Drug‐induced neurological disorders

Flinders Medical Centre, Bedford Park, SA 5042. Associate Professor Richard J Burns, BM BS, FRACP, FRCP(Lond), Senior Director of Neurology, Associate Professor of Medicine. Royal Melbourne Hospital, Grattan Street, Parkville, VIC 3050. David W Schultz, MB BS, Neurology Registar. No reprints will be available. Correspondence: Professor Richard J Burns. I t is sound medical practice to obtain a patient's complete drug history and never to discount the possibility that medication might explain any unusual or unexpected symptom or sign, or that drugs might be contributing to the underlying illness. Disorders of the nervous system can declare themselves in a wide variety of ways, and those that are drug induced are no exceptlon.'> Some, such as the neuroleptic malignant syndrome, are quite distinct. Others, such as headache or seizures, are less specific and hence drugs are just one of a number of possible causes. It is not the purpose of this review to consider every single drugrelated neurological disorder, but rather to highlight the common and clinically important disorders that are frequently not recognised. There are two major categories of drug reaction. The first consists of exaggerated or dose-related pharmacological responses such as drowsiness, ataxia and nystagmus, induced by anticonvulsants. As these drugs are usually prescribed for a neurological or psychiatric illness, their adverse reactions are more readily recognised because of the prescriber's familiarity with the drugs and their pharmacological actions. The second category is the idiosyncratic reaction, which is less predictable, especially in the setting of a non-neurological disorder. Antibiotic-induced meningitis is an example. It is easy to see how these unexpected reactions, especially if reported infrequently, can be misdiagnosed or overlooked. Those drug reactions which affect peripheral and cranial nerves, muscles, and the neuromuscular junction will not be considered in this review. Rather, those which can be generally attributable to the central nervous system the brain and spinal cord are discussed. The important ones are headache, parkinsonism and movement disorders, cerebral infarction and haemorrhage, benign intracranial hypertension, seizures, and altered mental states including coma. Reye's syndrome, the neuroleptic malignant syndrome, and drug-induced leukoencephalopathy are included in the more specific disorders.