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Methotrexate pneumonitis — SCE Rheumatology MCQ

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EasyRheumatological pharmacologyMethotrexate pneumonitisSCE Rheumatology

A 62-year-old woman with rheumatoid arthritis started methotrexate 4 months ago. She develops a 10-day history of progressive breathlessness, dry cough and fever. Examination reveals fine bibasal crackles. HRCT demonstrates diffuse bilateral ground-glass opacification without established fibrosis, and microbiological investigations for infection are negative. What is the most likely diagnosis?

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Correct answer: E — Methotrexate pneumonitis

The diagnosis is methotrexate pneumonitis. The characteristic pattern is an acute or subacute illness with dry cough, dyspnoea, fever and inspiratory crackles in a patient taking methotrexate, accompanied by diffuse ground-glass change after infection has been excluded. RA-associated fibrotic ILD more commonly has an insidious course and established fibrotic HRCT abnormalities, often including reticulation, traction bronchiectasis or honeycombing. Community-acquired pneumonia remains an important initial differential but is less likely with diffuse interstitial change and negative microbiological investigations. Pulmonary embolism does not usually cause this febrile interstitial syndrome, while heart failure would be supported by congestion, oedema or cardiac findings rather than isolated diffuse inflammatory ground-glass change.

Reference: Electronic Medicines Compendium. Methotrexate 2.5 mg Tablets, Summary of Product Characteristics, sections 4.4 and 4.8; updated 20 January 2025. https://www.medicines.org.uk/emc/product/511/smpc