Myasthenia Gravis with Anti-Acetylcholine Receptor Antibodies

Abstract

Autoimmune myasthenia gravis (MG) is a disorder of the neuromuscular junction caused in the majority of patients by autoantibodies directed against the postsynaptic nicotinic acetylcholine receptor (AChR). The classic clinical presentation of MG has been well characterized as fluctuating muscle weakness affecting particular muscle groups. Selective review of the literature relating to the pathogenesis, diagnosis, and treatment of anti-AChR-positive MG. Approximately 85% of patients with generalized MG and 50% of patients with purely ocular MG have anti-AChR antibodies. A number of clinical MG subtypes may be identified amongst those patients with anti-AChR antibodies, comprising early-onset MG (onset < or = 40 years), late-onset MG (onset after 40 years), thymoma-associated MG, and ocular MG. 'Low-affinity' anti-AChR antibodies may be found in 66% of patients with generalized MG who are negative for anti-AChR and anti-muscle-specific receptor tyrosine kinase antibodies by conventional assays. While pathologic changes in the thymus gland (hyperplasia and neoplasia) almost certainly play a role in the development of MG in patients with early-onset disease and thymomatous MG, the pathogenic role of the thymus remains to be determined in ocular MG, late-onset MG, and generalized MG with low-affinity anti-AChR antibodies. Autoimmune MG with AChR autoantibodies encompasses several disease subtypes defined by clinical presentation and thymic pathology. Treatment options include thymectomy, cholinesterase inhibitors, immunosuppressive drugs and plasma exchange or intravenous immunoglobulin, and are tailored according to the clinical presentation.