Neuroleptic malignant syndrome

Keywords and synonyms: NMS

Overview
Neuroleptic malignant syndrome (NMS) is a life-threatening, neurological disorder most often caused by an adverse reaction to neuroleptic or antipsychotic drugs.

Historical Perspective
NLM was known about as early as 1956, shortly after the introduction of the first phenothiazines, and is derived from the French syndrome malin des neuroleptiques.

Pathophysiology
The mechanism is thought to depend on decreased levels of dopamine due to:
 * Dopamine receptor blockade
 * Genetically reduced function of dopamine receptor D2

Causes
NMS is caused almost exclusively by antipsychotics, including all types of neuroleptic medicines along with newer antipsychotic drugs. The higher the dosage, the more common the occurrence. Rapid and large increases in dosage can also trigger the development of NMS. Other drugs, environmental or psychological factors, hereditary conditions, and specific demographics may cause greater risk, but to date no conclusive evidence has been found to support this. The disorder typically develops within two weeks of the initial treatment with the drug, but may develop at any time the drug is being taken. NMS may also occur in people taking a class of drugs known as dopaminergics when the dosage is reduced (i.e Levodopa).

Symptoms
The first symptom to develop is usually muscular rigidity, followed by high fever and changes in cognitive functions. Other symptoms can vary, but may be unstable blood pressure, confusion, coma, delirium, muscle tremors, etc. Once symptoms do appear, they rapidly progress and can reach peak intensity in as little as three days. These symptoms can last anywhere from eight hours to forty days.

Laboratory Studies
A raised creatine phosphokinase (CPK) plasma concentration will be reported due to increased muscular activity. The patient may be hypertensive and suffering from a metabolic acidosis.

EEG Studies
A non-generalised slowing on an EEG is reported in around 50% of cases.

Unfortunately, symptoms of NMS are sometimes misinterpreted by doctors as symptoms of mental illness, delaying treatment.

Mnemonic
A mnemonic used to remember the features of NMS is: FEVER.
 * F - Fever
 * E - Encephalopathy
 * V - Vitals unstable
 * E - Elevated enzymes (elevated CPK)
 * R - Rigidity of muscles

Prognosis
As with most illnesses, the prognosis is best when identified early and treated aggressively. In these cases NMS is usually not fatal, although there is currently no agreement on the exact mortality rate for the disorder. Studies have given the disorder a mortality rate as low as 5% and as high as 76%, although most studies agree that the correct percentage is in the lower spectrum, perhaps between 10% - 15%. Re-introduction to the drug that originally caused NMS to develop may also trigger a recurrence, although in most cases it does not.

Treatment
Although treatment is not always necessary, it will help to cure the disease and prevent fatal developments from occurring. The first step in treatment is generally to remove the patient from any neuroleptic or antipsychotic drugs being taken and to treat fever aggressively. Many cases require intensive care, or some kind of supportive care at the minimum. Depending on the severity of the case, patients may require other treatments to contend with specific effects of the disorder. These include circulatory and ventilatory support, the drugs dantrolene sodium, bromocriptine, apomorphine and electroconvulsive therapy (ECT) if medication fails.

Differential diagnosis

 * Infection (sepsis, SIRS)
 * Serotonergic syndrome
 * Delirium tremens
 * Heat Stroke
 * Malignant hyperthermia

NMS and serotonergic syndrome
The clinical features of NMS and serotonergic syndrome are very similar. This can make differentiating them very difficult.

Features, classically present in NMS, that are useful for differentiating the two syndromes are:
 * Fever
 * Muscle rigidity
 * Laboratory Values (WBC & CK)