ABSTRACT
Myasthenia gravis (MG) is an autoimmune disease. The majority of patients (~90%) have antibodies to the nicotinic acetylcholine receptors in the postsynaptic membrane of the neuromuscular junction, although the correlation between absolute antibody levels and disease severity is weak. Muscarinic acetylcholine receptors, and thus the autonomic nervous system, are spared. Thymus disease is associated with MG; 75% of patients have histological evidence of an abnormality (e.g. germinal centre hyperplasia), whilst 10% have a benign thymoma. Other autoimmune disorders are associated with MG (e.g. thyroid disease, pernicious anaemia), as are certain HLA subgroups. The prevalence of MG is around five per 100000 population, with young women being affected most commonly (peak onset 20-30 years of age). Men over the age of 50 are the next most commonly affected, though most patients with a thymoma associated with MG fall in this group. Critical care may be required for patients with MG under the following circumstances:
• In crisis (myasthenic or cholinergic). • With resultant respiratory failure. • Following pulmonary aspiration. • With a complication of immunosuppressive therapy. • For postoperative care following a thymectomy.
