The neuromuscular disorders described are divided into four groups: motoneuron diseases, peripheral neuropathies, disturbances of neuromuscular transmission and myopathies. In motoneuron diseases problems mainly result from respiratory insufficiency and the predisposition for aspiration caused by progressive muscular weakness. Depolarising muscle relaxants may elicit myotonic reaction and massive hyperkalemia. In contrast to non-depolarising muscle relaxants there may be an extreme hypersensitivity. In peripheral neuropathies the cardiac function is often limited whereby dysautonomia may enhance cardiovascular instability. The negative inotropic effect of anaesthetic agents must be observed with care and patients with higher degree of AV blocks may need a cardiac pacemaker during general anaesthesia. The Charcot-Marie-Tooth-Syndrome is characterized with a high sensitivity to thiopental. Disturbances of neuromuscular transmission frequently cause respiratory problems The fluctuating weakness of bulbar and respiratory muscles may impair swallowing and can lead to recurrent aspirations. Due to the reduced number of acetylcholine receptors the sensitivity to non-depolarizing muscle relaxants is elevated and the response to succinylcholine is reduced. Drugs reducing neuromuscular transmission such as antibiotics and beta-blockers may enhance these symptoms and should be avoided. In progressive muscular dystrophies the anaesthetic risk is mainly dependent on cardiac and respiratory impairment. Administration of succinylcholine leads to the risk of hyperkalmic cardiac arrest. Patients with metabolic myopathies are also at risk due to the involvement of cardiac muscle but respiratory problems are less frequent. Muscle metabolism should be supported by administration of substrates depending on the underlying disorder. In membrane disorders muscle rigidity (myotonic reactions) or weakness may lead to respiratory insufficiency. In addition to the depolarising muscle relaxants also anticholinesterase drugs, hypothermia and dyskalaemia can evoke myotonic reactions.
