Test Background Positive antibodies against skeletal muscle are directed against the protein titin and the ryanomycin receptor. These are seen in a subgroup of patients with thymoma-associated myasthenia gravis. Their presence indicates a worse prognosis and poor response to thymectomy. It is more predictive of thymoma when accompanied by a muscle acetylcholine receptor (AChR) modulating antibody value of ≥90 % These antibodies may also be detected in patients with: Lambert-Eaton myasthenic syndrome (LES), small cell lung carcinoma (SCLC), breast carcinoma, patients treated with D-penicillamine, bone marrow transplant recipients having graft-versus-host disease, and autoimmune liver disorders.
Clinical Indications Diagnosis of thymoma, especially in patients with onset of myasthenia gravis younger than 45 years Screening test for myasthenia gravis in older patients, especially when tests for muscle AChR antibodies are negative Serial measurements are useful in monitoring the efficacy of immunosuppressant treatment in patients with myasthenia gravis Serial measurements in recipients of D-penicillamine or bone marrow allografts may be useful in monitoring autoimmune complications and graft-versus-host disease, respectively
Reference Range Negative
Sample Required RST (rust top)
Sample Volume 5-10 mL (1 mL serum)
Turnaround Time 28 days
Notes Not currently performed in house; this test is referred to the Protein Reference Unit, Sheffield.