Myasthenia Gravis and Other Immune-Mediated Disorders of the Neuromuscular Junction

Myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS), and neuromyotonia represent the three autoantibody-mediated disorders at the neuromuscular junction. They give muscle weakness and fatigability as their dominating symptoms. The weakness has usually a preferred localization to some but not all muscles. MG subgroups reflect pathogenesis and direct therapy. Patients should always be classified according to type of antibody, thymus pathology, age at symptom onset, and generalized versus pure ocular symptoms. LEMS and neuromyotonia are subgrouped according to paraneoplasia or not. All conditions have well-defined autoantibodies that bind in vivo and directly induce the muscle weakness. Therapy includes symptomatic drugs influencing the acetylcholine receptor activity in the postsynaptic membrane and immunosuppressive treatment influencing the pathogenic autoantibodies. This immunoactive treatment is not yet specific for the disease-inducing antigen-antibody interaction. Treatment is usually effective, and most patients obtain mild symptoms only or a clinical remission. Still patients tend to have a reduced quality of life, often side effects of their treatment, and they live with a risk of new exacerbations. Comorbidities need to be treated, especially a thymoma in paraneoplastic MG or neuromyotonia and a lung cancer in paraneoplastic LEMS. Supportive therapy is important, and a well-adapted daily training program is recommended. Severe exacerbations (myasthenic crisis) with the need for respiratory support are rare, occur mainly together with infections, and need immediate intensive care.