Myoclonus (nocturnus)

[Medically induced myopathia]

Muscular side effects of various anesthetics, analgetics, antibiotics, antihistaminic drugs, antiretrovirals, cardiotropics, immunosuppressants, lipid-lowering drugs, psychotropic drugs, anticancer drugs, and other substances are more frequent than assumed and are easily overlooked. Clinically, muscular side effects manifest as fatigue, myalgias, persistent or transient weakness, stiffness, intolerance to exercise, psychomotor slowing, muscle cramps, wasting, dyspnea, dysphagia, fasciculations, reduced tendon reflexes, impaired consciousness, myoglobinuria, renal failure, or hyperthermia. Diagnosis of these drug-induced myopathies is based on history, clinical neurologic examination, blood work, urine analysis, repetitive stimulation, electromyography, and muscle biopsy. A drug which induces muscular side effects should never be given again. Particularly in patients suffering from primary myopathy, myotoxic drugs should be applied with caution. The drugs which most frequently induce muscular side effects are steroids, statins, fibrates, antiretrovirals, immunosuppressants, colchicine, amiodarone, and anticancer drugs. Many drugs exhibit their myotoxic potential only in combination with other drugs or premorbid pathologic myogenic conditions.

Drug-induced and toxic myopathies

Drug-induced myopathies and, more rarely, rhabdomyolysis, are a common biological and clinical setting for clinical rheumatologists. The focus of this chapter is to review (i) the clinical presentation and management of these adverse drug reactions (ADR) according to pain and associated neurological symptoms, (ii) the common drugs prescribed by rheumatologists which may induce reactions such as ADR, with special reference to new drugs, (iii) the pathological classification associated with specific patterns, and (iv) the risk factors leading to myotoxicity (including genetic predisposition). Specific features to be reviewed include macrophage myofasciitis and biological agents of major importance when considering terrorist attacks with biological weapons. When diagnosis is suspected, discontinuation of the putative drug(s) is mandatory and should be carefully monitored.