General Medical Information

Myasthenia Gravis

Frank E. Lucente
Samir Shah
Roger Kula

Myasthenia gravis is caused by impaired transmission across the myoneural junction due to the presence of antibodies to the acetylcholine receptor. Onset occurs at all ages with clustering among young women and older men. This disease is characterized by weakness and abnormal fatigue of striated muscles. Remission and exacerbation are characteristic. Ocular muscles are involved in more than 90% of these patients. There often is weakness of facial, laryngeal, and pharyngeal muscles. The cricopharyngeal muscle often is involved. The weakness is greater after exercise or at the end of the day. Nystagmus and vertigo are rare. Transient neonatal myasthenia gravis occurs among one in seven newborns born to a mother with myasthenia gravis. The infants are unable to suck and swallow. Diagnosis is made from the history and the findings of relief of weakness after administration of neostigmine (6). Myasthenia gravis is associated with thymoma among 10% of patients. The disease is autoimmune in nature and mediated by circulating immunoglobulin G antibodies to the acetylcholine receptor. A positive result for the presence of antiacetylcholine receptor antibody (present in approximately 85% of patients), a positive result of an edrophonium test, and abnormal results of repetitive stimulation electromyography are highly reliable in establishing the diagnosis.