Predictors of relapse of polymyositis/dermatomyositis associated interstitial lung disease

Background: Polymyositis/dermatomyositis (PM/DM) patients often develop interstitial lung disease (ILD), which can lead to relapse despite anti-inflammatory treatments. This study aims to elucidate the clinical characteristics of relapses in PM/DM-associated ILD patients. Methods: We gathered clinical data, including laboratory results, pulmonary function tests, chest high-resolution computed tomography findings from patients treated at Okinawa Chubu Hospital between January 1, 2010 and December 31, 2018. Results: We identified a total of 74 patients, comprising 21 men and 53 women. Among them, 38 patients remained relapse-free with maintenance therapy, while 36 experienced relapses despite immunosuppressive management. We followed these patients until June 30, 2023, and 13 patients died. The median survival period was 51.4 months (range, 0.3–214 months). When comparing clinical variables, relapsed patients tended to be younger (49.9 vs. 64.1 years), reported myalgia and rash more frequently (63.9% vs. 28.9% and 61.15% vs. 21.1%, respectively). In terms of laboratory findings, lactate dehydrogenase (LDH) levels were higher in relapsed patients (613±464 vs. 381±203 U/L). Radiological findings showed that ground glass opacity (GGO) was more prevalent in relapsed patients (58.3% vs. 16.7%). A Cox-proportional hazards model for relapse demonstrated that serum LDH [hazard ratio (HR) 1.005, 95% confidence interval (CI): 1.000–1.009, P=0.02] and GGO (HR 1.863, 95% CI: 1.103–3.147, P=0.02) were valuable predictors of relapse. Receiver operating characteristic curve analysis of serum LDH indicated that a threshold of 450 correctly classified relapse in PM/DM-associated ILD patients. Conclusions: Serum LDH and GGO may serve as predictors of relapse in PM/DM-associated ILD patients.