Myasthenia gravis

Myasthenia gravis is an autoimmune disorder mainly caused by antibodies to the muscle acetylcholine receptors (AChRs) at the neuromuscular junction. Loss of these receptors leads to a defect in neuromuscular transmission with muscle weakness and fatigue. AChR antibody tests are widely available and overall incidence and prevalence of the disorder seem to be rising, especially in elderly people. The disease is heterogeneous with respect to age at onset, thymic changes and distribution of muscle weakness, but the roles of immunogenetic factors and thymic abnormalities in the causes of the different forms are unclear. Most patients are now effectively treated with cholinesterase inhibitors and immunosuppressive drugs, and in younger patients by thymectomy. In about 15% of patients with myasthenia gravis, AChR antibodies are absent, and many of these patients have antibodies to another neuromuscular junction protein, muscle specific kinase (MuSK). Myasthenia needs to be distinguished from other rarer but equally well characterised autoimmune, genetic, and toxic disorders of neuromuscular transmission by clinical and laboratory tests.