BACKGROUND: Pneumonitis is a rare but potentially life threatening side effect of methotrexate treatment for rheumatoid arthritis which needs to be distinguished from interstitial lung disease due to rheumatoid arthritis. METHODS: To examine the value of bronchoalveolar lavage (BAL) in diagnosing methotrexate pneumonitis, the BAL cell profile of four patients with methotrexate pneumonitis was compared with findings in 16 patients with rheumatoid arthritis treated with methotrexate without clinical or radiological evidence of lung disease and eight patients with interstitial lung disease secondary to rheumatoid arthritis treated with methotrexate. RESULTS: Methotrexate pneumonitis was associated with an increase in the lymphocytes in the BAL fluid to 33-68% of total BAL cells. BAL lymphocytosis was also found in five patients in each of the two control groups. The four patients with methotrexate pneumonitis had a disproportionate increase in CD4+ cells to 72-84% of total lymphocytes and in the CD4/CD8 ratio to 17.0, 6.6, 8.7, and 4.0, respectively, figures which exceeded those of the two control groups. CONCLUSIONS: Methotrexate pneumonitis was associated with lymphocytic alveolitis with a preferential increase in CD4+ cells. This pattern differs from that in interstitial lung disease due to rheumatoid arthritis and may therefore assist in making an early diagnosis of methotrexate pneumonitis.
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