A case of an anti-SRP myopathy with enlargement of the thymus

A 54-year-old female was admitted to our hospital because of the Raynaud phenomenon and muscle weakness of the upper limbs. The neurological findings showed somatic and proximal limb weakness. Laboratory studies showed a high serum creatine kinase level. Computerized tomography (CT) revealed enlargement of the thymus. A muscle biopsy showed a small number of degenerating and regenerating fibers but no inflammatory infiltrations. At first, she was initially treated with a three-day course of intravenous methylprednisolone (1 g/day). However, the weakness progressed and the serum creatine kinase level remained high. She was subsequently treated with a combination of tacrolimus (3 mg/day) and prednisolone, but showed no any improvement of the muscle weakness. Following additional treatment with intravenous immunoglobulin, she showed improvement in her muscle weakness. Further, anti-signal recognition particle antibodies were identified after treatment. There have been no previous reports of myopathy with antibodies against the signal recognition particle and enlargement of the thymus, so we herein report the details of this unique case.