- Diseases that cause no focal brainstem or lateralizing neurologic signs (CT scan is often normal)
- Intoxications: alcohol, sedative drugs, opiates, etc.
- Metabolic disturbances: anoxia, hyponatremia, hypernatremia, hypercalcemia, diabetic acidosis, nonketotic hyperosmolar hyperglycemia, hypoglycemia, uremia, hepatic coma, hypercarbia, Addisonian crisis, hypo- and hyperthyroid states, profound nutritional deficiency
- Severe systemic infections: pneumonia, septicemia, typhoid fever, malaria, Waterhouse-Friderichsen syndrome
- Shock from any cause
- Status epilepticus, nonconvulsive status epilepticus, postictal states
- Hyperperfusion syndromes including hypertensive encephalopathy, eclampsia, posterior reversible encephalopathy syndrome (PRES)
- Severe hyperthermia, hypothermia
- Concussion
- Acute hydrocephalus
- Diseases that cause focal brainstem or lateralizing cerebral signs (CT scan is typically abnormal)
- Hemispheral hemorrhage (basal ganglionic, thalamic) or infarction (large middle cerebral artery territory) with secondary brainstem compression
- Brainstem infarction due to basilar artery thrombosis or embolism
- Brain abscess, subdural empyema
- Epidural and subdural hemorrhage, brain contusion
- Brain tumor with surrounding edema
- Cerebellar and pontine hemorrhage and infarction
- Widespread traumatic brain injury
- Metabolic coma (see above) in the setting of preexisting focal damage
- Diseases that cause meningeal irritation with or without fever, and with an excess of WBCs or RBCs in the CSF
- Subarachnoid hemorrhage from ruptured aneurysm, arteriovenous malformation, trauma
- Infectious meningitis and meningoencephalitis
- Paraneoplastic and autoimmune meningitis
- Carcinomatous and lymphomatous meningitis
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