A 32-year-old woman is admitted to the intensive care unit with acute-onset hemoptysis and… — USMLE Step 3

A 32-year-old woman is admitted to the intensive care unit with acute-onset hemoptysis and progressive dyspnea. Over the past three weeks, she has experienced profound fatigue, migratory arthralgias, and a diffuse maculopapular rash on her lower extremities. Her medical history is significant for Graves' disease, which was diagnosed two years ago and has been managed with propylthiouracil and propranolol.

Vital signs include a temperature of $38.1^\circ\text{C}$ ( $100.6^\circ\text{F}$ ), blood pressure of $145/92\text{ mmHg}$ , heart rate of $105/\text{min}$ , respiratory rate of $24/\text{min}$ , and oxygen saturation of $89\%$ on room air. Physical examination reveals palpable purpuric lesions on the ankles and bilateral crackles in the lung bases.

Laboratory results are as follows:

Laboratory Test	Result
Hemoglobin	$8.4\text{ g/dL}$
Platelets	$160,000/\text{mm}^3$
Leukocytes	$11,500/\text{mm}^3$
Blood urea nitrogen	$42\text{ mg/dL}$
Serum creatinine	$2.4\text{ mg/dL}$

Immunologic Study	Result
Antinuclear antibody (ANA)	Positive (1:640)
Anti-double-stranded DNA	Negative
Anti-histone antibody	Positive
p-ANCA (anti-MPO)	Positive (high titer)
c-ANCA (anti-PR3)	Positive (low titer)
Complement C3 & C4	Normal

Urinalysis shows $3+$ blood, $2+$ protein, and numerous dysmorphic red blood cells with red blood cell casts.

Which of the following is the most likely diagnosis?

A
Drug-induced lupus erythematosus
B
Microscopic polyangiitis
Drug-induced ANCA-associated vasculitisCevap
D
Systemic lupus erythematosus
E
Granulomatosis with polyangiitis

Cevap

Drug-induced ANCA-associated vasculitis

The correct diagnosis is drug-induced ANCA-associated vasculitis. This is a severe, life-threatening adverse reaction most frequently associated with the use of propylthiouracil (PTU), hydralazine, minocycline, or levamisole-adulterated cocaine. Clinically, it mimics primary small-vessel vasculitides, often presenting with pulmonary-renal syndrome (alveolar hemorrhage and rapidly progressive glomerulonephritis) and cutaneous vasculitis (palpable purpura). The key distinguishing feature that separates it from primary vasculitides (like microscopic polyangiitis) and drug-induced lupus erythematosus is its distinctive 'pan-positive' serologic profile. These patients characteristically exhibit simultaneously positive antinuclear antibodies (ANA), anti-histone antibodies, and high-titer ANCA (frequently showing dual positivity for both anti-MPO and anti-PR3). Recognizing this multi-antibody pattern in the context of an offending drug is critical for formulating the correct differential diagnosis and initiating prompt drug cessation and immunosuppression.

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Analyze the clinical presentation.

The patient has an acute pulmonary-renal syndrome characterized by alveolar hemorrhage (hemoptysis, hypoxia, crackles) and rapidly progressive glomerulonephritis (AKI, dysmorphic RBCs, RBC casts), alongside palpable purpura.

Identifying the clinical syndrome determines the initial category of disease, which in this case is a severe small-vessel vasculitis.

Evaluate the patient's medication history and serologic panel.

The patient is taking propylthiouracil (PTU). Her serology shows a 'pan-positive' profile: positive ANA, anti-histone, p-ANCA (anti-MPO), and c-ANCA (anti-PR3), with normal complement and negative anti-dsDNA.

Correlating medication exposure with precise autoantibody patterns is required to differentiate between primary autoimmune diseases and drug-induced syndromes.

Differentiate among the primary differential diagnoses.

Primary ANCA vasculitides (like microscopic polyangiitis) typically have a single positive ANCA and are ANA/anti-histone negative. Drug-induced lupus shares the ANA/anti-histone positivity but does not cause severe pulmonary-renal syndrome.

Ruling out competing diagnoses prevents premature closure and ensures the final diagnosis fully explains the clinical severity and unique lab findings.

Synthesize findings to confirm the diagnosis.

The unique combination of severe pulmonary-renal syndrome, PTU exposure, and multi-antibody positivity points definitively to drug-induced ANCA-associated vasculitis.

This condition uniquely bridges the serologic features of drug-induced lupus with the severe clinical features of ANCA-associated vasculitis.

Anahtar Kavram

Drug-induced ANCA-associated vasculitis, commonly triggered by propylthiouracil, hydralazine, or minocycline, uniquely presents with severe organ involvement (e.g., pulmonary-renal syndrome) and a characteristic 'pan-positive' autoantibody profile including ANA, anti-histone, and often dual ANCA (MPO and PR3) positivity.

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