Methotrexate pneumonia lacking dyspnea and radiographic interstitial patterns during treatment for early rheumatoid arthritis: bronchoalveolar lavage and transbronchial lung biopsy in a differential diagnosis.

Methotrexate (MTX) pneumonia is an unpredictable and sometimes life-threatening adverse effect occurring in the treatment of rheumatoid arthritis (RA). We present a case of MTX pneumonia lacking severe respiratory symptoms and typical radiographic findings. A 66-year-old man with early RA presented with intermittent fever and nonproductive cough during the MTX therapy, but neither hypoxemia nor dyspnea was a complaint. His chest X-ray films revealed multiple bilateral consolidations, but interstitial infiltrates were not observed. High-resolution computed tomography showed no ground-glass opacities. In contrast, the histological findings of transbronchial lung biopsy (TBLB) samples were characterized by the interstitial infiltration of mononuclear cells and hyperplasia of type II alveolar cells, which are the main features of drug-induced interstitial inflammation. Special stains for microorganisms were negative for the TBLB samples. Although cultures of bronchoalveolar lavage (BAL) fluids were slightly positive for Haemophilus influenzae, intensive antibiotic therapy was ineffective. A discontinuation of MTX followed by steroid therapy induced the patient's dramatic recovery. A new treatment with tacrolimus was started for RA. We would like to emphasize that the histological examinations and microbiological studies using BAL and TBLB are useful for the exclusion of other causes and the diagnosis of MTX pneumonia, especially in a case without typical respiratory symptoms and radiographic patterns.