Drug-induced myopathies in man

Abstract

Drug-induced diseases constitute up to 5% of hospital admissions,a figure which almost certainly understates the total morbidity due to drugs1. Sever drug-induced myopathies are uncommon, but milder forms may be more prevalent than is generally appreciated, since skeletal muscle constitutes some 45% of total body-weight and has a major metabolic role in addition to its mechanical function2. Knowledge of possible effects of drugs on the neuromuscular system is of increasing importance both because the range of therapeutic agents continues to expand and because the resulting syndromes, through usually reversible at the outset, may progress and lead to grave consequences if the drug responsible is not stopped. Drug-induced neuropathies3 will not be considered here, but it will be appreciated that muscle weakness may also be feature of such disorders and that some drugs may cause both a neuropathy and a myopathy. The features of the main drug-induced syndromes are summarised in the table. To these one could justifiably add the unwanted effects of srugs given for the treatment of central-nervous-system or neuromuscular disorders per se-e.g., the cholinergic block which may be produced by anticholinesterases alone or with corticosteroids in the myasthenic,4 and the profound weakness which may supervene after relief of spasticity with dantrolene sodium5.