Anti-SRP myopathy: Different entity from myositis

Anti-signal recognition particle (SRP) antibody, detected in 5-8% of patients with clinical diagnosis of myositis, had been associated with severe and refractory myositis. However, it has been accepted that anti-SRP myopathy should be separated from myositis based on histological features of necrotizing myopathy. We reviewed clinical features of 27 patients with anti-SRP myopathy, and analyzed disease progression and neurological outcome. Anti-SRP antibodies in serum were detected by RNA immunoprecipitation assay using extracts of K562 cells. Of the 27 patients, 5 (18.5%) showed chronic progressive muscle weakness as well as atrophy of limbs and trunk muscles from a younger age with more severe neurological outcomes compared to the other 22 patients with the subacute form. A subset of patients with anti-SRP myopathy can show a chronic progressive form associated with severe clinical deficits.