AntiSRP

Anti-SRP, more commonly written as anti-SRP antibodies, are autoantibodies directed against the signal recognition particle, a ribonucleoprotein complex that guides nascent secretory and membrane proteins to the endoplasmic reticulum. SRP consists of a small RNA scaffold and several protein subunits, with SRP54 being a frequent target. Anti-SRP antibodies are most often identified in a subset of patients with autoimmune myopathy, particularly immune-mediated necrotizing myopathy (IMNM). They are detected in serum as part of autoimmune myopathy panels using assays such as immunoprecipitation, line blot, or ELISA.

Pathophysiology is not fully understood. The presence of anti-SRP antibodies is associated with a necrotizing pattern of muscle damage with little inflammatory infiltrate on biopsy, characteristic of IMNM. Whether the antibodies play a direct pathogenic role or primarily mark an underlying immune process remains a topic of investigation. Anti-SRP–associated myopathy is considered a distinct serologic subtype within NAM/IMNM.

Clinically, anti-SRP NAM typically presents with subacute proximal muscle weakness and markedly elevated serum creatine kinase levels. The disease can be more severe and rapidly progressive than some other inflammatory myopathies, and the response to corticosteroids alone is variable; many patients require additional immunosuppressive therapy or intravenous immunoglobulin. Cardiac involvement and interstitial lung disease are relatively uncommon but have been reported in rare cases.

Diagnosis relies on integrating clinical presentation, elevated CK, muscle biopsy showing necrotizing myopathy, and serologic evidence of anti-SRP antibodies. Anti-SRP is one of the principal serologic subtypes in IMNM, alongside antibodies such as anti-HMGCR. Management generally involves immunosuppressive regimens and supportive rehabilitation, with prognosis varying by individual.