Myasthenia Gravis and Other Myasthenic Syndromes

Abstract

In this group of disorders transmission at the motor end-plates is abnormal. There are a number of possible abnormalities in motor endings which might result in inadequate neuromuscular transmission. These include abnormal synthesis of acetylcholine (ACh), defective release of ACh quanta, abnormalities in the neuromuscular cleft itself, abnormal post-synaptic ACh receptors and abnormal breakdown of ACh because of defective cholinesterase. However, although many of these possible sites of abnormality have been considered, at some time, in theories of the pathogenesis of the most common end-plate disorder, myasthenia gravis, abnormalities have been found only at some of these sites. In a number of congenital myasthenic syndromes discrete abnormalities in various components of the post-synaptic ACh receptor have been found, and in the Lambert—Eaton myasthenic syndrome release of ACh vesicles is abnormal (Table 12.1).