14th February 2025

Diagnosis of NMS

Examination in NMS

Typical features on examination include:

• Altered conscious level, e.g. agitation, confusion, coma
• Autonomic instability, e.g. hyperthermia (sweating), tachycardia, tachypnoea, labile blood pressure, drooling
• Respiratory distress
• Muscle rigidity*: lead-pipe rigidity, dysphagia

Presentation of NMS is very similar to SS, and some drugs can cause both. The main discriminators are the longer onset time in NMS from drug initiation or dose change, and features marked with *.

Investigations in NMS

NMS is a clinical diagnosis with no specific test, although the below support diagnosis and screen for complications.

Bedside tests:

• ECG: NMS and associated metabolic changes and autonomic instability can trigger cardiac issues
• Urinalysis: myoglobinuria indicates poor prognosis

Blood tests:

• FBC, U&Es, LFTs, clotting, blood cultures: for AKI, electrolyte abnormalities, infection, liver failure
• Creatine kinase (CK): 4x above upper limit of normal range due to muscle damage (non-specific)
• Blood gas: screen for respiratory failure
• Blood glucose: rule out hypoglycaemia

Tests to rule out infection or other causes of confusion should be considered, e.g. CXR, CT head, LP.