Study objectives: We described the features seen on serial high-resolution CT scans of nonspecific interstitial pneumonia (NSIP) that was associated with polymyositis (PM) and dermatomyositis (DM), and we correlated the changes in the CT scan findings with those of pulmonary function test results.

Design, setting and patients: Serial CT scans of 14 patients with histologically proven NSIP and PM/DM from two university hospitals were evaluated retrospectively (follow-up period, 3 to 61 months; mean follow-up period, 27.6 months). Using initial and follow-up CT scan findings, the extent of each type of opacity and the total area of increased opacity were calculated and correlated with the results of pulmonary function tests.

Measurements and results: The predominant findings on the initial CT scans were of reticular and/or ground-glass opacities with or without consolidation. Reticular and ground-glass opacities predominated in the lower zone of each lung, and consolidation predominated at the lung periphery. Thirteen patients showed significant improvement of the total area of increased opacity (p < 0.05), and this decrease in extent inversely correlated with changes in FVC (r = -0.650; p = 0.031). Ground-glass and reticular opacities also were improved significantly in 11 and 13 patients, respectively. The decrease in the extent of ground-glass opacity correlated inversely with the changes in FVC (r = -0.758; p = 0.0119) and diffusion capacity for carbon monoxide (r = -0.669; p = 0.0448). In one patient, ground-glass opacity progressed, and death occurred after 3 months. Traction bronchiectasis was seen in 12 patients, and it improved in four patients after treatment. Honeycomb lung was not noted in any patient during follow-up.

Conclusions: With treatment, serial CT scans of PM/DM patients with NSIP showed significant improvement in the abnormal opacities, and radiographic progression of lung fibrosis was limited. The CT scan features and clinical course of NSIP in PM/DM patients were relatively uniform, and this constitutes a subset of NSIP.