Transbronchial Lung Cryobiopsy-Supported Subcutaneous Methotrexate-Induced Pneumonitis and Subsequent Rheumatoid Arthritis Organizing Pneumonias

A 61-year-old Japanese woman with a 20-year-history of rheumatoid arthritis (RA) had been treated with various antirheumatic drugs including biologics and Janus kinase inhibitors. Subcutaneous methotrexate (MTX) was added to sarilumab, resulting in improvement in her joint tenderness. Six months later, however, while continuing both agents, she developed exertional dyspnea. Computed tomography revealed bilateral ground-glass opacities, and transbronchial lung cryobiopsy (TBLC) showed pathological findings consistent with MTX-induced pneumonitis. She responded rapidly to glucocorticoids, but subsequently developed recurrent episodes of RA-associated organizing pneumonia (RA-OP) despite discontinuation of MTX, which was evaluated by repeat bronchoscopy and supported the diagnosis of RA-OP, and prolonged glucocorticoid therapy was required. MTX-induced pneumonitis is a potentially life-threatening complication. This case demonstrates that subcutaneous MTX does not eliminate the risk of pneumonitis, that TBLC is a valuable diagnostic tool allowing clear pathological characterization with ample tissue to support confident pathologic diagnosis, and that the marked discrepancy in imaging supports that repeat bronchoscopy is warranted rather than avoided when new imaging points to an alternative diagnosis.