Differentials
Brain tumors
SIGNS / SYMPTOMS
Focal neurologic signs.
INVESTIGATIONS
Head CT scan may show space-occupying lesion.
Subdural hematoma
SIGNS / SYMPTOMS
History of trauma, focal neurologic signs.
INVESTIGATIONS
Head CT scan may show hemorrhage.
Acute stroke
SIGNS / SYMPTOMS
Neurologic exam may show focal neurologic deficits in HE, but these are more common in stroke.
INVESTIGATIONS
Head CT scan may show hemorrhage or infarct.
Meningitis
SIGNS / SYMPTOMS
Headache, photophobia, neck stiffness, nausea, fever.
INVESTIGATIONS
Lumbar puncture may show cloudy cerebrospinal fluid with increased white blood cells and protein, and reduced glucose in meningococcal meningitis.
Organisms may be found on Gram stain and culture.
MRI may show meningeal enhancement.
Encephalitis
SIGNS / SYMPTOMS
Patient may have fever, headache, or history of infection (e.g., measles).
INVESTIGATIONS
Temporal lobe involvement on MRI is highly suggestive of herpes simplex virus encephalitis.
Cerebrospinal fluid may be normal or show lymphocytes.
Uremia
SIGNS / SYMPTOMS
History of renal disease or failure, fatigue, weakness.
Pallor, edema, hypertension, dyspnea, leg cramps, asterixis, and peripheral neuropathy may be present.
INVESTIGATIONS
Elevated serum BUN and creatinine are consistent with renal dysfunction and uremia.
Diabetic hypoglycemia
SIGNS / SYMPTOMS
Hypoglycemia is more common in older patients with diabetes or those attempting tight glycemic control.
Differentiating features include signs of autonomic overactivity, sweating, tachycardia, and coma.
INVESTIGATIONS
Serum glucose should be measured, as hypoglycemia can cause metabolic encephalopathy.
Nondiabetic hypoglycemia
SIGNS / SYMPTOMS
Common presenting symptoms include nausea, confusion, tremor, sweating, palpitations, or hunger. Patients may present with a nonspecific clinical history.
INVESTIGATIONS
Serum glucose should be measured; liver function and kidney function testing should be carried out to rule out hepatic and renal causes. If blood sugar is <50 mg/dL, additional tests should immediately be collected, including serum insulin, C-peptide, proinsulin, ethanol, beta-hydroxybutyrate, liver and kidney function tests, and levels of insulin secretagogues (sulfonylureas).
Hyperglycemia
SIGNS / SYMPTOMS
Diabetic ketoacidosis (DKA) may be preceded by polyuria, nausea, and confusion. Patients may have fruity-smelling acetone breath, tachycardia, and abdominal pain.
Hyperosmolar hyperglycemic state (HHS) may occur in the absence of ketones and may also cause metabolic encephalopathy.
INVESTIGATIONS
Serum glucose should be measured, as hyperglycemia can cause metabolic encephalopathy.
Blood and urine ketones are elevated and venous pH is reduced in patients with DKA.
Serum osmolality is elevated in patients with HHS.
Hypercarbia
SIGNS / SYMPTOMS
Signs of chronic respiratory failure.
INVESTIGATIONS
The normal level of PaCO₂ is generally accepted to be between 35 and 45 mmHg.
High levels can cause mental status changes.
Benzodiazepine overdose
SIGNS / SYMPTOMS
History of depression and suicidality may be present.
INVESTIGATIONS
Trial of flumazenil in selected patients may diagnose benzodiazepine overdose.
Tricyclic antidepressant overdose
SIGNS / SYMPTOMS
Tachycardia, hypotension may be present.
INVESTIGATIONS
ECG shows terminal 40-ms rightward axis deviation, seen as an R-wave deflection in aVR or an S-wave in lead I or aVL.
Opioid overdose
SIGNS / SYMPTOMS
History of opioid dependence. Bradypnea, miosis. May be signs of intravenous drug use such as fresh needle marks or old track marks.
INVESTIGATIONS
Dramatic improvement in consciousness level following naloxone administration.
Wernicke encephalopathy
SIGNS / SYMPTOMS
Characterized by encephalopathy, oculomotor dysfunction (nystagmus, gaze palsy), and gait ataxia.
INVESTIGATIONS
MRI typically shows bilateral, symmetric T2 and fluid attenuation inversion recovery (FLAIR) hyperintensities in the thalami, mammillary bodies, tectal plate, and periaqueductal area.[26]
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