A 62-year-old man comes to the clinic reporting a 3-month history of a persistent dry coug… — USMLE Step 2 CK

A $62$ -year-old man comes to the clinic reporting a $3$ -month history of a persistent dry cough and progressively worsening shortness of breath. He can currently walk only one block before needing to stop. He has a $12$ -year history of seropositive rheumatoid arthritis, which is treated with weekly oral methotrexate and daily folic acid. He is a lifelong nonsmoker. His temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $132/82\text{ mmHg}$ , pulse is $86/\text{min}$ , and respiratory rate is $20/\text{min}$ . Pulse oximetry shows $93\%$ on room air. Physical examination reveals fine, "Velcro-like" end-inspiratory crackles at both lung bases. Jugular venous pressure is normal, and cardiac examination reveals a regular rate and rhythm with no murmurs or gallops. There is no peripheral edema. Musculoskeletal examination shows ulnar deviation of the fingers bilaterally but no acute joint swelling or tenderness.

Laboratory Test	Result
Hemoglobin	$12.1\text{ g/dL}$
Leukocyte count	$6,800/\text{mm}^3$
Platelet count	$245,000/\text{mm}^3$
Brain natriuretic peptide (BNP)	$35\text{ pg/mL}$

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

High-resolution computed tomography of the chestAnswer
B
Administration of empiric levofloxacin and azithromycin
C
Initiation of intravenous furosemide therapy
D
Initiation of empiric trimethoprim-sulfamethoxazole
E
Measurement of arterial blood gas to calculate expected respiratory compensation

Answer

High-resolution computed tomography of the chest

The correct answer is high-resolution computed tomography (HRCT) of the chest. This patient's presentation of a progressive dry cough, exertional dyspnea, and fine "Velcro-like" basilar crackles in the setting of long-standing rheumatoid arthritis (RA) is highly suspicious for interstitial lung disease (ILD). ILD is a well-documented and potentially fatal extra-articular manifestation of RA (RA-ILD). Furthermore, methotrexate, a common disease-modifying antirheumatic drug (DMARD), can occasionally cause methotrexate-induced pneumonitis. Because the patient has no signs of volume overload and a normal BNP, cardiogenic pulmonary edema is effectively ruled out. The insidious timeline and normal leukocyte count make bacterial pneumonia unlikely. HRCT of the chest is the diagnostic modality of choice to evaluate suspected ILD, as it provides detailed cross-sectional imaging of the lung parenchyma, detects early fibrotic changes, and characterizes the specific radiologic pattern (such as usual interstitial pneumonia or nonspecific interstitial pneumonia).

Step-by-Step Solution

Analyze the clinical presentation and timeline.

The patient has chronic, progressive dyspnea and a dry cough over 3 months, with fine basilar crackles on exam.

Establishing the subacute to chronic timeline helps rule out acute infectious or cardiogenic events.

Integrate the past medical history and laboratory findings.

The patient has long-standing rheumatoid arthritis (RA). Heart failure is ruled out by the lack of JVD, lack of edema, and a normal BNP. Acute pneumonia is unlikely given the chronicity and lack of fever/leukocytosis.

RA is strongly associated with extra-articular manifestations, most notably Rheumatoid Arthritis-associated Interstitial Lung Disease (RA-ILD). Additionally, methotrexate can cause drug-induced pneumonitis.

Determine the optimal diagnostic test.

High-resolution computed tomography (HRCT) of the chest is selected.

HRCT is the gold standard for visualizing the lung parenchyma, confirming the presence of interstitial lung disease, and determining the specific radiologic pattern (e.g., usual interstitial pneumonia).

Key Concept

Patients with rheumatoid arthritis presenting with progressive dyspnea and crackles should be evaluated for interstitial lung disease using high-resolution computed tomography of the chest.

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