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Difficulty: MediumRheumatology and Immunology

A 48-year-old male with a 20-pack-year smoking history is admitted to the hospital with a three-week history of worsening cough, blood-tinged sputum, and profound fatigue. Over the last six months, he has experienced chronic nasal crusting, recurrent epistaxis, and sinus pressure that failed to improve with over-the-counter decongestants. His temperature is 37.9°C (100.2°F), blood pressure is 158/92 mmHg, and pulse is 98/min. Physical examination reveals a mild saddle nose deformity and bilateral lung crackles. Recent outpatient laboratory testing showed a normal thyroid-stimulating hormone (TSH) level of 2.1 µU/mL and a low free thyroxine (T4) level. Current admission laboratory results are as follows:

TestResult
Blood urea nitrogen42 mg/dL
Serum creatinine2.6 mg/dL (baseline 0.9 mg/dL)
Serum bicarbonate16 mEq/L
Arterial pCO235 mmHg

Urinalysis demonstrates 3+ blood, 2+ protein, and numerous dysmorphic red blood cells. A chest radiograph reveals multiple bilateral nodular opacities, several of which have central cavitation. A rapid sputum gram stain from the emergency department is negative for organisms. Which of the following is the most appropriate next step in the patient's care?

  1. Measurement of serum antineutrophil cytoplasmic antibodiesAnswer
  2. B
    Initiation of empiric broad-spectrum antimicrobial therapy
  3. C
    Administration of intravenous furosemide for acute decompensated heart failure
  4. D
    Initiation of levothyroxine therapy for primary hypothyroidism
  5. E
    Administration of intravenous sodium bicarbonate to correct uncompensated metabolic acidosis

Answer

Measurement of serum antineutrophil cytoplasmic antibodies
The patient's presentation is highly characteristic of Granulomatosis with Polyangiitis (GPA, formerly Wegener's granulomatosis). GPA is a small-vessel systemic vasculitis classically presenting with a triad of upper respiratory tract manifestations (recurrent epistaxis, nasal septal perforation resulting in a saddle nose deformity), lower respiratory tract manifestations (hemoptysis, bilateral cavitary lung nodules), and renal manifestations (rapidly progressive glomerulonephritis presenting with acute kidney injury, proteinuria, and dysmorphic red blood cells). The most appropriate next step in the evaluation of a patient with suspected GPA is the measurement of serum antineutrophil cytoplasmic antibodies (ANCA). Approximately 90% of patients with active, generalized GPA will have a positive c-ANCA (directed against proteinase-3, PR3). While a tissue biopsy (often of the lung or kidney) is ultimately required for definitive diagnosis, ANCA testing is the standard initial serologic workup.

Step-by-Step Solution

1
Analyze the clinical triad presented in the vignette.
The patient has upper respiratory involvement (nasal crusting, saddle nose), lower respiratory involvement (cavitary lung nodules, hemoptysis), and renal involvement (rapidly progressive glomerulonephritis).
Identifying this specific triad of organ systems is crucial for recognizing Granulomatosis with Polyangiitis (GPA).
2
Rule out alternative etiologies based on laboratory and imaging data.
Infection is less likely given the negative gram stain and chronicity of upper airway symptoms. Heart failure is ruled out by the cavitary nature of the nodules and dysmorphic RBCs in the urine.
Differentiating systemic vasculitis from infectious or cardiopulmonary etiologies prevents inappropriate therapies.
3
Determine the optimal next step for the suspected autoimmune disease.
Testing for antineutrophil cytoplasmic antibodies (specifically c-ANCA/PR3-ANCA) is the most appropriate initial non-invasive diagnostic test to support the diagnosis of GPA before proceeding to tissue biopsy.
Serologic confirmation guides subsequent aggressive immunosuppressive therapy.

Key Concept

Diagnosis of Granulomatosis with Polyangiitis (GPA)
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Topics

Rheumatology and Immunology

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