A 62-year-old woman on long-term methotrexate for RA develops new pulmonary infiltrates and eosinophilia. Which condition is the MOST likely cause?

• A RA-related interstitial lung disease (ILD)
• B Opportunistic Pneumocystis jirovecii pneumonia
• C Drug-induced lupus from methotrexate
• D Methotrexate pneumonitis ✓

Explanation

Methotrexate pneumonitis is an idiosyncratic hypersensitivity reaction (not dose-dependent) occurring in approximately 1–3% of RA patients on methotrexate. Characteristic features include bilateral infiltrates, eosinophilia, fever, and dry cough; BAL shows eosinophilia and lymphocytosis. It can occur at any time after initiating therapy. Management requires immediate methotrexate cessation and corticosteroids. RA-ILD (UIP/NSIP patterns) lacks eosinophilia. PCP pneumonia is possible on methotrexate but presents with CD4-like features and lacks peripheral eosinophilia.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.