Myositis-specific and myositis-associated autoantibodies in Indian patients with inflammatory myositis

We aimed to study the prevalence and clinical associations of myositis-specific autoantibodies (MSAs) and myositis-associated autoantibodies (MAAs) in a large cohort of Indian patients with idiopathic inflammatory myositis (IIM). Clinical details and serum samples were collected from patients with IIM (satisfying Bohan and Peter Criteria, 1975) and CTD-associated myositis. Sera were analysed for antibodies against SRP, Mi2, Jo1, PL7, PL12, EJ, OJ, Ro52, Ku, Pm-Scl 75 and PM-Scl 100, using immunoblot assay. The cohort comprised 124 patients with IIM (M:F = 1:3.6). Fifty-five of them had dermatomyositis (DM), 22 had juvenile dermatomyositis (JDM), 25 had polymyositis (PM) and 22 had connective tissue disease-associated myositis (CTD myositis). Mean disease duration was 10.9 months. ANA was positive in 84 (68.9 %), and MSAs in 61 (49.2 %) patients. Among MSAs, autoantibodies to Mi2, synthetase (Jo1, PL7, PL12, EJ) and SRP were present in 26 (20.9 %), 29 (23.4 %) and 6 (4.8 %) patients, respectively. Prevalence of MAAs was as follows: antibodies to Ro52 in 45 (36.3 %), Ku and PM-Scl 75 in 13 (10.5 %) and PM-Scl 100 in 5 (4 %) patients. Anti-Mi2 antibodies were positively associated with DM (21/55, 38.2 %; p < 0.0001) and pharyngeal weakness (13/34, 38.2 %; p = 0.004) and negatively associated with ILD (0/28; p = 0.001). ILD and mechanics' hands were significantly more in patients with anti-synthetase antibodies (16/28, 57 % and 14/22, 63.6 %; p < 0.0001). Four of six patients with anti-SRP antibody showed poor response to multiple drugs. Higher prevalence of anti-Mi2 is probably related to higher proportion of patients with DM. Absence of ILD in patients with anti-Mi2 antibody suggests that it may protect against ILD. In Indian population also, anti-synthetase antibodies are associated with ILD, and anti-SRP antibodies with poor response to treatment.