Prevalence and Clinical Correlates of Myositis Specific Autoantibodies in Idiopathic Immune-Mediated Inflammatory Myositis - Results from a Multicentric Cohort (MyoIN) from India.

There is a need to understand the clinical and antibody associations in patients with IIM in various ethnicities and geographical areas. Patients who fulfilled Bohan's and Peter criteria of IIM and seen between October 2017 through Jan 2020 were enrolled in this study at 3 centres. Clinical and relevant laboratory parameters were recorded in a pre designed case record form. MSA and MAA to 16 antigens were performed by line blot assay using Euroimmun (Luebec, Germany) as per manufacturer's instruction. Of the 150 patients, 13 were juvenile onset. Ninety sera had either one MSA or MAA. Sixty sera had neither MSA/MAA. anti-Ro 52 were the commonest antibody and anti-Mi-2α and b the commonest MSA. Novel associations identified were severe myositis with anti-Ro 52, cutaneous ulcerations with anti-MDA5 and anti-PM-Scl and calcinosis with anti-PM-Scl. One-third sera had no MSA or MAA. Larger sample size and use of antibody assays together with muscle biopsy will improve subtyping and phenotype associations in IIM.