10 - Autoimmune diseases of the neuromuscular junction and other disorders of the motor unit

Summary

Myasthenia gravis

Introduction

As discussed by Drachman (1981), a patient with the features of myasthenia gravis (MG) was recorded by Willis in 1672. A full description of the disease was given in 1900 by Campbell & Bramwell, who described the clinical features, mentioning that the weakness frequently started with ptosis and diplopia. The concept that MG was an autoimmune disease was suggested by Simpson (1960), because MG was often associated with other autoimmune diseases. Nastuk, Plescia & Osserman (1960) also suggested an autoimmune pathogenesis for MG, on the basis of alterations in serum complement levels. The finding that injection of purified acetylcholine receptor (AChR) into rabbits caused an autoimmune disease similar to MG (Patrick & Lindstrom, 1973) was further evidence that MG has an immune aetiology. Most patients with MG have elevated levels of circulating antibodies to the AChR (Lindstrom et al., 1976c), although some patients do not (seronegative MG) (Birmanns et al., 1991). Seronegative MG (Birmanns et al., 1991; Lu et al., 1993) and MG induced by exposure to penicillamine (Heidenreich, Vincent & Newsom-Davis, 1988) also appear to have an autoimmune aetiology.

Clinical features

General clinical features

MG is a relatively uncommon disease. Kurtzke (1978) suggested that the prevalence of MG is about 4 per 100 000.