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MTX Pneumonitis vs RA-ILD — SCE Rheumatology MCQ

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ModerateRheumatoid ArthritisMTX Pneumonitis vs RA-ILDSCE Rheumatology

A 50-year-old woman with seropositive rheumatoid arthritis started methotrexate 10 weeks ago. Over the past 3 weeks, she has developed a dry cough, fever and progressive exertional breathlessness. Her oxygen saturation is 91% on air and fine bibasal crackles are present. High-resolution CT shows new bilateral diffuse ground-glass and interstitial opacities; previous chest imaging was normal. Initial microbiological investigations and cardiac assessment have not identified infection or pulmonary oedema. Which pair of diagnoses should now be prioritised?

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Correct answer: A — Methotrexate pneumonitis and rheumatoid arthritis-associated interstitial lung disease

The correct answer is **A**. Methotrexate pneumonitis and RA-associated interstitial lung disease can both cause dry cough, breathlessness, hypoxaemia and bilateral interstitial or ground-glass abnormalities. The acute–subacute febrile illness shortly after starting methotrexate, with previously normal imaging, particularly raises concern for methotrexate pneumonitis; RA-ILD more commonly follows an insidious course, although acute presentations can occur. Methotrexate should be withheld while infection, including opportunistic infection, is rigorously excluded. Bronchoalveolar lavage may help exclude infection but no BAL differential count, including eosinophilia, is diagnostic. Pulmonary embolism, COPD and asthma do not adequately explain diffuse interstitial opacities. Sarcoidosis, malignancy and alveolar haemorrhage are less consistent with the clinical tempo and absence of their characteristic associated findings.

Reference: Methotrexate 2.5 mg Tablets, Summary of Product Characteristics, section 4.4 Respiratory effects, updated 20 January 2025. https://www.medicines.org.uk/emc/product/511/smpc