INTRODUCTION — Neuroleptic malignant syndrome (NMS) is a life-threatening neurologic emergency associated with the use of antipsychotic (neuroleptic) agents and characterized by a distinctive clinical syndrome of mental status change, rigidity, fever, and dysautonomia.
Mortality results directly from the dysautonomic manifestations of the disease and from systemic complications. Mortality has declined from the earliest reports in the 1960s of 76 percent and is more recently estimated between 10 and 20 percent [1,2]. This probably reflects greater awareness of the disease, earlier diagnosis, and more aggressive intervention. Requiring a high clinical suspicion for diagnosis and treatment, NMS is appropriately a syndrome more often considered than truly diagnosed.
EPIDEMIOLOGY — Incidence rates for NMS range from 0.02 to 3 percent among patients taking antipsychotic agents [3,4]. This wide range probably reflects differences in the populations sampled, for example, inpatient versus outpatient psychiatric populations, as well as differences in the surveillance methods and definitions of disease used.
While most patients with NMS are young adults, the syndrome has been described in all age groups from 0.9 to 78 years [3,5-7]. Age is not a risk factor [8]. In most studies, males outnumber females twofold. Both age and sex distributions correspond with the distribution of the exposure to antipsychotic agents [5,8].
ASSOCIATED MEDICATIONS
Antipsychotic and antiemetic agents — NMS is most often seen with high-potency first-generation antipsychotic agents, formerly called neuroleptic agents (eg, haloperidol, fluphenazine) [9-11]. However, every class of antipsychotic drug has been implicated, including the low-potency (eg, chlorpromazine) and second-generation antipsychotic drugs (eg, clozapine, risperidone, olanzapine) as well as antiemetic drugs (eg, metoclopramide, promethazine, and levosulpiride) [5,12,13]. Associated medications are listed in the table (table 1).
While symptoms usually develop during the first two weeks of antipsychotic therapy, the association of the syndrome with drug use is idiosyncratic. NMS can occur after a single dose or after treatment with the same agent at the same dose for many years [14]. It is not a dose-dependent phenomenon, but higher doses are a risk factor [5]. Case-control studies implicate recent or rapid dose escalation, a switch from one agent to another, and parenteral administration as risk factors [1,8,15,16].
Associated risk factors — Case series and case-control studies also suggest that certain psychiatric conditions, acute catatonia, and extreme agitation are over-represented in patients who develop NMS [4,15-17]. It is possible that these represent conditions of higher risk simply because of the increased use of higher doses, rapid escalation, and parenteral therapy.
Other commonly listed risk factors, such as concomitant use of lithium or other psychotropic drugs, higher-potency agents, depot formulations, comorbid substance abuse or neurologic disease, and acute medical illness (including trauma, surgery, and infection), have not been substantiated in case-control studies [3,5,9,18-21]. It is also unclear whether dehydration, present in 92 percent of patients, is a risk factor for, as well as an early complication of, NMS [5,22].
Antiparkinson medication withdrawal — NMS is also seen in patients treated for parkinsonism in the setting of withdrawal of L-Dopa or dopamine agonist therapy, as well as with dose reductions and a switch from one agent to another [1,4,23-25]. Infection, dehydration, and surgery are possible precipitants as well [25,26]. This may be considered a distinct disorder from NMS and is sometimes called neuroleptic malignant-like syndrome or parkinsonism hyperpyrexia syndrome as well as acute akinesia or the malignant syndrome in Parkinson disease [26,27]. While some report that the clinical syndrome and laboratory findings are milder and the prognosis is better in this disorder [28], more severe cases and even fatalities have been reported [26,29,30]. In one series of 93 patients, 31 percent did not recover to their prior baseline [25].
PATHOGENESIS — The cause of NMS is unknown. Current theories are limited in their ability to explain all clinical manifestations and in supporting data. An animal model for NMS has been developed, but it does not fully correspond with the human syndrome [31,32].
Because of the class of agents with which NMS is associated, dopamine receptor blockade is central to most theories of its pathogenesis. Central dopamine receptor blockade in the hypothalamus may cause hyperthermia and other signs of dysautonomia [33,34]. Interference with nigrostriatal dopamine pathways may lead to parkinsonian-type symptoms such as rigidity and tremor [18,34]. Other neurotransmitter systems (gamma aminobutyric acid, epinephrine, serotonin, and acetylcholine) also appear to be involved, either directly or indirectly [31,35].
An alternative theory is that rigidity and muscle damage represent a primary effect on the peripheral muscle system, perhaps from direct changes in muscle mitochondrial function [18,36]. This in itself may represent a primary skeletal muscle defect or a direct toxic effect by these drugs on skeletal muscle.
A primary role has also been proposed for a disrupted modulation of the sympathetic nervous system, manifesting in increased muscle tone and metabolism and unregulated sudomotor and vasomotor activity; these in turn lead to ineffective heat dissipation, and labile blood pressure and heart rate [36]. In this model, dopamine antagonists precipitate symptoms by destabilizing normal dopamine regulation of efferent sympathetic activity.
Familial clusters of NMS suggest a genetic predisposition to the disorder [37]. Genetic studies have shown that the presence of a specific allele of the dopamine D2 receptor gene is over-represented in NMS patients [38]. This allele is associated with reduced density and function of dopamine receptors as well as decreased dopaminergic activity and metabolism.
CLINICAL MANIFESTATIONS — NMS is defined by its association with a class of medications that block dopamine transmission and a tetrad of distinctive clinical features: fever, rigidity, mental status changes, and autonomic instability (table 2) [4,39].
Typical symptoms — The tetrad of NMS symptoms typically evolves over one to three days. Each feature is present in 97 to 100 percent of patients:
●Mental status change is the initial symptom in 82 percent of patients [40]. It is not surprising, given the usual psychiatric comorbidity of the typical patient, that its significance is often underappreciated. This often takes the form of an agitated delirium with confusion rather than psychosis. Catatonic signs and mutism can be prominent. Evolution to profound encephalopathy with stupor and eventual coma is typical [17].
●Muscular rigidity is generalized and is often extreme. The increased tone can be demonstrated by moving the extremities and is characterized by "lead-pipe rigidity" or stable resistance through all ranges of movement. Superimposed tremor may lead to a ratcheting quality or a cogwheel phenomenon. Other motor abnormalities include tremor (seen in 45 to 92 percent), and less commonly, dystonia, opisthotonus, trismus, chorea, and other dyskinesias [3,5]. Patients can also have prominent sialorrhea, dysarthria, and dysphagia.
●Hyperthermia is a defining symptom according to many diagnostic criteria. Temperatures of more than 38°C are typical (87 percent), but even higher temperatures, greater than 40°C, are common (40 percent) [5]. Fever may be a less consistent symptom in patients with NMS associated with second-generation antipsychotic agents [41,42].
●Autonomic instability typically takes the form of tachycardia (in 88 percent), labile or high blood pressure (in 61 to 77 percent), and tachypnea (in 73 percent) [3,22]. Dysrhythmias may occur. Diaphoresis is often profuse.
In an analysis of 340 cases, 70 percent of patients followed a typical course of mental status changes appearing first, followed by rigidity, then hyperthermia, and autonomic dysfunction [40]. Some case reports document delay in the appearance of fever of more than 24 hours, leading to initial diagnostic confusion [3]. There is substantial variability in the presentation of NMS, and other reports do not necessarily substantiate a typical course.
Laboratory abnormalities
Elevated serum CK — Laboratory findings often reflect the clinical manifestations of NMS, with more severe rigidity leading to more profound creatine kinase (CK) elevation. In NMS, CK is typically more than 1000 international units/L and can be as high as 100,000 international units/L [3,4,18,22,43,44]. Normal CK can be seen if rigidity is not clearly well developed, particularly early in the onset of the syndrome. Elevated CK, particularly in the mild to moderate range, is not specific for NMS and is often seen in patients with acute and chronic psychosis due to intramuscular injections and physical restraints, and sometimes without specific explanation [36,43]. CK levels greater than 1000 international units/L, however, are probably more specific for NMS, and the degree of CK elevation correlates with disease severity and prognosis [3]. A case-control study demonstrated that patients with NMS were more likely to have had elevated CK levels during previous non-NMS admissions than did controls (76 versus 30 percent) [44]. CK levels do usually normalize after an NMS episode.
Other — Other laboratory abnormalities are common but nonspecific.
●A consistent laboratory finding is leukocytosis, with a white blood cell count typically 10,000 to 40,000/mm3 [3,5,22]. A left shift may be present.
●Mild elevations of lactate dehydrogenase, alkaline phosphatase, and liver transaminases are common.
●Electrolyte abnormalities: hypocalcemia, hypomagnesemia, hypo- and hypernatremia, hyperkalemia, and metabolic acidosis are frequently observed.
●Myoglobinuric acute renal failure can result from rhabdomyolysis [3,45]. (See "Rhabdomyolysis: Clinical manifestations and diagnosis".)
●A low serum iron concentration (mean 5.71 micromol/L; normal 11 to 32 micromol/L) is commonly seen in NMS patients and is a sensitive (92 to 100 percent) but not specific marker for NMS among acutely ill psychiatric patients [22,46].
Atypical cases — There is debate in the literature about milder or atypical cases of NMS. A "forme fruste" of the syndrome has been suggested to occur in milder cases, those associated with lower-potency agents, or those diagnosed early on. In particular, rigidity may be milder and perhaps even absent in these situations [47]. While many consider fever to be an essential feature of the diagnosis, cases are reported where it is absent [5]. Complicating this issue is the fact that the isolated appearance of dysautonomia, hyperthermia, parkinsonian rigidity, and CK elevations all occur with antipsychotic therapy. Individually they do not necessarily appear to be a harbinger of NMS [18,48]. From a practical clinical point of view, it seems reasonable to consider the diagnosis when any two of the tetrad of symptoms are present in the setting of an offending agent.
EVALUATION AND DIAGNOSIS — The diagnosis of NMS is made in a patient who is taking an associated medication (table 1) and who develops a typical clinical syndrome. An international multispecialty consensus group published diagnostic criteria for NMS in 2011 (table 3) [49]. These are based on positive clinical and laboratory findings as well as the exclusion of alternative causes, and each item is given a priority score for its relative importance in contributing to the diagnosis; however, no threshold score has been defined and validated for making a diagnosis of NMS. These criteria require independent validation before their use can be recommended in clinical practice. Other published criteria differ in requiring all or just some of the cardinal clinical and laboratory features [42].
Although there is no diagnostic test for NMS, testing has a crucial role in the evaluation of patients with potential NMS (table 2). Typical laboratory abnormalities help to confirm the clinical diagnosis, some tests rule out other conditions, and others are used to monitor patients for complications of NMS.
In patients with possible NMS, brain imaging studies and lumbar puncture are required to exclude structural brain disease and infection [47]. Magnetic resonance imaging (MRI) and computed tomography (CT) are typically normal. In isolated cases diffuse cerebral edema has been reported in the setting of severe metabolic derangements [50], as well as signal abnormalities in the cerebellum and basal ganglia that are similar to those seen in malignant hyperthermia (MH) [51]. Cerebrospinal fluid is usually normal, but a nonspecific elevation in protein is reported in 37 percent of cases [22].
Electroencephalography may be done to rule out nonconvulsive status epilepticus. In NMS patients, generalized slow wave activity is seen [4,22].
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of NMS can be broadly defined in two categories: those conditions that are related to NMS and those unrelated to NMS but commonly considered in the differential diagnosis.
NMS is one of a group of acute dysautonomias that share common features: rigidity, hyperpyrexia, and dysautonomia [5,7,47,52]. These entities are usually distinguishable, if only by the implicated drugs.
Serotonin syndrome — The most commonly diagnosed related disorder is serotonin syndrome [47,53,54]. This is usually caused by use of selective serotonin reuptake inhibitors and has a similar presentation that is difficult to distinguish from NMS [19]. Typical features in these patients that are not often seen in NMS patients are shivering, hyperreflexia, myoclonus, and ataxia [55,56]. Nausea, vomiting, and diarrhea are also a common part of the prodrome in serotonin syndrome and are rarely described in NMS. Rigidity and hyperthermia, when present, are less severe than in patients with NMS. While the symptoms of serotonin syndrome classically evolve more quickly than NMS, the speed of onset of both syndromes is variable and overlapping [57]. (See "Serotonin syndrome (serotonin toxicity)".)
Malignant hyperthermia — A rare genetic disorder, malignant hyperthermia (MH) is usually distinguished from NMS by its clinical setting: occurring with use of potent halogenated inhalational anesthetic agents and succinylcholine. However, MH has also been reported in patients with MH susceptibility who are exposed to heat stress or vigorous exercise. Its clinical appearance with hyperthermia, muscle rigidity, and dysautonomia is quite similar to NMS, although often more fulminant. Studies using muscle contracture testing to evaluate MH susceptibility among NMS patients have yielded conflicting results, with some finding a high and others a low prevalence of susceptibility. The test may be unreliable in the setting of acute or recent NMS [18,36,52]. (See "Malignant hyperthermia: Diagnosis and management of acute crisis".)
Malignant catatonia — Most problematic in the differential diagnosis of NMS, malignant catatonia shares clinical features of hyperthermia and rigidity with NMS. However, in this syndrome, there is usually a behavioral prodrome of some weeks that is characterized by psychosis, agitation, and catatonic excitement. The motor symptoms are also characterized by more positive phenomena (dystonic posturing, waxy flexibility, and stereotyped repetitive movements) than are described in NMS [58,59]. Laboratory values are more typically normal. The two disorders can be difficult to distinguish clinically, and historic details, particularly in the typical patient population, can be hard to elicit and interpret. The two syndromes may overlap; many case descriptions exist of NMS arising in patients with malignant catatonia [4,17]. One reviewer found it impossible to distinguish between the two disorders in 22 percent of cases [32]. (See "Catatonia in adults: Epidemiology, clinical features, assessment, and diagnosis", section on 'Malignant catatonia'.)
Other drug-related syndromes — Withdrawal of intrathecal baclofen therapy has been associated with an NMS-like syndrome in several case reports [60]. In these instances, the increased muscle tone is often described as rebound spasticity rather than rigidity. Otherwise, the spectrum of symptoms appears similar to NMS with dysautonomia, altered sensorium, fever, and elevated creatine kinase (CK) levels. Reduced gamma aminobutyric acid activity is believed to be the pathophysiologic cause. The symptoms reverse with reinstitution of therapy, and benzodiazepines may be helpful.
A central anticholinergic syndrome most often associated with intended or inadvertent drug overdose is better known. Patients present with encephalopathy and elevated body temperatures that are usually not as severe as NMS. Other features seen in NMS (diaphoresis, rigidity, and elevated CK levels) are absent here, while atypical features of NMS (flushing, mydriasis, bladder distension) are common. (See "Anticholinergic poisoning", section on 'Clinical features of overdose'.)
Acute intoxication with certain recreational drugs, especially cocaine and ecstasy (3,4-methylenedioxymethamphetamine [MDMA]), can be confused with NMS. Both potent stimulants of the central nervous system, these agents are attractive to abusers because they produce heightened vigilance, energy, and euphoria; however, these same effects can also manifest as psychomotor agitation, delirium, and even psychosis. Hyperthermia and rhabdomyolysis can develop, usually in association with increased physical exertion and ambient temperature. Rigidity is not common in these cases. MDMA use can also cause a serotonin syndrome. These syndromes are discussed in detail separately. (See "MDMA (ecstasy) intoxication" and "Cocaine: Acute intoxication" and "Methamphetamine: Acute intoxication".)
Other disorders — Alternative neurologic and medical disorders should be considered in the patient with NMS. Clinical symptoms of these disorders can overlap with NMS, particularly in patients who have extrapyramidal side effects of concomitant antipsychotic use. These diagnoses have serious prognostic and treatment implications and should not be overlooked [10,47]:
●Central nervous system infection (eg, meningitis, encephalitis)
●Systemic infections (eg, pneumonia, sepsis)
●Seizures
●Acute hydrocephalus
●Acute spinal cord injury
●Heat stroke (antipsychotics predispose to heat stroke by impairing thermoregulation)
●Acute dystonia
●Tetanus
●Central nervous system vasculitis
●Thyrotoxicosis
●Pheochromocytoma
●Drug intoxication, toxicity (eg, phencyclidine, ecstasy, cocaine, amphetamines, lithium)
●Withdrawal states
●Autoimmune or paraneoplastic encephalitis
●Acute porphyria
TREATMENT — The management of patients with NMS should be based upon a hierarchy of clinical severity and diagnostic certainty [4,32]. When manifestations are severe, intensive care unit monitoring and treatment are required (table 2).
Stop causative agent — Removal of the causative agent is the single most important treatment in NMS. Other potential contributing psychotropic agents (lithium, anticholinergic therapy, serotonergic agents) should also be stopped if possible. When the precipitant is discontinuation of dopaminergic therapy, it should be reinstituted.
Supportive care — The need for aggressive and supportive care in NMS is essential and uncontroversial [61]. Complications are common and severe, even fatal. These include:
●Dehydration
●Electrolyte imbalance
●Acute renal failure associated with rhabdomyolysis
●Cardiac arrhythmias, including torsades de pointes and cardiac arrest
●Myocardial infarction
●Cardiomyopathy
●Respiratory failure from chest wall rigidity, aspiration pneumonia, pulmonary embolism
●Deep venous thrombophlebitis
●Thrombocytopenia
●Disseminated intravascular coagulation
●Deep venous thrombosis
●Seizures from hyperthermia and metabolic derangements
●Hepatic failure
●Sepsis
The intensive nature of the required monitoring and supportive treatment is such that admission to the intensive care unit is required. The following supportive treatment should be provided:
●Discontinue any antipsychotic agent or precipitating drug.
●Maintain cardiorespiratory stability. Mechanic ventilation, antiarrhythmic agents, or pacemakers may be required [62].
●Maintain euvolemic state using intravenous fluids. Insensible fluid loss from fever and from diaphoresis should also be considered [63].
If creatine kinase (CK) is very elevated, high-volume intravenous fluids with urine alkalinization may help prevent or mitigate renal failure from rhabdomyolysis [64]. (See "Rhabdomyolysis: Clinical manifestations and diagnosis".)
●Lower fever using cooling blankets. More aggressive physical measures may be required: ice water gastric lavage and ice packs in the axilla. The use of acetaminophen or aspirin may have a role in reducing temperature in NMS, but it is not established. (See "Severe nonexertional hyperthermia (classic heat stroke) in adults".)
●Lower blood pressure if markedly elevated. The use of any specific agent over another is not supported by clinical data. Clonidine is effective in this setting [65]. Nitroprusside may have advantages by also facilitating cooling through cutaneous vasodilation [66]. (See "Drugs used for the treatment of hypertensive emergencies".)
●Prescribe heparin or low molecular weight heparin for prevention of deep venous thrombosis. (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients".)
●Use benzodiazepines (eg, lorazepam 0.5 to 1 mg) to control agitation, if necessary [32].
Specific treatments
Medical therapy — Medications are often used in patients with moderate or severe clinical manifestations of NMS. Recommendations for specific medical treatments in NMS are based upon case reports and clinical experience, not upon data from clinical trials. Their efficacy is unclear and disputed [67]. Commonly used agents are dantrolene, bromocriptine, and amantadine. We are more likely to use these agents in more severe cases and escalate treatment if there is no effect or the patient worsens. A reasonable approach is to start with benzodiazepines (lorazepam or diazepam) along with dantrolene in cases with moderate to severe muscle rigidity with elevated CK; bromocriptine or amantadine may also be added for patients with moderate to severe illness [68].
●Lorazepam, a benzodiazepine, is used 1 to 2 mg IM or IV every four to six hours.
Diazepam is dosed as 10 mg IV every eight hours.
In addition to mitigating agitation, benzodiazepines, particularly diazepam, may also have a muscle relaxant effect [18,47,69].
●Dantrolene is a direct-acting skeletal muscle relaxant and is effective in treating malignant hyperthermia (MH). Doses of 1 to 2.5 mg/kg IV are typically used in adults and can be repeated to a maximum dose of 10 mg/kg/day [70,71]. Efficacy includes reduction of heat production as well as rigidity, and effects are reported within minutes of administration. There is associated risk of hepatotoxicity, and dantrolene should probably be avoided if liver function tests are very abnormal. While some recommend discontinuing it after a few days, others suggest continuing for 10 to 14 days followed by a slow taper to minimize risk of relapse [72].
●Bromocriptine, a dopamine agonist, is prescribed to restore lost dopaminergic tone [68]. It is well tolerated in psychotic patients. Doses of 2.5 mg (through nasogastric tube) every six to eight hours are titrated up to a maximum dose of 40 mg/day. It is suggested that this be continued for 7 to 14 days after NMS is controlled and then tapered slowly.
●Amantadine has dopaminergic and anticholinergic effects and is used as an alternative to bromocriptine [21,73-76]. An initial dose is 100 mg orally or via gastric tube and is titrated upward as needed to a maximum dose of 200 mg every 12 hours.
●Other medications used with anecdotal success include levodopa (particularly in patients with NMS related to antiparkinson medication withdrawal) [25,34,77-80], apomorphine [81], carbamazepine [82], bupropion [83], and dexmedetomidine [84-86].
The use of any of these medications is controversial and supported only by anecdotal evidence. In an animal model of NMS, dantrolene reduced body temperature, CK levels, and an electromyography (EMG) activation measure of rigidity compared with control [31]. A retrospective analysis of published cases indicates that the use of bromocriptine and/or dantrolene appeared to hasten clinical response [87]. Time to complete recovery was reduced from a mean of 15 days (with supportive care alone) to 9 days (with dantrolene) and 10 days (with bromocriptine). Another analysis found reduced mortality: 8.6 percent in patients treated with dantrolene, 7.8 percent in patients treated with bromocriptine, and 5.9 percent in patients treated with amantadine compared with 21 percent in those receiving supportive care alone [76].
These and similar analyses are of questionable validity because of publication and other biases [1,76]. By contrast, a small prospective study in 20 patients showed that dantrolene and/or bromocriptine use was associated with a more prolonged course (9.9 versus 6.8 days) and a higher incidence of sequelae compared with those receiving supportive care alone [88]. However, the findings in this nonrandomized study could be explained by the fact that patients in the treated group were sicker than those not treated.
While evidence supporting the use of these agents is limited, they are frequently used because of anecdotal evidence of efficacy, lack of other proven treatments, and high morbidity and mortality of the disorder.
Electroconvulsive therapy — Electroconvulsive therapy (ECT) is generally reserved for patients not responding to other treatments or in whom nonpharmacologic psychotropic treatment is needed. (See "Overview of electroconvulsive therapy (ECT) for adults".)
The rationale for the use of ECT in NMS includes its efficacy in treating malignant catatonia and reports of parkinsonism improving with ECT. A further impetus for ECT comes from the frequent need for psychotropic therapy in a setting in which antipsychotics cannot be used.
ECT is a reasonable treatment option in NMS; however, there are no prospective, randomized, controlled data supporting its efficacy. A review of published cases found a lower mortality rate in ECT-treated patients compared with those receiving supportive care alone (10.3 versus 21 percent) [89]. In other literature reviews and case series, clinical response is described after an average of four treatments [90,91]. However, interpretation of these reports is complicated by the variable timing of ECT in relation to both symptom onset and resolution. While these results are interpreted as supporting ECT use in NMS, methodologic issues, including publication bias and lack of randomization, preclude conclusions about the efficacy of ECT in NMS.
There are safety concerns for ECT in NMS. Cardiovascular complications occurred in 4 of 55 patients, including 2 patients with ventricular fibrillation and cardiac arrest with permanent anoxic brain injury [90]. Another patient had status epilepticus. Other authors also report uncontrolled spontaneous seizures and aspiration pneumonia complicating ECT treatment for NMS [89,90,92].
The use of ECT in this setting is further challenged by the requirement for anesthesia. Because of concerns for associated MH, some authors suggest the use of nondepolarizing agents. However, in over 16 reported cases of NMS patients treated with succinylcholine, there was no MH [18,90]. Succinylcholine may also cause hyperkalemia and cardiac arrhythmias in patients with rhabdomyolysis and autonomic dysfunction [32].
PROGNOSIS — Most episodes resolve within two weeks. Reported mean recovery times are 7 to 11 days [5,22]. Cases persisting for six months with residual catatonia and motor signs are reported [6]. Risk factors for a prolonged course are depot antipsychotic use and concomitant structural brain disease [92]. Most patients recover without neurologic sequelae except where there is severe hypoxia or grossly elevated temperatures for a long duration.
Reported mortality rates for NMS vary between 5 to 20 percent [1,6,69,93]. Disease severity and the occurrence of medical complications are the strongest predictors of mortality [47]. A systematic review of published cases before 1989 revealed increased mortality in patients with myoglobinuria and renal failure compared with controls (50 versus 18.8 percent) [1]. Patients with neurologic disease including alcohol and drug addiction had a mortality of 38.5 percent. Others have documented lower mortalities associated with higher-potency versus lower-potency agents [6] and with atypical compared with typical antipsychotic drugs [93].
RESTARTING ANTIPSYCHOTICS — Patients restarted on antipsychotic agents may or may not have a recurrent NMS episode. It is difficult to quantify this risk from the available data. Different case series with variable duration of follow-up and various use of precautionary measures report relapse rates between 10 and 90 percent [1,5,14,94]. Early resumption of antipsychotic therapy; use of high-potency, parenteral antipsychotics; and concomitant use of lithium appear to be risk factors for recurrence [5,94]. Recurrent NMS is also idiosyncratic, with reports of patients with no sequelae after early resumption of a high-potency antipsychotic, and relapses of NMS occurring on low-potency agents up to two years later [14,94].
If antipsychotic medication is required, the following guidelines may minimize risk of NMS recurrence [4,22,94]; none of these guarantee either success or failure.
●Wait at least two weeks before resuming therapy, or longer if any clinical residua exist.
●Use lower- rather than higher-potency agents.
●Start with low doses and titrate upward slowly.
●Avoid concomitant lithium.
●Avoid dehydration.
●Carefully monitor for symptoms of NMS.
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Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Neuroleptic malignant syndrome (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Causes – Neuroleptic malignant syndrome (NMS) is a life-threatening neurologic emergency associated with the use of dopamine antagonists, and less commonly with dopamine agonist withdrawal. First-generation antipsychotic agents are most commonly implicated, but NMS can occur with any antipsychotic agent and also with antiemetic drugs (table 1). (See 'Associated medications' above.)
●Clinical manifestations – Cardinal clinical and laboratory features include (table 2) (see 'Clinical manifestations' above):
•Mental status change, which may take the form of an agitated or hypoactive delirium
•Muscular rigidity, which is characterized by generalized, "lead-pipe" rigidity
•Hyperthermia with temperatures typically above 38°C, sometimes higher
•Dysautonomia manifesting as tachycardia, labile blood pressure, tachypnea; arrhythmias may occur
•Elevated creatine kinase, the severity of which mirrors muscular rigidity, typically more than 1000 international units/L
●Differential diagnosis – Important considerations in the differential diagnosis include meningitis, encephalitis, systemic infections, heat stroke, and other drug-induced dysautonomias. (See 'Differential diagnosis' above.)
●Evaluation and diagnosis – NMS is a clinical diagnosis; no laboratory test can confirm the diagnosis. Testing is performed to rule out other conditions (table 2). Diagnostic criteria have been proposed (table 3). (See 'Evaluation and diagnosis' above.)
●Acute management – The management of patients with NMS is based upon a hierarchy of clinical severity and diagnostic certainty (table 2):
•Antipsychotic agents should be withheld if there is suspicion for NMS. Patients should have close inpatient monitoring of clinical signs and laboratory values. (See 'Supportive care' above.)
•Patients with significant hyperthermia and rigidity should be admitted to an intensive care unit setting and undergo aggressive supportive care as outlined above, as well as monitoring for potential dysautonomia and other complications. (See 'Supportive care' above.)
•For patients with creatine kinase (CK) elevations or hyperthermia on presentation and those who do not respond to withdrawal of medication and supportive care within the first day or two, we suggest medical therapy (Grade 2C). Benzodiazepines are typically initiated first to mitigate agitation and/or muscle rigidity; dantrolene and/or bromocriptine may be added depending on symptom severity. (See 'Specific treatments' above.)
•Electroconvulsive therapy (ECT) is an option in patients not responding to medical therapy in the first week, those in whom residual catatonia persists after other symptoms have resolved, and those in whom lethal catatonia is suspected as an alternative or concomitant disorder. (See 'Electroconvulsive therapy' above.)
●Resuming antipsychotic therapy – The risk of recurrent NMS following resumption of antipsychotic agents is uncertain. If antipsychotic medication is required, we attempt to minimize risk by following some general guidelines. (See 'Restarting antipsychotics' above.)
