Methotrexate-induced pneumonitis in patients with rheumatoid arthritis and psoriatic arthritis: report of five cases and review of the literature.

Pneumonitis is emerging as one of the most unpredictable and potentially serious, adverse effects of treatment with MTX. Its prevalence in rheumatoid arthritis (RA) has been estimated from several retrospective and prospective studies to range from 0.3% to 18%. On the other hand, MTX-induced pneumonitis seems to be very rare in psoriatic arthritis (PsA). Our review of 194 RA patients and 38 PsA patients receiving MTX has identified four RA patients and one PsA patient with MTX-induced pneumonitis, giving a prevalence of 2.1% and 0.03%, respectively. Diagnosis was suggested by clinical history and radiographic findings, but the bronchoalveolar lavage plays an important role both in excluding infectious agents and in providing information for understanding the pathogenesis of lung injury. The presence of a lymphocyte alveolitis with a predominance of CD4+ T cells in 3 RA patients and CD8+ T cells with a concomitant increase in neutrophils in another case suggests that immunologically mediated reactions may be one damage mechanism in MTX-induced pneumonitis. Although risk factors for MTX-induced pulmonary toxicity are poorly understood, the presence in 3 out of 5 of our patients of pre-existing lung disease, represented by diffuse interstitial changes on chest X-ray, and mild bronchial asthma in two RA patients and by pulmonary silicosis in the patient with PsA may account for a predisposition to the development of MTX pneumonitis.