Objective: To test the hypothesis that preexisting lung disease is a risk factor for the development of methotrexate (MTX) pneumonitis in patients with rheumatoid arthritis (RA) treated with low dose MTX.
Methods: We measured the proportion of patients with and without preexisting lung disease who developed MTX pneumonitis in a historical cohort from a university affiliated rheumatology private practice in Chicago. Patients comprised 93 women and 32 men with RA treated with MTX for any period of time between January, 1980 and July, 1989.
Results: MTX pneumonitis occurred in 4 of 77 patients without preexisting lung disease (5.2%) and 5 of 29 (17.2%) patients with preexisting lung disease (p = 0.0610, Fisher's exact test). Five of 24 (20.1%) patients with preexisting lung disease characterized by the report of an abnormal chest radiograph developed MTX pneumonitis (p = 0.2328, Fisher's exact test) and 4 of 16 (25%) patients with interstitial infiltrates reported on their chest radiograph developed MTX pneumonitis (p = 0.0276, Fisher's exact test).
Conclusion: The presence of preexisting lung disease characterized by radiographic interstitial infiltrates predisposes patients with RA to develop MTX pneumonitis.