Neuroleptic Malignant Syndrome (NMS)

What happens in neuroleptic malignant syndrome

Dopamine helps control body temperature in the hypothalamus and muscle tone in the basal ganglia. When a drug suddenly blocks dopamine receptors strongly, or when dopamine medicine is abruptly withdrawn, the brain loses this control:

• muscle tone rises sharply, producing rigidity and heat
• the temperature set point and heat loss are disrupted
• the autonomic nervous system becomes unstable, so blood pressure, pulse and sweating swing widely

Rigid muscles break down (rhabdomyolysis), releasing CK and myoglobin, which can damage the kidneys.

Medicines that can cause NMS

• First-generation antipsychotics: haloperidol, fluphenazine and chlorpromazine carry the highest risk, especially by injection or as long-acting depot injections.
• Second-generation antipsychotics: risperidone, olanzapine, quetiapine, aripiprazole, clozapine and others. Risk is lower but not zero, and symptoms can be milder or atypical.
• Anti-nausea and gut medicines that block dopamine: metoclopramide, prochlorperazine, promethazine, droperidol.
• Withdrawal of dopamine drugs in Parkinson's disease, such as stopping levodopa suddenly before surgery or when someone cannot swallow.

Risk factors

• rapid dose increases, high doses or IV/IM injections
• dehydration, exhaustion and hot weather
• agitation and physical restraint
• combining antipsychotics with lithium
• a previous episode of NMS
• catatonia, brain injury, iron deficiency and alcohol withdrawal

Symptoms

NMS usually develops over 24 to 72 hours. The four hallmark features are:

1. Fever: typically above 38 °C (100.4 °F), often above 40 °C (104 °F)
2. Muscle rigidity: generalized "lead-pipe" stiffness, sometimes with tremor, difficulty swallowing or speaking
3. Altered mental status: confusion, agitation, drowsiness, mutism or coma. This often comes first
4. Autonomic instability: fast heart rate, high or fluctuating blood pressure, heavy sweating, rapid breathing and incontinence

How NMS is diagnosed

There is no single test. The diagnosis is made from the combination of drug exposure, typical symptoms and lab results, after ruling out other causes.

• Creatine kinase (CK): usually raised at least 4 times the upper limit, often into the thousands
• White cell count: often raised
• Kidney tests, electrolytes and urine myoglobin for rhabdomyolysis and acute kidney injury
• Low serum iron, a common finding
• Tests to exclude infection and other conditions: blood cultures, brain imaging, and a lumbar puncture to rule out meningitis or encephalitis

NMS vs serotonin syndrome and other lookalikes

See serotonin syndrome and malignant hyperthermia. Heat stroke, infection of the brain, lethal catatonia and drug withdrawal are also considered.

Treatment

NMS is treated in hospital, often in intensive care.

1. Stop the causing drug immediately, or restart dopamine medicine if withdrawal triggered it.
2. Cooling: cooling blankets, ice packs and cooled fluids. Acetaminophen (paracetamol) has limited effect because the fever is not set by infection.
3. IV fluids to correct dehydration and protect the kidneys from myoglobin.
4. Supportive care: oxygen, blood pressure control, prevention of blood clots, and breathing support if needed.
5. Benzodiazepines (lorazepam) for agitation and milder cases, especially if catatonia overlaps.
6. Specific drugs for moderate to severe cases: dantrolene, which relaxes skeletal muscle and reduces heat production, and bromocriptine or amantadine, which restore dopamine activity.
7. Electroconvulsive therapy (ECT) for cases that do not respond, or when NMS overlaps with catatonia.

Complications

• rhabdomyolysis and kidney failure
• aspiration pneumonia from swallowing problems
• blood clots in legs and lungs
• seizures, heart rhythm problems and heart attack
• respiratory failure
• disseminated intravascular coagulation (abnormal clotting and bleeding)

Recovery and restarting treatment

With oral drugs, NMS usually resolves in 7 to 10 days after stopping. After long-acting depot injections, it can last much longer. Most people recover fully, although some have lingering rigidity or cognitive effects for weeks.

Many people with NMS still need antipsychotic treatment for conditions such as schizophrenia. It can often be restarted safely if the team:

• waits at least 2 weeks after symptoms have fully resolved
• chooses a lower-potency or second-generation drug
• starts at a low dose and increases slowly
• avoids dehydration and depot injections
• monitors temperature, stiffness and CK closely

The chance of recurrence on rechallenge is significant, so this is planned carefully with the psychiatrist.

Frequently asked questions

What are the four main symptoms of neuroleptic malignant syndrome?

High fever, severe muscle rigidity, altered mental status such as confusion or reduced consciousness, and autonomic instability, meaning a fast heart rate, sweating and unstable blood pressure. They usually develop over 1 to 3 days after starting or increasing a dopamine-blocking drug.

How quickly does neuroleptic malignant syndrome develop?

It usually begins within the first 2 weeks of starting an antipsychotic or increasing the dose, although it can occur at any time during treatment. Once it starts, symptoms typically build over 24 to 72 hours, unlike serotonin syndrome, which develops within hours.

Can you die from neuroleptic malignant syndrome?

Yes. NMS is fatal in roughly 5 to 10% of cases today, usually from kidney failure, breathing problems, blood clots or heart complications. Early recognition, stopping the drug and intensive supportive care have greatly reduced deaths compared with the past.

How is NMS different from serotonin syndrome?

Serotonin syndrome develops within hours of a serotonergic drug and causes twitching, overactive reflexes, clonus, dilated pupils and diarrhea. NMS develops over days after a dopamine blocker and causes rigid, slow, lead-pipe stiffness with reduced reflexes. Treatments differ, so the distinction matters.

Can I take antipsychotics again after NMS?

Often yes, with precautions. Doctors usually wait at least 2 weeks after full recovery, choose a lower-risk drug, start at a low dose, increase slowly and monitor temperature, stiffness and CK. Tell every prescriber and anesthesiologist about your history of NMS.