Progress in myasthenia gravis.

Abstract

Myasthenia is a syndrome of increased fatigability in striated muscle. It may occur with lesions of the central nervous system or with lesions of muscle. The muscle weakness in these dis orders is usually persistent and unrelenting. Myasthenia gravis, however, is a disorder of neuromuscular function due to a reduction of available acetylcholine (AC) receptors at the neuro muscular junction. The muscle weakness is characteristically worse after effort and improved by rest. The patient starts to comb her hair and is unable to finish, or halfway through a meal finds that she can chew no longer. The muscle weakness has a characteristic distribution, the extraocular, bulbar, neck, limb girdles, distal limbs, and trunk muscles being affected in that order. The myasthenia responds to cholinesterase inhibitors, which enhance the effects of the limited supply of AC at the neuromuscular junctions, and the quick-acting anticholinesterase edrophonium (Tensilon) provides a useful diagnostic test for myasthenia gravis. The diagnosis is not difficult so long as the possibility is kept in mind. When the distribution of muscle weakness is atypical psychiatric disease is commonly and erroneously diagnosed. The incidence of myasthenia gravis is about 1 in 30 000. There is a tendency to early remission but complete remissions are not prolonged and are rarely repeated. They usually occur in those patients with the ocular forms of the disease and within two years of its onset. Patients with the purely ocular form of myasthenia gravis do not commonly develop generalised myasthenia if symptoms remain confined to the extraocular muscles for more than a year, and this may be a distinct variety of the disease.