Outcome and prognostic factors in a French cohort of patients with myositis-associated interstitial lung disease.

Interstitial lung disease (ILD) is a common form of extramuscular involvement in patients with polymyositis/dermatomyositis and is associated with poor prognosis. This study was designed to describe the long-term outcome of myositis-associated ILD. This retrospective observational study was conducted in 48 consecutive patients. Two groups defined according to outcome were compared to determine prognostic factors: a "severe" group (vital capacity [VC] < 50 % or carbon monoxide transfer factor [TLCO] < 35 % or death or lung transplantation) and a "nonsevere" group (other patients). The study population comprised 31 women and 17 men with a median age of 49.5 ± 13.6 years. Mean PFT results at the onset of ILD were 56.9 ± 23.1 % pred. for VC and 42.1 ± 16.6 % pred. for TLCO. Median (range) follow-up was 65 (2-204) months. Three patients (6.4 %) died. At last follow-up, 19 patients were classified in the "severe" group and 27 patients were classified in the "nonsevere" group. Two patients lost to follow-up after less than 12 months were excluded from this analysis. Multivariate analysis identified two independent prognostic factors: VC at onset of ILD [OR 0.95 (95 % CI 0.90-0.99)] and myopathic changes on electromyography [OR 5.76 (95 % CI 1.10-30.3)]. Patients treated in our pulmonology department for myositis-associated ILD had severe initial PFT results but a low mortality rate. Independent prognostic factors at presentation were initial VC and myopathic changes on electromyography. This study highlights the need for studies focusing on the correlation between muscle and lung pathogenic mechanisms.