creation date: 2026-06-19 01:16
tags: Pathologies
Neuroleptic Malignant Syndrome
Background
Definitions
Neuroleptic malignant syndrome (NMS) is a neurologic emergency associated with the use of antipsychotic agents.
The term neuroleptic is derived from high-potency first-generation antipsychotics, which were formerly known as neuroleptic agents.
Etiology & Risk Factors
Every class of antipsychotic drugs have been implicated in causing NMS. Additionally, some antiemetics (those that involve dopamine antagonism) are also associated.
Cases from these drugs can occur after initiation (single dose) or after many years of use and is not in a dose-dependent phenomenon, although higher doses increase risk. Additionally, a rapid dose escalation or switch of agents may contribute to risk.
Rarely, antiparkinson medication withdrawal can precipitate NMS.
Risk factors for precipitation are:
- Concomitant use of lithium or other psychotropic drugs
- Higher potency agents
- Depot formulations
- Comorbid substance use or neurologic disease
- Acute medical illness
Pathogenesis
The cause of NMS is unknown but based on clinical manifestations and the classes of drugs that precipitate the condition, the dopamine receptor blockade is heavily implicated.
Theories postulate dopamine antagonism destabilizes normal dopamine regulation of efferent sympathetic activity, leading to increased muscle tone, metabolism, and dysregulation of vasomotor and sudomotor activity.
Clinical Presentation
Signs & Symptoms
Symptoms consist of a tetrad that manifest and evolve over 1-3 days:
- Mental status change
- Agitated delirium with confusion
- Catatonic signs and mutism
- Profound encephalopathy with stupor and coma in severe cases
- Muscular rigidity
- Generalized and extreme “lead-pipe rigidity”
- Hyperthermia
-
38 C, even upwards of 40 C
-
- Autonomic instability
- Tachycardia (or other dysrhythmias)
- Labile or high bloop pressure
- Tachypnea
Rarer manifestations include:
- Dystonia
- Opisthotonus (abnormal posture from hypertonia)
- Trismus (painful spasms and tightness of jaw muscles)
- Chorea (involuntary, irregular muscle movements)
- Sialorrhea (excessive drooling)
- Dysarthria
- Dysphagia
History & Physical Exam
Diagnosis
Criteria
Diagnosis is made with characteristic clinical syndrome while taking an associated medication.
There are no validated criteria for degree of positive clinical and laboratory findings required to make a definitive diagnosis.
Work-up
Laboratory studies
Labs are used to rule out toxic-metabolic encephalopathy and systemic infection. Findings are generally nonspecific.
- Creatine kinase (elevated > 1000)
- CBC (leukocytosis)
- Lactate dehydrogenase (mildly elevated)
- Electrolytes (abnormalities are common: hypocalcemia, hypomagnesemia, hypo/hypernatremia, hyperkalemia, metabolic acidosis)
Additional evaluation
Brain imaging, lumbar puncture, and electroencephalography are not routinely used. They are obtained if a CNS infection or seizure is suspected.
Differential
Other diagnosis also characterized by rigidity, hyperpyrexia, dysautonomia, and an abnormal mental status are:
- Serotonin syndrome (serotonergic medications)
- Malignant hyperthermia (halogenated inhaled anesthetics and succinylcholine and family history)
- Catatonia (eval: behavioural prodrome, more positive motor phenomena)
- Withdrawal of intrathecal baclofen
- Anticholinergic syndrome
- Stimulant drug intoxication
Additionally, alternative neurologic and medical disorders should be considered:
- CNS infection
- Sepsis
- Seizures
- Paroxysmal sympathetic hyperactivity after severe head trauma
- Heat stroke (antipsychotic predisposes due to impaired thermoregulation)
- Acute dystonia
- Tetanus
- Acute alcohol withdrawal
- Thyrotoxicosis
- Pheochromocytoma
- Autoimmune encephalitis
- Acute porphyria
Red Flags / Complications
Most patients recover without neurologic sequelae. However, complications that can cause sequelae include:
- Severe hypoxia
- Elevated temperatures for long duration
Management
Management of NMS
Management setting depends on clinical severity and diagnostic certainty. At its extreme, NMS may require ICU care.
Stop causative agent
Substances contributing to NMS should be discontinued. If NMS was precipitated by dopaminergic therapy withdrawal, it should be reinstated.
Supportive care
- Maintain cardiorespiratory stability (may require mechanical ventilation)
- Fluids
- Control hyperthermia
- Lower blood pressure as needed
- Monitor and manage complications
Treatment of moderate or severe cases
Medications may be used based on clinical scenario. Efficacy is unclear and not proven by clinical trials. Options include:
- Lorazepam 1-2 mg IM or IV q4-6h
- Diazepam 10 mg IV q8h
- Dantrolene 1-2.5 mg/kg IV up to 10 mg/kg/day
- Bromocriptine 2.5 mg through NG tube q6-8h
- Amantadine 100 mg PO initially, then up to 200mg q12h
If pharmacologic treatment is inadequate, electroconvulsive therapy may be considered although its efficacy is unknown.
Restarting Antipsychotics
Risk of recurrent episode is present for patients who restart therapy. For patients who require the medication, the following can reduce the risk of recurrence:
- Hold medication for at least two weeks, longer if clinical features still present
- Use lower rather than higher-potency agents
- Start with low doses and titrate upwards gradually
- Avoid concomitant lithium
- Avoid dehydration