This syndrome is an idiosyncratic, rare, and potentially fatal reaction most commonly associated with the use of antipsychotic drugs, although other drug classes also have been implicated. Clinical features include hyperthermia, muscle rigidity, autonomic instability, and alteration in mental status. Neuroleptic malignant syndrome (NMS) may occur at any time during therapy with the causative agent or may present when dopamine agonist therapy is discontinued. Risk factors include age (young or middle-aged adults are most commonly affected); a concomitant condition of exhaustion, dehydration, or a general debilitated state; and a history of NMS. 7 Typically, patients present with high fever, from 39°C to 42°C, but onset of hyperthermia may be delayed.78 Manifestations of autonomic dysfunction include tachycardia, labile hypertension, pallor, vasoconstriction, and diaphoresis. 9 A "lead-pipe" rigidity of the musculature is almost universal, while other manifestations of motor dysfunction also may occur, including tremors, myoclonus, dystonia, dyskinesia, dysphagia, dysarthria, and opisthotonus. Alteration in mental status ranges from confusion and agitation to stupor or coma.8 Characteristic laboratory findings include leukocytosis, myoglobinuria, and elevation of creatine phosphokinase; metabolic acidosis, renal insufficiency, electrolyte abnormalities, and elevated hepatic transaminases may also occur. The differential diagnosis includes meningoencephalitis, tetanus, collagen vascular disease, malignant hyperthermia, lethal catatonia, heatstroke, thyroid storm, pheochromocytoma, strychnine poisoning, and toxicity from a variety of drugs, including anticholinergic poisoning and the serotonin syndrome. 7,8 and 9 Perhaps the two syndromes most difficult to distinguish from NMS are malignant hyperthermia and lethal catatonia, as all three feature fever and muscle rigidity. Malignant hyperthermia is associated with causative exposure to certain anesthetic agents, whereas lethal catatonia, a type of heat exhaustion, follows a period of manic hyperactivity and does not feature autonomic instability.
The cornerstone of treatment of NMS is supportive care, with rapid cooling, fluid and electrolyte repletion, and critical care monitoring all being paramount ( Table
155-2). Intubation should be considered, and aggressive muscle relaxation should be pursued with intravenous benzodiazepines. The offending pharmacologic agent should be discontinued, or the previously withdrawn dopamine agonist should be restarted. 89 Dantrolene, a nonspecific skeletal muscle relaxer that is employed in the treatment of malignant hyperthermia, also has been used with good results, especially in cases wherein muscle rigidity is a predominant feature. 9i° Specific therapy for NMS has been advocated, some of which is based on the presumed pathophysiology of the syndrome, which is central dopamine depletion. 89 Bromocriptine, carbidopa/levodopa, and amantadine have been used with equivalent success, both alone and in combination. 919 Centrally acting dopamine agonists may be most important in the treatment of significant hyperthermia and mental status alteration, and vasodilators such as minoxidil and nitroprusside should be considered when vasoconstriction is a problem.9 Aggressive therapy has led to a reduction in mortality from NMS.7
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