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MTX Pneumonitis — SCE Rheumatology MCQ

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ModerateRheumatoid ArthritisMTX PneumonitisSCE Rheumatology

A 50-year-old man with rheumatoid arthritis has taken weekly methotrexate for 5 years. He develops progressive breathlessness, dry cough and fever over 10 days. Oxygen saturation is 88% on air. HRCT shows new diffuse bilateral ground-glass and interstitial opacities, and his peripheral eosinophil count is 0.9 × 10^9/L. Respiratory viral PCR, including SARS-CoV-2, and bronchoalveolar lavage testing for bacterial, fungal and Pneumocystis infection are negative. What is the most likely diagnosis?

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Correct answer: B — Methotrexate pneumonitis

The correct answer is **B, methotrexate pneumonitis**. The discriminating features are the acute/subacute onset of hypoxaemic breathlessness, dry cough and fever, diffuse bilateral interstitial opacities, peripheral eosinophilia and negative investigation for infection. Methotrexate lung toxicity can occur at any time during treatment, so 5 years of previously stable therapy does not exclude it. RA-associated ILD is usually more insidious and commonly demonstrates a fibrotic UIP or NSIP pattern rather than an acute febrile eosinophilic illness. Community-acquired and COVID-19 pneumonia are undermined by the negative microbiological assessment. Pulmonary embolism would not adequately explain the fever, eosinophilia and diffuse interstitial infiltrates. Methotrexate should be stopped immediately, infection carefully excluded and glucocorticoids considered; the drug should not subsequently be restarted.

Reference: Methotrexate 2.5 mg Tablets, Summary of Product Characteristics, sections 4.4 and 4.8, revised January 2025. https://www.medicines.org.uk/emc/product/511/smpc