Myositis-specific autoantibodies and their clinical associations in Idiopathic Inflammatory Myopathies
Abstract Background The aims of the study were to investigate the prevalence of myositis specific autoantibodies (MSAs) and their associated complications in a cohort of patients with idiopathic inflammatory myopathies (IIMs). Methods A total of 201 consecutive patients with IIMs being followed up in the Rheumatology clinics of the participating regional hospitals in Hong Kong from July 2016 to January 2018 were recruited. Clinical characteristics, treatment history and disease complications were documented. Immunoblot assay was used to detect the MSAs.Results Out of the 201 patients, at least one MSA was found in 63.2% of patients. The most common MSAs were the anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5 Ab) and the anti-transcriptional intermediary factor 1-gamma antibody (anti-TIF1-γ Ab) (both 13.9%), followed by anti-Jo-1 antibody (12.4%). Anti-MDA5 Ab was present exclusively in dermatomyositis (DM) and was strongly associated with digital ulcers, the clinically amyopathic phenotype and rapidly progressive interstitial lung disease (RP-ILD). Anti-TIF1γ Ab was strongly associated with refractory rash and malignancy. Multivariate analysis showed that the independent risk factors of RP-ILD included anti-MDA5 Ab (OR 14.5, p=0.001), clinically amyopathic DM (OR 13.9, p=0.015) and history of pulmonary tuberculosis (OR 12.2, p=0.026). Cox regression analysis showed that the independent predictors of malignancy included anti-TIF1γ Ab (HR 3.55, p=0.002), DM (HR 3.82, p=0.009) and family history of cancer (HR 3.40, p=0.038). Conclusions MSA testing enables dividing of patients with IIMs into phenotypically homogenous subgroups and prediction of potentially life-threatening complications.