Interstitial lung disease in polymyositis and dermatomyositis: longitudinal evaluation by pulmonary function and radiology.

OBJECTIVE: To estimate predictors and long-term outcome of interstitial lung disease (ILD) in patients with polymyositis (PM) and dermatomyositis (DM).
METHODS: We conducted a prospective study in which newly diagnosed PM/DM patients, regardless of clinical symptoms of pulmonary disease, were investigated with repeated chest radiography, high-resolution computed tomography (HRCT) of the lungs, and pulmonary function test (PFT). Clinical, radiologic, and lung function outcome was based on the last followup results.
RESULTS: Twenty-three patients with a mean followup period of 35 months were included. Findings on radiographic examination and/or PFT compatible with ILD were recorded in 18 patients (78%). Patients with ILD had lower lung function, higher radiologic scores, and higher creatine kinase values than those without ILD. All patients were treated with high-dose glucocorticoids and other immunosuppressive agents. Two patients died due to ILD, both with active myositis. During the followup, total lung capacity (TLC) improved in 33%, remained stable in 39%, and deteriorated in 28%. Changes in TLC correlated only partially with HRCT findings, which persisted even after normalizing for lung function.
CONCLUSION: ILD associated with PM/DM is in most cases mild, chronic, and has a nonprogressive course during immunosuppressive treatment. PFT can be normalized during treatment with immunosuppressive therapy, even if radiologic signs of ILD persist. The course of ILD could not be predicted on the first examination. Therefore, myositis patients with ILD need careful evaluation of clinical features as well as PFT and radiologic features during followup.