According to the results of a study published in Rheumatology, independent predictors of short-term dermatomyositis (DM)- or polymyositis (PM)-related interstitial lung disease (ILD) mortality include age at disease onset, C-reactive protein level (CRP), peripheral capillary oxygen saturation (SpO2), and anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5).
Investigators established the Multicentre Retrospective Cohort of Japanese Patients with Myositis-associated ILD, which included 497 participants with PM/DM-associated ILD from 44 centers across Japan. The inclusion criteria were an age of disease onset ≥16 years, definite or probable PM/DM or clinically amyopathic DM, the presence of ILD as determined by the American Thoracic Society criteria and a multidisciplinary assessment of clinical, radiologic, and pathologic findings, and availability of serum samples at diagnosis for comprehensive myositis-specific autoantibody analysis.
The study cohort consisted mostly of classic DM and clinically amyopathic DM; only 15% of cases were identified as PM. Univariate and multivariate analyses were conducted to identify predictive factors of mortality resulting from respiratory insufficiency directly related to PM/DM-associated ILD.
The median period of observation was 20 months. During this period, 93 patients died, 82% of whom had a cause of death related to respiratory deficiency resulting from ILD. Results from a multivariate analysis identified 4 independent risk factors for ILD mortality, including age at onset ≥60 years (hazard ratio [HR], 4.3; 95% CI, 2.4-7.5; P <.001), CRP ≥1 mg/dL (HR, 2.6; 95% CI, 1.5-4.8; P =.001), SpO2 <95% (HR, 2.0; 95% CI, 1.2-3.4; P =.011), and anti-MDA5 (HR, 7.5; 95% CI, 2.8-20.2; P <.001). Even after the inclusion of drugs used for induction treatment as possible confounders, the 4 factors remained statistically significant.
The most significant predictor was the anti-MDA5 antibody, with a 7.5-fold increase in risk (P <.001). Results showed that 88% of deaths occurred in patients with the anti-MDA5 antibody.
“Since age, CRP and SpO2 are readily available in routine clinical practice, and kits to measure the anti-MDA5 antibody are now commercially available, our findings are widely applicable for identifying PM/DM patients with intractable ILD who require intensive treatment at an early stage,” the authors added. “Our results will also assist in designing appropriate patient inclusion criteria for future clinical trials for PM/DM-associated ILD.”
Sato S, Masui K, Nishina N, et al. Initial predictors of poor survival in myositis-associated interstitial lung disease: a multicentre cohort of 497 patients [published online March 27, 2018]. Rheumatology. doi:10.1093/rheumatology/key060