estimated Time:1m 30s

Question 765Question →

In the evaluation of patients with suspected idiopathic inflammatory myopathies, specific autoantibody profiles offer critical prognostic information regarding disease progression, expected complications, and treatment response. Match each myositis-specific autoantibody to its most characteristic clinical phenotype.

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Answer

Anti-Jo-1 pairs with antisynthetase syndrome (fever, arthritis, ILD, mechanic's hands). Anti-MDA5 pairs with amyopathic dermatomyositis and rapidly progressive ILD. Anti-TIF1-gamma pairs with malignancy-associated dermatomyositis. Anti-SRP pairs with severe immune-mediated necrotizing myopathy.

Each myositis-specific autoantibody is strongly linked to a distinct clinical phenotype that guides prognosis and management. Recognizing these associations is critical: Anti-Jo-1 defines antisynthetase syndrome; Anti-MDA5 flags life-threatening rapidly progressive ILD; Anti-TIF1-gamma warns of underlying malignancy; and Anti-SRP indicates severe immune-mediated necrotizing myopathy.

Step-by-Step Solution

1

Evaluate Anti-Jo-1

Matched to the phenotype with non-erosive polyarthritis, interstitial lung disease, and hyperkeratotic skin.

Anti-Jo-1 is the prototypical antibody for antisynthetase syndrome, classically presenting with 'mechanic's hands' and pulmonary involvement.

2

Evaluate Anti-MDA5

Matched to amyopathic dermatomyositis with rapid interstitial lung disease.

Anti-MDA5 is notorious for causing minimal muscle involvement but devastating, rapidly progressive interstitial lung disease and deep skin ulcers.

3

Evaluate Anti-TIF1-gamma

Matched to classic dermatomyositis with an elevated risk of internal malignancy.

The presence of Anti-TIF1-gamma is a major red flag for paraneoplastic dermatomyositis in adults, requiring extensive cancer screening.

4

Evaluate Anti-SRP

Matched to severe, acute-onset necrotizing myopathy.

Anti-SRP signifies a necrotizing process rather than classical inflammation, leading to massive CK elevations, severe weakness, and potential cardiac involvement.

Key Concept

Myositis-specific autoantibodies and their defining clinical phenotypes

Question 766Question →

An antimicrobial stewardship team is auditing the appropriateness of targeted therapies for various complex infections. Match each specific patient scenario and pathogen profile below with its single most appropriate targeted treatment strategy based on current clinical guidelines.

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Answer

Each clinical scenario is matched with its definitive guideline-recommended targeted therapy, factoring in specific resistance patterns, allergies, and patient characteristics.

Each matching pair correctly aligns a complex infectious disease scenario with its definitive, guideline-supported treatment exception. The pregnant patient with syphilis requires penicillin desensitization. The patient with HLAR Enterococcus endocarditis requires dual beta-lactam therapy (ampicillin and ceftriaxone). The penicillin-allergic patient with Listeria requires trimethoprim-sulfamethoxazole. The patient with invasive aspergillosis requires voriconazole.

Step-by-Step Solution

1

Evaluate the syphilis patient who is pregnant and has a penicillin allergy.

Identify that penicillin is mandatory to prevent congenital syphilis, requiring desensitization.

Alternative treatments are either harmful to the fetus or do not achieve adequate transplacental levels.

2

Evaluate the patient with E. faecalis endocarditis and high-level aminoglycoside resistance (HLAR).

Identify ampicillin plus ceftriaxone as the appropriate regimen.

HLAR precludes the use of gentamicin for synergy; dual beta-lactam therapy is the proven synergistic alternative.

3

Evaluate the patient with Listeria meningitis and a severe beta-lactam allergy.

Identify trimethoprim-sulfamethoxazole as the treatment of choice.

Listeria is intrinsically resistant to cephalosporins, and alternative agents like vancomycin are ineffective. TMP-SMX is bactericidal and penetrates the CSF well.

4

Evaluate the neutropenic patient with a halo sign on chest CT and positive galactomannan.

Identify voriconazole as the appropriate treatment.

The findings are pathognomonic for invasive pulmonary aspergillosis, for which voriconazole is the first-line agent.

Key Concept

Targeted antimicrobial therapy for complex systemic infections requires specific deviations from standard therapy based on patient factors (e.g., pregnancy, severe allergies) and specific pathogen resistance mechanisms.

Estimated Time:2m 0s

Question 767Question →

Match each clinical scenario describing a medication-induced renal, electrolyte, or acid-base abnormality to the corresponding causative pharmacological agent.

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Answer

The correct pairings identify Trimethoprim-sulfamethoxazole for the isolated creatinine elevation with hyperkalemia, Amphotericin B for the Type 1 RTA presentation, Acetazolamide for the Type 2 RTA presentation, and Lithium carbonate for the nephrogenic diabetes insipidus presentation.

Each pharmacological agent possesses a distinct pathophysiological mechanism affecting the renal tubules: Trimethoprim blocks both creatinine secretion and ENaC channels; Amphotericin B creates pores in the distal tubule causing a Type 1 RTA; Acetazolamide inhibits proximal carbonic anhydrase causing a Type 2 RTA; and Lithium induces ADH resistance at the collecting duct, causing nephrogenic DI.

Step-by-Step Solution

1

Analyze the scenario with isolated creatinine rise and hyperkalemia but normal eGFR.

Identifies tubular secretion blockade and distal ENaC inhibition, consistent with trimethoprim-sulfamethoxazole use.

Differentiating pseudo-renal failure from true acute kidney injury is essential when managing patients on specific antimicrobials.

2

Evaluate the non-anion gap metabolic acidosis accompanied by severe hypokalemia and a high urine pH (> 5.5).

Classifies the disorder as Type 1 (distal) renal tubular acidosis, a known toxicity of amphotericin B.

The inability to excrete hydrogen ions distally results in an inappropriately alkaline urine despite systemic acidosis.

3

Evaluate the non-anion gap metabolic acidosis with intact distal acidification (urine pH < 5.5).

Identifies Type 2 (proximal) renal tubular acidosis, an expected effect of acetazolamide therapy.

Acetazolamide wastes bicarbonate proximally, but because the distal tubule is unharmed, the urine can eventually be acidified.

4

Analyze the ADH-resistant polyuria and hypernatremia.

Confirms a diagnosis of nephrogenic diabetes insipidus, which is a classic adverse effect of chronic lithium therapy.

The lack of response to exogenous desmopressin localizes the defect to the renal collecting duct rather than central ADH release.

Key Concept

Pathophysiology and identification of drug-induced nephrotoxicity and distinct acid-base/electrolyte derangements.

Question 768Question →

A 72-year-old woman presents to the emergency department with a 2-day history of right-sided temporal headache, jaw pain with chewing, and scalp tenderness. This morning, she experienced a 10-minute episode of painless visual loss in her right eye that has since resolved. Her temperature is $37.6^\circ\text{C}$ ( $99.7^\circ\text{F}$ ), blood pressure is $130/80\text{ mmHg}$ , and pulse is $84/\text{min}$ . Physical examination reveals a prominent, tender right temporal artery with diminished pulsation. Laboratory studies show an erythrocyte sedimentation rate (ESR) of $105\text{ mm/h}$ . Arrange the following management steps in the most appropriate chronological sequence for this patient.

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Answer

The correct sequence is: Administer high-dose intravenous methylprednisolone, then perform a temporal artery biopsy, then transition to high-dose oral prednisone, and finally initiate a gradual glucocorticoid taper.

The patient's presentation is classic for giant cell arteritis (GCA) complicated by transient ischemic vision loss (amaurosis fugax). Because GCA can cause rapid, irreversible blindness via anterior ischemic optic neuropathy, the absolute first priority is to administer high-dose intravenous methylprednisolone. Corticosteroids must never be delayed for diagnostic testing. Once therapy is initiated, a temporal artery biopsy should be performed (usually within 1 to 2 weeks) to confirm the diagnosis, as the histologic signs of arteritis remain present for several days to weeks after starting steroids. Following a short course of intravenous therapy, the patient is transitioned to high-dose oral prednisone. Finally, once clinical symptoms have completely resolved and the ESR has normalized, a very gradual tapering of the oral steroids is initiated over several months to minimize steroid-induced adverse effects while preventing disease relapse.

Step-by-Step Solution

1

Identify the primary diagnosis and its severity based on the clinical presentation.

The patient has giant cell arteritis complicated by amaurosis fugax (transient vision loss), which is an acute ischemic complication.

Recognizing ischemic complications dictates the urgency and route of corticosteroid administration.

2

Determine the immediate next best step in management.

Administer intravenous methylprednisolone.

Immediate high-dose IV steroids are required to prevent permanent blindness. Delaying treatment for diagnostic testing is contraindicated.

3

Determine the timing of the definitive diagnostic test.

Perform a temporal artery biopsy.

Biopsy is the gold standard and should be done within 1-2 weeks of starting steroids, as diagnostic histologic features persist during early treatment.

4

Identify the long-term management strategy.

Transition to oral prednisone, followed eventually by a gradual taper.

IV steroids are typically given for a short duration, followed by oral maintenance. Once symptoms and ESR normalize, a slow taper prevents both steroid toxicity and disease relapse.

Key Concept

In giant cell arteritis with ischemic complications (e.g., vision changes), immediate high-dose intravenous corticosteroids are required to prevent blindness, taking precedence over obtaining a temporal artery biopsy.

Question 769Question →

A 19-year-old male college student is brought to the emergency department by paramedics after experiencing a generalized tonic-clonic seizure that lasted 2 minutes. His roommate reports that the patient had complained of a severe headache, nausea, and high fever for the past 12 hours. His temperature is $39.6^\circ\text{C}$ ( $103.3^\circ\text{F}$ ), blood pressure is $98/60$ mmHg, and heart rate is $124$ /min. On physical examination, the patient is lethargic, postictal, and mildly confused. Pronounced nuchal rigidity is present. A non-blanching petechial rash is observed on his bilateral lower extremities.

Arrange the following next steps in management in the most appropriate chronological order for this patient.

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Answer

The correct sequence is to first obtain blood cultures, immediately administer empiric intravenous antibiotics and dexamethasone, perform a non-contrast head CT scan, and finally perform a lumbar puncture.

The standard of care for suspected bacterial meningitis requires the rapid initiation of therapy. While a lumbar puncture (LP) is the definitive diagnostic test, certain patients are at high risk for cerebral herniation and require a head CT before the LP. The Infectious Diseases Society of America (IDSA) guidelines require a CT before LP in patients with immunocompromise, a history of CNS disease, new-onset seizures, papilledema, altered level of consciousness, or focal neurologic deficits. Because this patient has a new-onset seizure and altered mental status, the sequence must be: 1) Blood cultures, 2) Empiric antibiotics and dexamethasone, 3) Head CT, and 4) Lumbar puncture. This guarantees that life-saving treatment is not delayed by the time required to obtain and interpret neuroimaging.

Step-by-Step Solution

1

Recognize the clinical presentation and identify 'red flag' indications.

The patient has signs of bacterial meningitis (fever, headache, nuchal rigidity, petechial rash) along with indications for a head CT before LP (new-onset seizure and altered mental status).

Identifying red flags dictates the diagnostic and therapeutic pathway, specifically indicating the need for neuroimaging before safely accessing the subarachnoid space.

2

Determine the first immediate action upon arrival.

Obtain blood cultures.

Blood cultures are rapid and should always be drawn prior to the administration of any antimicrobials to ensure the highest yield for identifying the causative pathogen.

3

Decide the timing of empiric antimicrobial therapy.

Administer empiric intravenous antibiotics and dexamethasone immediately.

Because the patient must go to the CT scanner before the LP, definitive CSF evaluation will be delayed. To prevent mortality and neurologic deficits, empiric therapy must be given immediately after blood cultures, without waiting for the CT or LP results.

4

Determine the sequence of imaging and invasive testing.

Perform a non-contrast head CT, followed by a lumbar puncture.

The CT scan is necessary to rule out mass lesions and prevent cerebral herniation. Once mass effect is ruled out, the LP is performed to obtain CSF for definitive analysis.

Key Concept

In patients with suspected bacterial meningitis who have indications for a head CT prior to lumbar puncture (e.g., new-onset seizure, altered mental status, papilledema, immunocompromise), empiric antibiotics and dexamethasone must be administered immediately after blood cultures are drawn, before sending the patient for imaging.

Question 770Question →

An internal medicine team is evaluating a $67$ -year-old male who presented to the emergency department with a $5$ -day history of progressively worsening shortness of breath, orthopnea, and lower extremity swelling. His medical history includes seropositive rheumatoid arthritis, for which infliximab was added to his methotrexate regimen $4$ months ago due to refractory joint pain. He also has a $35$ -pack-year smoking history. On physical examination, his temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $112/74\text{ mm Hg}$ , heart rate is $110\text{ /min}$ , and respiratory rate is $24\text{ /min}$ . Pulse oximetry shows $91\%$ on ambient air. Jugular venous distention is prominent at $45$ degrees. Chest auscultation reveals bilateral basilar crackles and a prominent third heart sound (S3). There is $2+$ bilateral pitting edema extending to the knees. Joint examination shows no active synovitis, warmth, or effusions. Which of the following is the most appropriate next step in the pharmacologic management of this patient's current condition?

Administer nebulized albuterol and oral prednisone

Initiate intravenous vancomycin and piperacillin-tazobactam

Discontinue infliximab and administer intravenous furosemide

Discontinue methotrexate and administer leucovorin

Measure serum thyroid-stimulating hormone and free thyroxine levels

Show answer & explanation

Answer: Discontinue infliximab and administer intravenous furosemide

Answer

Discontinue infliximab and administer intravenous furosemide

The correct action is to discontinue the tumor necrosis factor-alpha (TNF-alpha) inhibitor and administer a loop diuretic. This patient presents with classic signs of acute decompensated heart failure, including orthopnea, jugular venous distention, an S3 gallop, pulmonary crackles, and peripheral edema. TNF-alpha inhibitors (e.g., infliximab, etanercept, adalimumab) are known to precipitate new-onset heart failure or exacerbate underlying cardiac dysfunction. They are strictly contraindicated in patients with moderate to severe heart failure. Therefore, the essential next step is to immediately stop the offending medication and administer intravenous furosemide to manage the severe volume overload.

Step-by-Step Solution

1

Identify the primary clinical syndrome based on the physical examination findings.

The patient exhibits jugular venous distention, an S3 gallop, bilateral basilar crackles, and pitting edema, which establish a diagnosis of acute decompensated heart failure (ADHF).

Differentiating between cardiac, pulmonary, and infectious causes of acute dyspnea is the critical first step in determining management.

2

Determine the most likely precipitating cause of the heart failure in this specific patient.

The recent initiation of infliximab is the most likely trigger, as tumor necrosis factor-alpha (TNF-alpha) inhibitors are a known cause of new-onset or worsening heart failure.

Identifying medication-induced complications is essential in patients on complex immunosuppressive regimens to prevent ongoing toxicity.

3

Select the appropriate pharmacologic management based on the diagnosis and precipitant.

Discontinuation of the offending agent (infliximab) and initiation of a loop diuretic (intravenous furosemide) for symptomatic relief of volume overload.

ADHF requires immediate volume offloading, and the precipitating cardiotoxic medication must be stopped immediately.

Key Concept

Tumor necrosis factor-alpha (TNF-alpha) inhibitors can precipitate or exacerbate heart failure and should be discontinued if a patient develops signs of acute decompensated heart failure.

Question 771Question →

A 32-year-old man is admitted to the hospital with a 1-week history of fever, chills, and profound fatigue. He has a history of intravenous drug use and was treated for a skin abscess two months ago. His temperature is 38.8°C (101.8°F), blood pressure is 110/70 mm Hg, and pulse is 108/min. Physical examination reveals a new grade 3/6 holosystolic murmur best heard at the cardiac apex. Transesophageal echocardiography demonstrates a 1.2-cm mobile vegetation on the mitral valve. Three sets of blood cultures obtained on admission grow *Enterococcus faecalis* that is susceptible to ampicillin, vancomycin, gentamicin, and linezolid. The patient is initiated on continuous intravenous ampicillin and every-8-hour intravenous gentamicin. Over the next 48 hours, his clinical symptoms improve and his temperature decreases to 37.9°C (100.2°F). However, laboratory studies show his serum creatinine has increased from 0.8 mg/dL on admission to 2.5 mg/dL, and his urine output has been 350 mL over the past 24 hours. Which of the following is the most appropriate modification to this patient's antimicrobial regimen?

Discontinue gentamicin and add intravenous ceftriaxone

Discontinue gentamicin and continue ampicillin monotherapy

Discontinue the current regimen and initiate intravenous vancomycin

Discontinue the current regimen and initiate intravenous linezolid

Continue the current regimen and adjust the gentamicin dose based on serum trough levels

Show answer & explanation

Answer: Discontinue gentamicin and add intravenous ceftriaxone

Answer

Discontinue gentamicin and add intravenous ceftriaxone

The most appropriate modification to this patient's regimen is to discontinue gentamicin and add intravenous ceftriaxone. This patient has *Enterococcus faecalis* infective endocarditis and has developed severe acute kidney injury (AKI) secondary to gentamicin toxicity. Enterococci are intrinsically tolerant to the bactericidal effects of cell-wall active agents (like penicillins) when used alone. To achieve the bactericidal activity required to cure endocarditis, synergistic combination therapy is necessary. The standard first-line regimens are ampicillin plus an aminoglycoside (e.g., gentamicin) or ampicillin plus ceftriaxone. Although ceftriaxone has no clinically significant activity against enterococci on its own, it saturates specific penicillin-binding proteins (PBPs, primarily PBP 2 and 3), which works synergistically with ampicillin (which binds PBP 4) to provide bactericidal activity. Because the ampicillin plus ceftriaxone regimen is equally effective as ampicillin plus gentamicin but entirely avoids aminoglycoside-associated nephrotoxicity, it is the treatment of choice for *E. faecalis* endocarditis in patients who develop AKI during therapy or those with preexisting renal dysfunction.

Step-by-Step Solution

1

Identify the patient's primary diagnosis and current clinical status.

The patient has Enterococcus faecalis infective endocarditis and has developed oliguric acute kidney injury (AKI) while receiving ampicillin and gentamicin.

Establishing the current complication is necessary to determine the appropriate next step in management.

2

Evaluate the current antimicrobial regimen's role in the patient's complication.

Gentamicin is a well-known nephrotoxic agent and is the most likely cause of the acute kidney injury.

Identifying the offending agent allows for targeted modification of the regimen.

3

Determine the optimal alternative therapy that maintains efficacy while avoiding further toxicity.

Substituting ceftriaxone for gentamicin provides the necessary bactericidal synergy against E. faecalis without causing further nephrotoxicity.

Endocarditis requires bactericidal therapy, and the ampicillin-ceftriaxone combination achieves this synergy through complementary binding of penicillin-binding proteins.

Key Concept

Management of Enterococcus faecalis infective endocarditis in the setting of aminoglycoside-induced acute kidney injury.

Question 772Question →

A 22-year-old man presents to the emergency department with a 2-day history of worsening nausea, diffuse abdominal pain, and profound fatigue. He has been excessively thirsty and urinating frequently. He has no significant past medical history. His temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $98/60\text{ mmHg}$ , heart rate is $118/\text{min}$ , and respiratory rate is $24/\text{min}$ with deep, rapid breaths. Mucous membranes are dry. The abdomen is diffusely tender but soft without rebound. Point-of-care testing reveals a capillary blood glucose of $480\text{ mg/dL}$ and large blood ketones. An arterial blood gas shows a pH of $7.18$ . The patient is diagnosed with an acute endocrine emergency.

Arrange the following management steps in the most appropriate algorithmic sequence for the acute stabilization and definitive therapy of this patient.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence for managing Diabetic Ketoacidosis is: 1) Administer intravenous isotonic crystalloid, 2) Assess serum potassium, 3) Initiate intravenous regular insulin, 4) Add dextrose to intravenous fluids when glucose falls to

200\text{-}250\text{ mg/dL}

, and 5) Transition to subcutaneous insulin once the anion gap is closed.

The exact algorithmic sequence for DKA ensures physiological safety. Fluid resuscitation immediately addresses life-threatening hypovolemia. Assessing potassium ensures insulin can be given safely without precipitating lethal arrhythmias. Insulin stops the underlying pathophysiology (ketogenesis). Adding dextrose prevents iatrogenic hypoglycemia while the insulin finishes clearing the acid load. Finally, transitioning to subcutaneous insulin represents the resolution of the acute crisis and return to maintenance therapy.

Step-by-Step Solution

1

Synthesize the clinical diagnosis based on the vignette.

The patient is experiencing Diabetic Ketoacidosis (DKA).

The clinical presentation of polyuria, polydipsia, abdominal pain, Kussmaul respirations, profound hyperglycemia (

480\text{ mg/dL}

), ketonemia, and severe metabolic acidosis (pH

7.18

) is diagnostic of DKA.

2

Determine the highest priority in acute stabilization.

Aggressive fluid resuscitation with

0.9\%

normal saline.

Patients with DKA have profound osmotic diuresis leading to severe total body water deficits (often

5\text{-}8\text{ L}

). Restoring intravascular volume is the absolute first step to prevent cardiovascular collapse and acute renal failure.

3

Identify the prerequisite safety check before starting specific medical therapy.

Check the serum potassium level.

Patients with DKA often have total body potassium depletion despite normal or high serum levels. Insulin drives potassium intracellularly. If baseline potassium is

<3.3\text{ mEq/L}

, insulin must be withheld until potassium is replaced to avoid lethal arrhythmias.

4

Establish the sequence of medication administration and subsequent fluid adjustment.

Start an intravenous regular insulin infusion, then add

5\%

dextrose when glucose reaches

200\text{ mg/dL}

.

Insulin is required to suppress lipolysis and resolve the ketoacidosis. Once glucose levels drop significantly, dextrose is added to prevent hypoglycemia while allowing the continuous insulin infusion to finish closing the anion gap.

5

Determine the criteria for transitioning to maintenance therapy.

Switch to subcutaneous insulin.

Once the anion gap closes, acidosis resolves, and the patient can eat, an overlapping transition to subcutaneous basal-bolus insulin is performed.

Key Concept

The algorithmic management of Diabetic Ketoacidosis requires strict sequential therapy: aggressive fluid resuscitation, potassium assessment prior to insulin initiation, fluid modification with dextrose, and eventual transition to subcutaneous insulin once the anion gap closes.

Question 773Question →

During morning rounds, a $58$ -year-old male inpatient is evaluated on postoperative day $7$ following an open partial gastrectomy for gastric adenocarcinoma. The patient reports new-onset severe right calf pain and swelling that began earlier this morning, along with mild shortness of breath. His medications include pantoprazole and subcutaneous unfractionated heparin, which was started postoperatively for venous thromboembolism prophylaxis. Temperature is $37.8^\circ \text{C}$ ( $100.0^\circ \text{F}$ ), blood pressure is $135/85 \text{ mmHg}$ , pulse is $105/\text{min}$ , and respirations are $18/\text{min}$ . Pulse oximetry shows $96\%$ on room air. Physical examination reveals a swollen, erythematous, and tender right calf. Lungs are clear to auscultation bilaterally.

Complete laboratory panel shows:

Laboratory Test	Result
Hemoglobin	$11.2 \text{ g/dL}$
Leukocyte count	$8,500/\mu\text{L}$
Platelet count	$105,000/\mu\text{L}$ (Baseline prior to surgery: $240,000/\mu\text{L}$ )
Serum creatinine	$1.1 \text{ mg/dL}$
Prothrombin time	$12 \text{ seconds}$
Activated partial thromboplastin time	$32 \text{ seconds}$

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

Discontinue unfractionated heparin and initiate argatroban

Discontinue unfractionated heparin and initiate enoxaparin

Obtain a lower extremity venous duplex ultrasound and continue current medications

Administer a pool of donor platelets

Obtain blood cultures and initiate intravenous vancomycin and piperacillin-tazobactam

Show answer & explanation

Answer: Discontinue unfractionated heparin and initiate argatroban

Answer

The correct answer is to discontinue unfractionated heparin and initiate a non-heparin anticoagulant such as argatroban.

This patient's clinical presentation is highly suspicious for type 2 Heparin-Induced Thrombocytopenia (HIT) complicated by a new deep vein thrombosis (DVT). The diagnosis of HIT is assessed using the '4 T's' score, which evaluates Timing (typically

5

-

10

days after heparin exposure), Thrombocytopenia (a greater than

50\%

drop from baseline), Thrombosis (new venous or arterial clots), and the absence of oTher causes. This patient meets the criteria for a high-probability score (day

7

,

>50\%

platelet drop, and a new DVT). The immediate, life-saving next step in management is to strictly discontinue all heparin exposure (including line flushes) and immediately initiate therapeutic anticoagulation with a non-heparin agent, such as a direct thrombin inhibitor (e.g., argatroban) or fondaparinux, to prevent further massive thrombosis.

Step-by-Step Solution

1

Calculate the patient's '4 T's' score for Heparin-Induced Thrombocytopenia (HIT).

The patient has appropriate Timing (day 7 of therapy), significant Thrombocytopenia (drop from 240,000 to 105,000, which is >50%), and a new Thrombosis (clinical symptoms of DVT), making HIT highly probable.

Recognizing the clinical triad of heparin exposure, platelet drop, and new thrombosis is required to correctly diagnose HIT.

2

Determine the immediate management for high-probability HIT.

All heparin products must be stopped immediately. Waiting for confirmatory laboratory testing (e.g., serotonin release assay) is inappropriate.

Continued exposure to heparin will worsen the hypercoagulable state and lead to severe complications like pulmonary embolism or limb ischemia.

3

Select the appropriate alternative therapy.

Therapeutic anticoagulation with a non-heparin agent (e.g., direct thrombin inhibitors like argatroban or bivalirudin, or fondaparinux) must be initiated.

Anticoagulation is required because HIT is a highly prothrombotic state. Low-molecular-weight heparins (like enoxaparin) cannot be used due to cross-reactivity.

Key Concept

Diagnosis and acute management of Heparin-Induced Thrombocytopenia (HIT)

Question 774Question →

A male patient, aged $48$ , presents to an ambulatory care facility reporting a $6$ -week history of a persistent cough and episodes of blood-tinged sputum. Over this same period, he has experienced recurrent nosebleeds, intermittent low-grade fevers, and profound fatigue. His medical history includes major depressive disorder, for which he has been taking citalopram for the last $3$ years. He does not smoke or use illicit drugs.

Vital signs show a temperature of $37.7^\circ\text{C}$ ( $99.9^\circ\text{F}$ ), blood pressure of $152/96\text{ mm Hg}$ , heart rate of $88/\text{min}$ , and respiratory rate of $16/\text{min}$ .

Examination of the nasal cavity reveals mucosal ulcerations and adherent crusts. Auscultation of the lungs demonstrates scattered crackles in the right middle lung field.

Laboratory studies reveal:
Hemoglobin: $10.2\text{ g/dL}$
Leukocyte count: $11,500/\text{mm}^3$
Blood urea nitrogen: $34\text{ mg/dL}$
Serum creatinine: $2.2\text{ mg/dL}$ (was $0.8\text{ mg/dL}$ during a routine checkup $8$ months ago)
Urinalysis: $2+$ protein, large blood, $>50\text{ red blood cells/hpf}$ , and several red blood cell casts.

A radiograph of the chest demonstrates a $3.5\text{-cm}$ cavitary lesion in the right middle lobe with thick walls.

Based on the most likely diagnosis, which of the following is the most appropriate next step in evaluation or management?

Measurement of serum autoantibodies against proteinase-3 and myeloperoxidase

Empiric treatment with intravenous clindamycin and ceftriaxone

Administration of intravenous furosemide and noninvasive positive pressure ventilation

Immediate cessation of the patient's selective serotonin reuptake inhibitor

Assessment of serum thyrotropin and free thyroxine levels

Show answer & explanation

Answer: Measurement of serum autoantibodies against proteinase-3 and myeloperoxidase

Answer

Measurement of serum autoantibodies against proteinase-3 and myeloperoxidase

The correct answer is the measurement of serum autoantibodies against proteinase-3 and myeloperoxidase. This patient presents with the classic triad of Granulomatosis with Polyangiitis (GPA): upper respiratory tract disease (recurrent epistaxis, nasal ulcerations/crusting), lower respiratory tract disease (cough, hemoptysis, cavitary lung lesion), and glomerulonephritis (hypertension, elevated creatinine, hematuria, and red blood cell casts). GPA is an ANCA-associated small-vessel vasculitis. The most appropriate initial non-invasive step in the diagnostic workup is testing for anti-neutrophil cytoplasmic antibodies (ANCA). Approximately 90% of patients with active systemic GPA will test positive for c-ANCA (which targets proteinase-3, or PR3). Once seropositivity is confirmed, a tissue biopsy (typically from the kidney or upper airway) is obtained for definitive diagnosis.

Step-by-Step Solution

1

Analyze the clinical triad of symptoms

The patient exhibits upper respiratory tract involvement (epistaxis, nasal mucosal ulcerations), lower respiratory tract involvement (hemoptysis, cavitary lung lesion), and renal involvement (acute kidney injury with red blood cell casts indicating glomerulonephritis).

Identifying the pattern of organ involvement is crucial for recognizing specific systemic vasculitides.

2

Formulate the most likely diagnosis

The combination of this triad is highly characteristic of Granulomatosis with Polyangiitis (GPA, formerly Wegener's granulomatosis).

GPA uniquely causes necrotizing granulomatous inflammation affecting these three distinct vascular beds.

3

Determine the best initial diagnostic step

Serologic testing for anti-neutrophil cytoplasmic antibodies (ANCA), specifically PR3-ANCA and MPO-ANCA.

While a tissue biopsy (often nasal or renal) is required for definitive confirmation, ANCA testing is the most appropriate, rapid, and non-invasive initial step to support the diagnosis and guide urgent immunosuppressive therapy.

Key Concept

The classic presentation and initial diagnosis of Granulomatosis with Polyangiitis (GPA)

Estimated Time:1m 15s

Question 775Question →

A 32-year-old woman with a history of systemic lupus erythematosus and recurrent kidney stones is evaluated in the clinic for progressive, generalized muscle weakness over the past two weeks. She reports difficulty climbing stairs and rising from a seated position. She denies diarrhea, vomiting, fever, or recent illnesses. Her vital signs are within normal limits. Physical examination reveals symmetric proximal muscle weakness in the bilateral lower extremities with diminished deep tendon reflexes.

Laboratory evaluation shows the following:

Serum chemistry:
Sodium: 140 mEq/L
Potassium: 2.6 mEq/L
Chloride: 114 mEq/L
Bicarbonate: 14 mEq/L
Blood urea nitrogen: 16 mg/dL
Creatinine: 0.9 mg/dL

Arterial blood gas (room air):
pH: 7.26
pCO2: 29 mm Hg
pO2: 96 mm Hg

Urinalysis reveals a pH of 6.8 with no protein or blood.

Based on the provided laboratory data, which of the following statements is most accurate regarding this patient's current acid-base physiological state?

The respiratory system has appropriately responded to a primary loss of serum buffering capacity.

The patient exhibits an inappropriate degree of hyperventilation, indicating a superimposed primary respiratory disorder.

The accumulation of unmeasured endogenous anions is the primary driver of the acidemia.

The measured arterial carbon dioxide level reflects the primary mechanism of the acid-base disturbance.

The arterial blood gas reveals an inadequate ventilatory response, indicating a concomitant respiratory acidosis.

Show answer & explanation

Answer: The respiratory system has appropriately responded to a primary loss of serum buffering capacity.

Answer

The respiratory system has appropriately responded to a primary loss of serum buffering capacity.

The patient's laboratory results demonstrate an acidemic pH driven by low bicarbonate, confirming a primary metabolic acidosis (loss of serum buffers). The anion gap is normal (

12

mEq/L). To assess respiratory compensation, Winter's formula is applied:

\text{Expected pCO}_2 = 1.5 \times 14 + 8 = 29

(range

27-31

mm Hg). Because the patient's actual pCO2 is

29

mm Hg, the respiratory system has mounted a completely appropriate physiological response.

Step-by-Step Solution

1

Evaluate the arterial pH to determine the primary direction of the disturbance.

The pH is 7.26, which is strictly acidemic (normal 7.35 - 7.45).

Establishing acidemia helps differentiate whether subsequent abnormalities are primary drivers or compensatory mechanisms.

2

Examine the serum bicarbonate and pCO2 to identify the primary etiology.

The serum bicarbonate is significantly low at 14 mEq/L, which aligns with the acidemic pH. This indicates a primary metabolic acidosis (loss of serum buffering capacity).

The primary disorder must match the direction of the pH shift.

3

Calculate the serum anion gap to characterize the metabolic acidosis.

\text{Anion Gap} = \text{Na}^+ - (\text{Cl}^- + \text{HCO}_3^-) = 140 - (114 + 14) = 12

mEq/L. This is a normal anion gap.

Differentiating between normal and high anion gap metabolic acidosis is crucial for diagnosing the underlying disease (e.g., Renal Tubular Acidosis vs. Lactic Acidosis).

4

Apply Winter's formula to determine if the respiratory compensation is appropriate.

\text{Expected pCO}_2 = (1.5 \times \text{HCO}_3^-) + 8 \pm 2 = (1.5 \times 14) + 8 \pm 2 = 29 \pm 2

mm Hg. The actual pCO2 is exactly 29 mm Hg.

If the measured pCO2 falls within the calculated expected range, the patient has an appropriately compensated simple metabolic acidosis without any superimposed respiratory disorders.

Key Concept

The physiological diagnosis of a simple, compensated normal anion gap metabolic acidosis requires calculating the anion gap and confirming the adequacy of respiratory compensation using Winter's formula.

Question 776Question →

Match each clinical vignette describing a systemic fungal infection with the most appropriate first-line pharmacotherapy.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Mild-to-moderate blastomycosis is matched with oral itraconazole; Disseminated histoplasmosis is matched with intravenous liposomal amphotericin B followed by oral itraconazole; Cryptococcal meningoencephalitis is matched with intravenous liposomal amphotericin B plus oral flucytosine; Invasive pulmonary aspergillosis is matched with intravenous voriconazole.

Each fungal infection dictates a highly specific regimen. Mild blastomycosis is successfully treated with itraconazole. Disseminated histoplasmosis demands amphotericin B induction followed by itraconazole maintenance. Cryptococcal meningitis requires synergistic amphotericin B and flucytosine to clear the CNS. Invasive aspergillosis uniquely requires the mold-active triazole voriconazole.

Step-by-Step Solution

1

Analyze the first vignette to determine the pathogen and disease severity.

Broad-based budding yeasts in a stable patient from Wisconsin indicates mild-to-moderate blastomycosis, which responds well to oral triazoles.

Accurate pathogen identification and severity stratification dictate whether oral or intravenous antifungal therapy is required.

2

Analyze the second vignette for pathogen morphology and clinical status.

Intracellular yeasts in macrophages with hepatosplenomegaly in an HIV patient indicates progressive disseminated histoplasmosis, requiring aggressive two-step therapy.

Disseminated endemic mycoses in severely immunocompromised hosts are fatal without rapid, broad fungicidal induction.

3

Evaluate the third vignette based on CSF findings.

Encapsulated yeasts in CSF with high opening pressure indicates cryptococcal meningitis, necessitating combination therapy that penetrates the blood-brain barrier.

CNS fungal infections require specific regimens optimized for rapid CSF sterilization to prevent mortality.

4

Interpret the fourth vignette's radiologic and hematologic clues.

A prolonged neutropenic patient with hemoptysis and a CT halo sign has invasive pulmonary aspergillosis, requiring targeted mold-active therapy.

Aspergillus is an angioinvasive mold; its treatment fundamentally differs from yeast infections.

Key Concept

Definitive Pharmacotherapy for Systemic Fungal Infections based on Pathogen and Disease Severity

Question 777Question →

Emergency medical services transport a $65$ -year-old man from a long-term care facility to the hospital due to acute-onset confusion, fever, and severe abdominal pain. His past medical history is significant for alcohol-associated cirrhosis with refractory ascites, which is managed with high-dose furosemide and spironolactone. Upon arrival, his temperature is $39.2^\circ$ C ( $102.6^\circ$ F), blood pressure is $80/50$ mm Hg, heart rate is $122$ /min, and respiratory rate is $28$ /min. Abdominal examination reveals severe distension, diffuse tenderness, and involuntary guarding. Laboratory results are as follows:

Laboratory Test	Result
Sodium	$132$ mEq/L
Potassium	$3.1$ mEq/L
Chloride	$82$ mEq/L
Bicarbonate	$16$ mEq/L
Blood urea nitrogen	$45$ mg/dL
Creatinine	$2.2$ mg/dL
Lactate	$7.5$ mmol/L

Arterial blood gas (room air):

Parameter	Result
pH	$7.50$
pCO $_2$	$21$ mm Hg
pO $_2$	$68$ mm Hg

Based on the clinical presentation and laboratory results, which of the following sets of acid-base disorders is present in this patient?

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

High anion gap metabolic acidosis and respiratory alkalosis

High anion gap metabolic acidosis, normal anion gap metabolic acidosis, and respiratory alkalosis

High anion gap metabolic acidosis and metabolic alkalosis

Normal anion gap metabolic acidosis, metabolic alkalosis, and respiratory alkalosis

Show answer & explanation

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

Answer

The correct answer is the set containing a high anion gap metabolic acidosis, a metabolic alkalosis, and a respiratory alkalosis.

The patient's ABG shows an alkalemia (pH >

7.45

) driven by hypocapnia (pCO

_2

<

40

mm Hg), indicating a primary respiratory alkalosis. This is clinically consistent with hyperventilation due to severe sepsis and fever. Next, calculating the anion gap (AG): AG = Na

^+

- (Cl

^-

+ HCO

_3^-

) =

132 - (82 + 16) = 34

mEq/L. Since the normal AG is

12

mEq/L, an AG of

34

confirms the presence of a high anion gap metabolic acidosis (HAGMA), resulting from lactic acidosis due to septic shock. Finally, to check for a third disorder, a delta-delta calculation is performed. The

\Delta

AG is

34 - 12 = 22

. The corrected HCO

_3^-

= measured HCO

_3^-

+

\Delta

AG =

16 + 22 = 38

mEq/L. Because the corrected HCO

_3^-

(

38

mEq/L) is significantly greater than the normal baseline (

24

mEq/L), there is a concurrent metabolic alkalosis. This is clinically explained by the patient's ongoing use of high-dose loop diuretics for his cirrhosis. Therefore, a triple acid-base disorder is present.

Step-by-Step Solution

1

Analyze the pH to determine the primary acid-base disturbance.

The pH is

7.50

, indicating alkalemia.

Establishing the primary disturbance helps anchor the subsequent interpretation.

2

Evaluate the pCO

_2

and HCO

_3^-

to identify the driver of the alkalemia.

The pCO

_2

is markedly low at

21

mm Hg, and the HCO

_3^-

is low at

16

mEq/L. The low pCO

_2

explains the alkalemia, confirming a primary respiratory alkalosis.

Respiratory alkalosis in this patient is driven by hyperventilation secondary to sepsis and fever.

3

Calculate the anion gap (AG) to check for a metabolic acidosis.

AG = Na

^+

- (Cl

^-

+ HCO

_3^-

) =

132 - (82 + 16) = 34

mEq/L.

An AG >

12

mEq/L indicates a high anion gap metabolic acidosis (HAGMA), driven here by lactic acidosis from septic shock.

4

Perform a delta-delta calculation to unmask any hidden third disorder.

\Delta

AG =

34 - 12 = 22

. Corrected HCO

_3^-

= measured HCO

_3^-

(

16

) +

\Delta

AG (

22

) =

38

mEq/L.

Because the corrected HCO

_3^-

(

38

mEq/L) is significantly greater than the baseline of

24

mEq/L, there is a concurrent metabolic alkalosis, likely secondary to loop diuretic therapy.

Key Concept

Diagnosis of triple acid-base disorders using the anion gap and delta-delta calculations.

Alternative Method

Instead of using the corrected bicarbonate formula, the delta ratio (

\Delta

AG /

\Delta

HCO

_3^-

) can be used.

\Delta

AG =

34 - 12 = 22

.

\Delta

HCO

_3^-

=

24 - 16 = 8

. The delta ratio is

22 / 8 = 2.75

. A delta ratio greater than

2.0

confirms the presence of a concurrent metabolic alkalosis.

Estimated Time:2m 0s

Question 778Question →

Match each characteristic physical examination or radiographic hand finding to the most likely underlying rheumatologic or musculoskeletal condition.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The correct matches correlate specific patterns of joint involvement and radiographic destruction to their classic etiologies: SLE (Jaccoud arthropathy), Psoriatic arthritis (pencil-in-cup, dactylitis), Hemochromatosis (2nd/3rd MCP hook-like osteophytes), Gout (rat-bite erosions), and Osteoarthritis (1st CMC squaring, Heberden nodes).

Each condition presents with a highly specific anatomical and radiographic pattern. SLE features ligamentous laxity without bone erosion (Jaccoud arthropathy). Psoriatic arthritis combines inflammation of the entire digit (dactylitis) with aggressive osteolysis (pencil-in-cup). Hemochromatosis uniquely targets the 2nd and 3rd MCP joints. Chronic gout produces asymmetric, overhanging erosions from tophi. Osteoarthritis targets the DIP and 1st CMC joints with osteophyte formation rather than inflammatory erosions.

Step-by-Step Solution

1

Analyze the description of non-erosive, reducible hand deformities.

Matches with Systemic lupus erythematosus.

Reducible deformities without bone destruction are the hallmark of Jaccoud arthropathy, typical of SLE.

2

Identify the etiology of diffuse digit swelling with 'pencil-in-cup' destructive changes.

Matches with Psoriatic arthritis.

Dactylitis and aggressive focal osteolysis at the interphalangeal joints point directly to psoriatic arthritis.

3

Evaluate atypical metacarpophalangeal involvement featuring hook-like osteophytes.

Matches with Hemochromatosis-associated arthropathy.

The 2nd and 3rd MCP joints are classically affected in hemochromatosis, distinctly differentiating it from primary osteoarthritis.

4

Associate periarticular erosions featuring overhanging edges with a specific crystal arthropathy.

Matches with Chronic tophaceous gout.

Tophi cause mechanical displacement and erosions of adjacent bone, producing the classic 'rat-bite' radiographic appearance.

5

Recognize classic degenerative changes involving the thumb base and distal fingers.

Matches with Osteoarthritis.

Squaring of the 1st CMC joint and bony hypertrophy of the DIP joints (Heberden nodes) are the most common presentations of primary osteoarthritis.

Key Concept

Distinctive radiographic and clinical hand findings reliably differentiate among various crystal-induced, autoimmune, and degenerative arthropathies.

Estimated Time:2m 0s

Question 779Question →

A 54-year-old man with a history of severe alcohol use disorder is admitted to the intensive care unit with acute necrotizing pancreatitis. Over the past 72 hours, he has experienced intractable vomiting and an inability to tolerate any oral intake. On physical examination, the patient is lethargic. Mucous membranes are extremely dry, and skin turgor is poor. Vital signs show a blood pressure of 88/50 mmHg, a pulse of 118/min, and a respiratory rate of 22/min.

Laboratory studies reveal the following:

Variable	Value
Sodium ( $Na^+$ )	138 mEq/L
Potassium ( $K^+$ )	3.1 mEq/L
Chloride ( $Cl^-$ )	92 mEq/L
Bicarbonate ( $HCO_3^-$ )	16 mEq/L
Blood urea nitrogen (BUN)	45 mg/dL
Creatinine	2.1 mg/dL
Albumin	1.6 g/dL
Lactic acid	6.2 mmol/L

The physician evaluates the patient's acid-base status. Assuming a baseline normal anion gap of 12 mEq/L and a normal serum bicarbonate of 24 mEq/L, what is the patient's calculated delta ratio ( $\Delta\text{AG}/\Delta\text{HCO}_3^-$ ) after appropriately correcting the anion gap for his hypoalbuminemia?

Show answer & explanation

Answer: 3

Answer

3.0

This patient has an elevated anion gap metabolic acidosis secondary to profound lactic acidosis (from tissue hypoperfusion) and likely starvation ketoacidosis. Concurrently, his intractable vomiting introduces a primary metabolic alkalosis. To accurately quantify this mixed disorder, the delta ratio must be calculated. First, the measured anion gap is calculated as

138 - (92 + 16) = 30

mEq/L. Because albumin is a major circulating unmeasured anion, severe hypoalbuminemia (1.6 g/dL) falsely lowers the measured anion gap. The corrected anion gap is

30 + 2.5 \times (4.0 - 1.6) = 36

mEq/L. The

\Delta\text{AG}

is

36 - 12 = 24

mEq/L. The change in bicarbonate (

\Delta\text{HCO}_3^-

) is

24 - 16 = 8

mEq/L. The delta ratio is

24 / 8 = 3.0

. A delta ratio greater than 2.0 indicates that the bicarbonate is higher than expected, confirming a concurrent metabolic alkalosis (from vomiting).

Step-by-Step Solution

1

Calculate the measured anion gap (AG).

138 - (92 + 16) = 30 mEq/L.

The standard anion gap is necessary to identify the presence of unmeasured anions (e.g., lactate).

2

Correct the anion gap for hypoalbuminemia.

30 + 2.5 \times (4.0 - 1.6) = 30 + 2.5 \times 2.4 = 30 + 6.0 = 36 mEq/L.

Albumin is a major unmeasured weak acid. In severe hypoalbuminemia, the measured anion gap is falsely lowered and must be corrected to reveal the true extent of the metabolic acidosis.

3

Calculate the change in anion gap (

\Delta\text{AG}

).

36 - 12 = 24 mEq/L.

This value represents the excess unmeasured anions above the baseline normal value of 12 mEq/L.

4

Calculate the change in bicarbonate (

\Delta\text{HCO}_3^-

).

24 - 16 = 8 mEq/L.

This determines how much the serum bicarbonate has fallen from the normal baseline of 24 mEq/L due to buffering.

5

Calculate the delta ratio.

24 / 8 = 3.0.

The delta ratio compares the rise in unmeasured anions to the fall in bicarbonate, helping to identify mixed acid-base disorders.

Key Concept

In patients with high anion gap metabolic acidosis, the measured anion gap must be corrected for hypoalbuminemia before calculating the delta ratio to accurately identify mixed acid-base disorders.

Question 780Question →

A $45$ -year-old woman is brought to the emergency department by her husband due to a severe, throbbing headache, blurred vision, and worsening shortness of breath over the past $48$ hours. She was diagnosed with diffuse cutaneous systemic sclerosis $3$ years ago. Her home medications include mycophenolate mofetil. She recently visited an urgent care clinic for dysuria, and a urine culture sent at that time grew $>100,000$ CFU/mL of *Escherichia coli* susceptible to amoxicillin, nitrofurantoin, and ceftriaxone. She has not yet started antibiotic therapy.

Today, her temperature is $37.1^\circ C$ ( $98.8^\circ F$ ), blood pressure is $225/125$ mmHg, pulse is $110$ /min, and respirations are $26$ /min. Oxygen saturation is $93\%$ on room air. Physical examination reveals taut, thickened skin over the face, chest, and upper extremities. Funduscopic examination demonstrates bilateral papilledema and flame-shaped hemorrhages. Lung auscultation reveals fine bibasilar crackles.

Laboratory results are as follows:

Test	Result	Reference Range
Hemoglobin	$8.9$ g/dL	$12.0-16.0$ g/dL
Platelets	$85,000$ /mm³	$150,000-400,000$ /mm³
Serum creatinine	$3.4$ mg/dL (baseline $0.8$ )	$0.6-1.1$ mg/dL
Thyroid-stimulating hormone (TSH)	$2.2$ $\mu$ U/mL	$0.5-5.0$ $\mu$ U/mL
Free T4	$0.7$ ng/dL	$0.9-1.7$ ng/dL

Arterial blood gas on room air:
pH: $7.32$
pCO₂: $30$ mmHg
pO₂: $72$ mmHg
HCO₃⁻: $15$ mEq/L

Peripheral blood smear shows numerous schistocytes.

Which of the following is the most appropriate initial step in the management of this patient's condition?

Initiate therapy with an angiotensin-converting enzyme inhibitor

Administer intravenous piperacillin-tazobactam

Administer intravenous sodium bicarbonate

Administer nebulized albuterol and intravenous furosemide

Administer intravenous levothyroxine

Show answer & explanation

Answer: Initiate therapy with an angiotensin-converting enzyme inhibitor

Answer

Initiate therapy with an angiotensin-converting enzyme inhibitor

The correct intervention is to initiate an angiotensin-converting enzyme (ACE) inhibitor. This patient is experiencing scleroderma renal crisis (SRC), a medical emergency classically seen in diffuse cutaneous systemic sclerosis. It is characterized by the sudden onset of malignant hypertension, acute kidney injury, and frequently microangiopathic hemolytic anemia (indicated by schistocytes and thrombocytopenia). The pathophysiology involves severe proliferation of the renal arcuate and interlobular arteries, leading to renal ischemia and massive activation of the renin-angiotensin-aldosterone system (RAAS). ACE inhibitors (such as short-acting oral captopril) are uniquely life-saving in SRC. Crucially, even though ACE inhibitors can typically worsen acute kidney injury, SRC is the major exception where they must be aggressively up-titrated to control blood pressure and reverse the primary disease process.

Step-by-Step Solution

1

Identify the primary clinical syndrome from the patient's history and vital signs.

A patient with diffuse cutaneous systemic sclerosis presents with malignant hypertension (225/125 mmHg), encephalopathy (headache, blurred vision, papilledema), and acute kidney injury (creatinine 3.4 mg/dL).

Recognizing the triad of systemic sclerosis, severe hypertension, and acute renal failure points directly to scleroderma renal crisis (SRC).

2

Evaluate the laboratory findings to confirm the diagnosis and rule out complications.

Labs show microangiopathic hemolytic anemia (schistocytes, thrombocytopenia, low hemoglobin) which frequently accompanies SRC due to endothelial injury. Acid-base status shows a fully compensated metabolic acidosis. Thyroid labs reflect euthyroid sick syndrome.

Confirming MAHA supports the severity of the vascular injury in SRC. The other laboratory abnormalities are secondary to the acute illness and AKI.

3

Determine the most critical pharmacologic intervention for this specific rheumatologic emergency.

Angiotensin-converting enzyme (ACE) inhibitors are the only therapy proven to reverse the profound renin-angiotensin-aldosterone system activation in SRC.

Unlike most other causes of AKI where ACE inhibitors are discontinued, SRC uniquely requires the prompt initiation and rapid titration of short-acting ACE inhibitors (like captopril) to prevent permanent renal failure and death.

Key Concept

Scleroderma renal crisis (SRC) presents with malignant hypertension, acute kidney injury, and microangiopathic hemolytic anemia in a patient with systemic sclerosis. The cornerstone of management is the immediate initiation of an ACE inhibitor.

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