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Methotrexate pneumonitis — RACP Adult Medicine MCQ

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HardClinical pharmacology and toxicologyMethotrexate pneumonitisRACP Adult Medicine

A 58-year-old woman with rheumatoid arthritis taking methotrexate develops subacute dry cough, fever and dyspnoea. CT chest shows diffuse ground-glass change, cultures are negative and eosinophils are mildly elevated. Symptoms began without a dose increase. What is the most likely diagnosis?

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Correct answer: D — Methotrexate pneumonitis

Methotrexate can cause hypersensitivity pneumonitis with cough, dyspnoea, fever and diffuse interstitial changes, even without dose escalation. Lobar pneumonia would usually have focal consolidation and positive infectious features. Heart failure, amiodarone toxicity and PE do not fit the drug exposure and diffuse inflammatory pattern as well.

Reference: Australian Medicines Handbook; Therapeutic Guidelines (eTG)