Methotrexate-induced pneumonitis is a rare but potentially fatal side effect. It is a diagnosis of exclusion. There are early and late forms and different cell patterns in the bronchoalveolar lavage (BAL).
We present a case of acute interstitial lung disease in a 54-year-old patient who had been taking methotrexate for a year and a half for rheumatoid arthritis. After excluding other causes and based on the diagnostic criteria of Searles and McKendry, we could reasonably identify methotrexate as the cause of the lung disease. It was of late onset and the BAL showed neutrophilia and eosinophilia.
Methotrexate-induced pneumonitis is a diagnosis of exclusion. A late onset combined with the predominance of neutrophils and eosinophils in BAL is rare in the literature, demonstrating the wide heterogeneity of methotrexate-related interstitial lung disease.