Methotrexate (MTX) is being used increasingly to treat rheumatoid arthritis (RA). Pneumonitis is a serious side effect of MTX therapy (P-MTX). Our aim was to determine in patients with RA the incidence and prevalence of P-MTX in Western Australia and identify risk factors for the development of this adverse reaction.
Patients with P-MTX were identified by (a) direct communication with rheumatologists in Western Australia, (b) use of a computerized clinical database, (c) questionnaire inquiry of all other rheumatologists in Australia. Possible risk factors for P-MTX were examined using age/sex matched case controls selected from the computerized clinical database.
Ten definite and 3 probable cases of P-MTX were identified. Local incidence of P-MTX was 1/35.4 patient years MTX treatment; if definite and probable cases are included (1/49.6 patient years MTX treatment for definite cases alone). Twelve patients with P-MTX were compared with 24 age/sex matched controls. A shorter duration of MTX treatment and a higher incidence of preexisting lung disease were observed in P-MTX cases but these differences were not statistically significant. No difference was observed between the P-MTX and control patients with respect to rheumatoid factor, duration of RA, use of tobacco, dose of MTX, serum creatinine, creatinine clearance or concurrent treatment with aspirin, nonsteroidal antirheumatic drugs or prednisolone.
Our results indicate that in hospital clinic patients with RA pneumonitis is a common adverse reaction. They suggest that hypersensitivity is probably responsible for most cases of pneumonitis associated with MTX, but preexisting lung disease may confer increased risk.