Because coma demands immediate attention, the physician must employ an organized approach (Table 18-3). Almost all instances of coma can be traced to either widespread abnormalities of the bilateral cerebral hemispheres or to reduced activity of the reticular activating system in the brainstem.

TABLE 18-3: Differential Diagnosis of Coma
  1. Diseases that cause no focal brainstem or lateralizing neurologic signs (CT scan is often normal)
    1. Intoxications: alcohol, sedative drugs, opiates, etc.
    2. 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
    3. Severe systemic infections: pneumonia, septicemia, typhoid fever, malaria, Waterhouse-Friderichsen syndrome
    4. Shock from any cause
    5. Status epilepticus, nonconvulsive status epilepticus, postictal states
    6. Hyperperfusion syndromes including hypertensive encephalopathy, eclampsia, posterior reversible encephalopathy syndrome (PRES)
    7. Severe hyperthermia, hypothermia
    8. Concussion
    9. Acute hydrocephalus
  2. Diseases that cause focal brainstem or lateralizing cerebral signs (CT scan is typically abnormal)
    1. Hemispheral hemorrhage (basal ganglionic, thalamic) or infarction (large middle cerebral artery territory) with secondary brainstem compression
    2. Brainstem infarction due to basilar artery thrombosis or embolism
    3. Brain abscess, subdural empyema
    4. Epidural and subdural hemorrhage, brain contusion
    5. Brain tumor with surrounding edema
    6. Cerebellar and pontine hemorrhage and infarction
    7. Widespread traumatic brain injury
    8. Metabolic coma (see above) in the setting of preexisting focal damage
  3. Diseases that cause meningeal irritation with or without fever, and with an excess of WBCs or RBCs in the CSF
    1. Subarachnoid hemorrhage from ruptured aneurysm, arteriovenous malformation, trauma
    2. Infectious meningitis and meningoencephalitis
    3. Paraneoplastic and autoimmune meningitis
    4. Carcinomatous and lymphomatous meningitis

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