Chapter 16 Antibody-mediated disorders of neuromuscular transmission

Abstract

Publisher Summary This chapter discusses the features of the antibodymediated disorders that affect neuromuscular transmission that include myasthenia gravis (MG), seronegative myasthenia gravis (SNMG), Lambert–Eaton myasthenic syndrome (LEMS), and acquired neuromyotonia (NMT). Electron microscopy shows an essentially normal motor nerve terminal, but the postsynaptic membrane lacks junctional folds, and there are reduced areas of contact between the presynaptic nerve terminal and the muscle membrane. About 10%–15% of all MG patients with generalized symptoms do not have detectable acetylcholine receptor (AChR) antibodies by current laboratory methods, and these patients are termed as “seronegative.” Seronegative patients respond well to plasma exchange, and their immunoglobulins passively transfer a defect in neuromuscular transmission to mice. LEMS is electrophysiologically distinct from MG. The compound muscle action potential (CMAP) is reduced in amplitude following supramaximal nerve stimulation with decrement at low rates of repetitive nerve stimulation, and increment at higher rates, or following a few seconds of voluntary contraction. LEMS is often associated with small cell lung cancer (SCLC) and is also sometimes found with paraneoplastic cerebellar degeneration and paraneoplastic encephalomyelitis.