Tests
1st tests to order
CBC
Test
Increased WBC count is common in NMS, but nonspecific. Increased WBC count can also indicate a differential diagnosis (e.g., sepsis).
Result
WBC count may be elevated
serum creatine kinase
Test
High levels may indicate rhabdomyolysis, with myoglobinuria, which may be severe enough to cause acute kidney injury. Creatine kinase is a highly sensitive but nonspecific marker of muscle tissue injury, and may be elevated in many other conditions (e.g., acute alcohol intoxication, acute psychosis). In the absence of known muscle trauma (seizure, prolonged immobility, etc.) the higher the level, the more likely that NMS is present.
Subsequent tests should be performed daily for monitoring until resolution.
Result
high levels (>500 units/L); levels above 180,000 units/L have been reported
basic metabolic panel
Test
Low sodium, high creatinine, high potassium may indicate differential diagnosis (e.g., acute kidney injury, and hydration status).
Result
usually normal in NMS
brain CT scan
Test
Key test in differential diagnosis. May show infection, mass, or bleed.
Result
usually normal in NMS; may reveal potential structural brain abnormality
brain MRI
Test
Key test in differential diagnosis. May show infection, mass, or bleed.
Result
usually normal in NMS; may reveal potential structural brain abnormality
myoglobin levels and urinalysis
Test
Myoglobinuria is a poor prognostic sign because it may herald multi-organ failure.
Urinalysis will help to determine whether a urine myoglobin test is needed (i.e., heme-positive with no red blood cells on microscopy).
Result
myoglobin may be present in urine and/or blood
urine culture
Test
To exclude sepsis.
Result
usually normal in NMS
blood culture
Test
To exclude sepsis.
Result
usually normal in NMS
lumbar puncture
Test
Key test in differential diagnosis. Cloudy cerebrospinal fluid, increased WBC count may indicate central nervous system infection (e.g., meningitis, encephalitis).
Result
usually normal in NMS
toxicology screen
Test
To rule out drug misuse/overdose (e.g., ecstasy).
Result
usually normal in NMS
chest x-ray
Test
To exclude pneumonia. Some patients with NMS are at increased risk for aspiration.
Result
usually normal in NMS
Tests to consider
serum iron
Test
Acute, transient low levels have been described, and in some cases appear to signal imminent worsening.[31]
Result
low levels
electroencephalogram
Test
Status epilepticus may present with behavioral and laboratory features that can be mistaken for NMS.
Result
intermittent or continuous focal or generalized ictal discharges
Use of this content is subject to our disclaimer