(D) The presence of at least three of altered mental status, agitation, tremor, shivering, diarrhoea, hyperreflexia, myoclonus, ataxia, or fever. Differential diagnoses include sepsis, neuroleptic malignant syndrome, sympathomimetic overdose, heat stroke, anticholinergic toxicity, delirium tremens, baseline psychiatric symptoms, and lethal catatonia. There is considerable overlap with neuroleptic malignant syndrome, and many patients may be taking both antidepressants and neuroleptic drugs. Patients with neuroleptic malignant syndrome tend to be more toxic, with a higher fever and myoclonus is uncommon, the muscle rigidity tending to be leadpipe. Severity ranges from mild, self limiting symptoms that spontaneously resolve to severe cases with rhabdomyolysis and renal failure. In one study, 70% of cases resolved within 24 hours, although 40% required intensive care unit admission.' Mortality is estimated at 1 1%. The basic principles of management are the prompt discontinuation of serotonergic medications and provision of adequate supportive care. With this management most cases resolve within 24 hours. Supportive care includes fluid resuscitation for dehydration, rhabdomyolysis and hypotension, and active cooling in high fever. Ifsymptoms are severe or persistent a number of drugs may be used, most ofwhich block postsynaptic serotonin receptors (table 16). Hyperthermia (temperature >40.50 C) indicates severe disease with significant complications and mortality. Drugs may be used to limit excessive muscle contraction, which contributes to fever, rhabdomyolysis, and musculoskeletal respiratory failure. The most widely used are benzodiazepines, particularly clonazepam, which will control myoclonus and prevent seizures. Theoretical arguments exist for the use of ,B blockers, which act at 5-HT1A receptors, in addition to their negative chronotropic effect. Several authors report successful treatment with chlorpromazine,7 a relatively potent 5HT2 antagonist, although it may lower the seizure threshold, as occurred in this case. Cyproheptadine is also reported to be effective." Management of complications such as seizures, ventricular tachycardia, or respiratory compromise involve standard techniques.