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Antimelanoma Differentiation-associated Gene 5 Antibody: Expanding the Clinical Spectrum in North American Patients with Dermatomyositis

Objective. To determine the clinical features associated with the antimelanoma differentiation-associated gene 5 antibody (anti-MDA5) in US patients with clinically amyopathic dermatomyositis (CADM) and classic DM. Methods. Patients with CADM were consecutively selected from the University of Pittsburgh Myositis Database from 1985 to 2013. CADM was defined by a typical DM rash without objective muscle weakness and no or minimal abnormalities of muscle enzymes, electromyography, or muscle biopsy. DM was defined by Bohan and Peter criteria and was 1:1 matched (sex and age ± 5 yrs) to patients with CADM. Anti-MDA5 autoAb levels were determined using ELISA. Clinical features were compared between CADM and DM and between MDA5-positive and MDA5-negative subjects, using chi-squared and/or Mann-Whitney U tests as appropriate. Results. We identified 61 patients with CADM who were matched to 61 DM controls (female 62% vs 64%; mean age 44.8 yrs vs 48.2, p < 0.5). Anti-MDA5 frequency was the same in both cohorts (13.1%), and anti-MDA5 was significantly associated with a higher likelihood of cutaneous ulcers, digital tip ulcerations, and puffy fingers as well as interstitial lung disease (ILD). Most patients with ILD had rapidly progressive ILD (RPILD) leading to early death. Patients with CADM were more likely to have dysphagia, but there were no other clinical differences seen associated with CADM as compared to classic DM. Conclusion. Anti-MDA5 positivity had a similar frequency in US patients with CADM and DM and is associated with ILD, RPILD, cutaneous ulcers, digital tip ulceration, and poor survival.