Differentials
Sepsis
SIGNS / SYMPTOMS
Central nervous system or systemic signs/symptoms of infection.
Sepsis may be the primary diagnosis but may also be present (later in course) as a complication of NMS. Sometimes concurrent infections (e.g., respiratory or urinary tract infection) may further complicate diagnostic assessment.[6][12][46]
INVESTIGATIONS
Blood, urine, sputum, and other cultures may be positive for infective organisms.
Status epilepticus
SIGNS / SYMPTOMS
Nonconvulsive status epilepticus is difficult to distinguish clinically from NMS.
INVESTIGATIONS
Electroencephalogram may differentiate between status epilepticus and NMS.[47]
Drug misuse/overdose
SIGNS / SYMPTOMS
History of drug misuse, overdose symptoms.
INVESTIGATIONS
Diagnosis is usually based on history and physical exam. Stopping all possible medications, when appropriate, is important.
Catatonia
SIGNS / SYMPTOMS
Withdrawal, predominance of motor abnormalities, absence of hyperthermia, gradual evolution of presentation, potential history of prior episodes.
INVESTIGATIONS
Diagnosis is usually based on history and physical exam.
Serotonin syndrome
SIGNS / SYMPTOMS
Rapid onset after administration of a serotonergic drug, hyperreflexia, clonus, diarrhea.
INVESTIGATIONS
Diagnosis is usually based on history and physical exam.[48]
Mania
SIGNS / SYMPTOMS
Patients usually present with marked agitation, psychosis, and confusion.
INVESTIGATIONS
Diagnosis is usually based on history and physical exam.
Malignant hyperthermia
SIGNS / SYMPTOMS
Occurs in genetically susceptible people following exposure to anesthetics or depolarizing muscle relaxants, rapid onset, trismus.
INVESTIGATIONS
Diagnosis is usually based on history and physical exam.
Heat stroke
SIGNS / SYMPTOMS
Rapid onset, occurs during episodes of prolonged elevations in ambient temperatures; diaphoresis and muscle rigidity usually not present.
INVESTIGATIONS
Diagnosis is usually based on history and physical exam, and confirmed by muscle contracture test.
Metabolic conditions
SIGNS / SYMPTOMS
Various metabolic effects (e.g., dehydration, hyponatremia, hypokalemia) can cause delirium presentation.
INVESTIGATIONS
Basic and extended metabolic panels (e.g., serum electrolytes, osmolality, serum aminotransferases, and blood glucose) may be abnormal depending on the specific metabolic condition present.
Brain infarcts
SIGNS / SYMPTOMS
May mimic NMS.
INVESTIGATIONS
CT/MRI head may show signs of stroke.
Normal pressure hydrocephalus
SIGNS / SYMPTOMS
Slowing of gait, urinary urgency, possibly with cognitive impairment. Onset of symptoms is generally insidious (over months to years).
INVESTIGATIONS
CT/MRI head may show mild to moderate ventricular enlargement, periventricular leukomalacia, cerebral infarction, relative preservation of cortical gyri and sulci, aqueduct flow void, reduced diameter of the corpus callosum, and widened callosal angle.
Brain tumors
SIGNS / SYMPTOMS
May mimic NMS.
INVESTIGATIONS
CT/MRI head may show evidence of tumor.
Autoimmune encephalitis
SIGNS / SYMPTOMS
Anti-NMDA receptor encephalitis can mimic psychiatric disorders and prompt treatment with antipsychotic medications.
Patients may have signs and symptoms suspicious for NMS.
INVESTIGATIONS
Anti-NMDA-receptor antibodies.
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