OBJECTIVES To identify factors associated with deterioration of pulmonary function with disproportional decline in diffusing capacity for carbon monoxide (DLCO) relative to forced vital capacity (FVC) in patients with dermatomyositis (DM) and polymyositis (PM).

METHODS This retrospective cohort study included patients with DM and PM, in whom serial pulmonary function tests were available. Changes in FVC and DLCO over time were estimated using a linear mixed-effects model.

RESULTS A total of 103 patients were included. During follow-up, 31 (30.1%) and 37 (35.9%) had a disproportionally better (ΔDLCO/ΔFVC>mean slope + 95% CI) or a disproportionally worse (ΔDLCO/ΔFVC <mean slope - 95% CI) DLCO change relative to FVC change. After adjusting for age, gender and diagnosis, Raynaud's phenomenon (RP) and anti-nuclear antibodies (ANA) increased the risk of disproportional DLCO decline (odds ratio [OR]: 6.32, 95% CI: 1.34-29.81, P = 0.022; OR: 3.92, 95% CI: 1.21-12.67, P = 0.020, respectively). Patients with ANA and RP tended to deteriorate, whereas those without ANA and RP improved (FVC: -4.5 ± 14.4 vs 11.1% ± 27.5%/y, P = 0.38; DLCO: -17.0 ± 24.9 vs 9.8% ± 25.4%/year, P = 0.015). More patients with ANA and RP tended to reach progressive DLCO decline (DLCO <40%) than ANA/RP-negative patients (P = 0.05). Trends toward higher rates of pulmonary hypertension and higher systolic pulmonary arterial pressure were observed in those with both ANA and RP.

CONCLUSION This study identifies RP and ANA as risk factors for the deterioration of pulmonary function with disproportional DLCO decline relative to FVC.