A 55-year-old man with rheumatoid arthritis on methotrexate + adalimumab develops fever, cough, and bilateral ground-glass opacities on CT chest. BAL shows no pathogens. Serum beta-D-glucan is negative. The patient improved briefly after stopping adalimumab and starting broad-spectrum antibiotics, but worsened again. What is the most likely diagnosis?

• A Pneumocystis jirovecii pneumonia
• B Adalimumab-induced sarcoid reaction
• C RA-associated interstitial lung disease (UIP pattern)
• D Methotrexate-induced pneumonitis ✓

Explanation

Methotrexate pneumonitis (MTX lung) is an idiosyncratic hypersensitivity reaction occurring in 0.3–7% of RA patients on MTX, typically presenting with acute/subacute dyspnea, fever, and bilateral ground-glass opacities. Key distinguishing features: non-dose-dependent, no infection on BAL, improvement with drug cessation and corticosteroids, negative PCP workup. UIP pattern in RA is chronic and progressive. Anti-TNF agents rarely cause sarcoid-like reactions. MTX pneumonitis requires permanent drug discontinuation; reintroduction risks recurrence.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.