Serotonin syndrome and NMS

Also called Neuroleptic malignant syndrome, NMS

Two rare, life-threatening drug reactions. Both present as fever plus confusion plus muscle changes, and both are missed.

What it is

These are two separate emergencies caused by psychiatric medication, and they belong together because they are confused with each other and because both are frequently mistaken for an infection or a worsening of the underlying illness.

Serotonin syndrome is caused by too much serotonin activity, usually when a serotonergic drug is started, increased, or combined with another. Antidepressants, tramadol, triptans, linezolid, lithium and St John's wort can all contribute. It develops fast, over hours.

Neuroleptic malignant syndrome is caused by dopamine blockade, usually from antipsychotics, and develops more slowly over days. It also occurs when Parkinson's medication is stopped abruptly.

Both can kill. Both are treatable if recognised.

Signs you might notice

Serotonin syndrome: agitation, confusion, fever, sweating, dilated pupils, diarrhoea, and crucially overactive reflexes and muscle twitching, particularly in the legs. Onset within hours of a dose change.

Neuroleptic malignant syndrome: high fever, severe muscle rigidity described as lead-pipe, confusion or reduced consciousness, unstable blood pressure and pulse, and sweating. Onset over days.

The distinguishing muscle sign: twitchy and hyperreflexic in serotonin syndrome, rigid in NMS.

Both cause muscle breakdown, which damages the kidneys.

How it can affect day-to-day life

The setting where these are most often missed is a care home or a mental health unit, where fever and confusion in somebody on antipsychotics gets treated as a urinary tract infection or as their psychosis worsening.

Any recent medication change is the clue. Ask what has changed in the last week, every time.

Abruptly stopping Parkinson's medication, including during an admission where the ward cannot supply it, can precipitate NMS. That is a documented and preventable cause.

Supporting someone well

Ask what has changed. New drug, increased dose, new combination, or a Parkinson's medicine stopped or delayed.

Treat fever plus confusion plus a muscle change in somebody on psychiatric medication as an emergency, not as an infection to be treated with antibiotics and observed.

Say the words at the hospital: "could this be serotonin syndrome" or "could this be NMS". Naming it changes the assessment.

Never stop Parkinson's medication abruptly, and make sure hospitals continue it on time. See Parkinson's disease.

Check for interacting drugs before adding any new medicine to an antidepressant, including tramadol and over-the-counter St John's wort.

Record temperature and muscle tone, not just behaviour.

Where to get help

999. Both are medical emergencies needing hospital assessment.

Tell the ambulance crew and the hospital exactly which medicines were taken and what changed recently.

Afterwards, ask for a written record of the reaction and which drugs to avoid.