Myopathy Associated With Antibodies to Signal Recognition Particle

OBJECTIVE: To characterize the clinical course of myopathy associated with antibodies to signal recognition particle (SRP), or anti-SRP myopathy. DESIGN: Case series. SETTING: Keio University Hospitals and National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan. PATIENTS: We reviewed clinical features of 27 patients with anti-SRP myopathy and analyzed disease progression and neurological outcome. MAIN OUTCOME MEASURES: Anti-SRP antibodies in serum were detected by RNA immunoprecipitation assay using extracts of K562 cells. RESULTS: Of the 27 patients, 5 (19%) showed chronic progressive muscle weakness as well as atrophy of limbs and trunk muscles from a younger age with more severe neurological outcomes compared with the other 22 patients(81%) with the subacute form. CONCLUSION: A subset of patients with anti-SRP myopathy can show a chronic progressive form associated with severe clinical deficits.