* Indicates potentially treatable causes


  1. *Acute bacterial meningitis
  2. *Viral encephalitis
  3. *Tuberculous meningitis
  4. *Cryptococcal meningitis
  5. *Tertiary syphilis (general paresis rarely seen today)
  6. Prion infections
    1. Creutzfeldt-Jakob disease
      • Diagnosis: Dementia, basal ganglia signs, startle myoclonus, etc.
      • Treatment: None
    2. Kuru
      • Diagnosis: . Cerebellar degeneration; dementia late; acquired by eating victims
      • Treatment: None
  7. Atypical virus infections
    1. Subacute sclerosing panencephalitis
      • Diagnosis: Dementia, myoclonus: under 20 years old (caused by measles-like virus); high CSF gamma globulin level
      • Treatment: None
    2. Progressive multifocal leukoencephalopathy
      • Diagnosis: Multifocal hemispheric signs usually in immunosuppressed patient (HIV, on immunosuppressive drugs or with malignancy particularly of reticuloendothelial origin)
      • Treatment: None


  1. Lack of substrate
    1. *Tissue hypoxia
      1. Low blood PO2
        • Diagnosis: Cyanosis; blood gases
        • Treatment: Oxygen, respiratory support; treat infection and spasm
      2. Severe anemia
        • Diagnosis: Hemoglobin, hematocrit
        • Treatment: Tranfusion, etc.
      3. Decreased perfusion
        1. Decreased cardiac output
          • Diagnosis: Hypotension; signs of congestive failure
          • Treatment: Appropriate cardiac medications or fluids for hypovolemia; treatment of septic shock, etc.
        2. Arterial obstruction
          • Diagnosis: Usually focal signs
          • Treatment: Support, anticoagulation if progressive without hemorrhage
        3. Increased viscosity (polycythemia)
          • Diagnosis: Hematocrit
          • Treatment: Phlebotomy
    2. *Hypoglycemia
      • Diagnosis: Varied clinical picture: often dizziness, syncope; but may have focal signs or seizures; low blood glucose; 5-hour glucose tolerance test to rule out reactive hypoglycemia
      • Treatment: IV glucose
    3. *Nutritional deficiency
      1. Vitamin B12 deficiency
        • Diagnosis: Pernicious anemia and/or spinal cord involvement (not always present); lab: low serum B12 levels; positive Schilling test; achlorhydria (usually)
        • Treatment: IM vitamin B12 administration
      2. Thiamine deficiency
        • Diagnosis: Wernicke's encephalopathy; confusion, amnesia, truncal ataxia, disconjugate eye movements; fatal if untreated: Korsakoff's psychosis (residual of Wernicke's): amnesia, confabulation
        • Treatment: IM/IV thiamine; vitamin treatment is only partially, if at all, effective for Korsakoff's
  2. Endocrine
    1. *Hypothyroidism
      • Diagnosis: Myxedema, hung-up reflexes, hypothermia; high TSH, low T4, etc.; hyponatremia
      • Treatment: Thyroid hormone replacement
    2. *Hyperthyroidism
      • Diagnosis: Weight loss, tremor, etc.; high T4, etc.
      • Treatment: Thyroid suppressants; surgery
    3. *Cushing's disease
      • Diagnosis: Hypertension, diabetes, Cushingoid features; hypokalemia; high cortisol
      • Treatment: Surgery
    4. *Parathyroid abnormalities
      1. Hyperparathyroidism
        • Diagnosis: Hypercalcemia (lethargy, etc.)
        • Treatment: Treat hypercalcemia; remove parathyroids
      2. Hypoparathyroidism
        • Diagnosis: Hypocalcemia; diffuse, soft tissue calcification; tetany
        • Treatment: Vitamin D
      3. Pseudohypoparathyroidism
        • Diagnosis: Hypocalcemia, skeletal abnormalities, basal ganglia calcification, tetany unusual despite very low calcium levels
  3. Electrolyte imbalance
    1. *Hyponatremia (water intoxication), inappropriate antidiuretic horome secretion, renal sodium wasting
      • Diagnosis: Lethargy, seizures, low serum sodium
      • Treatment: Water-restriction; hypertonic saline (sometimes)
    2. *Hypercalcemia
      • Diagnosis: Lethargy, confusion; high serum calcium
      • Treatment: Lower calcium (phosphate, steroids, mithromycin, etc.); treat underlying condition
    3. *Hypomagnesemia
      • Diagnosis: Confusion, seizures; in setting of persistent diarrhea (especially in infants), or of IV therapy without Mg supplements; serum Mg may not reflect deficiency; calcium usually also low
      • Treatment: Magnesium sulfate
    4. *Hypocalcemia
      • Diagnosis: Confusion; tetany seizures; serum calcium low
      • Treatment: Replace calcium; treat underlying condition
    5. *Hyperosmolar coma
      • Diagnosis: High blood glucose, severe dehydration with associated electrolyte abnormalities
      • Treatment: Fluids, insulin
  4. Toxic
    1. Endogenous
      1. *Hypercapnia (pulmonary insufficiency)
        • Diagnosis: Signs of respiratory insufficiency, asterixis
        • Treatment: Assist respirations, pulmonary toilet; antibiotics
      2. *Hepatic encephalopathy
        • Diagnosis: Lethargy, dementia, asterixis; hyperventilation with respiratory alkalosis (?central); high serum ammonia; high CSF glutamine; if chronic may see dementia plus choreiform movements and dystonia
        • Treatment: Treat infections, gastrointestinal bleeding (when present); cleanse bowel (neomycin enemas, acetic acid enemas, lactulose), L-dopa
      3. *Renal insufficiency
        • Diagnosis: Multifocal myoclonus, seizures, asterixis; signs of uremia; high BUN, creatinine
        • Treatment: Treat primary disease; dialysis
      4. *Acidosis
        • Diagnosis: Hyperventilation, low pH
        1. Diabetic ketoacidosis
          • Diagnosis: Hyperglycemia, ketosis
          • Treatment: Fluids, insulin, bicarbonate
        2. Lactic acidosis
          • Diagnosis: Acidosis without hyperglycemia, seen with sepsis, shock, idiopathic
          • Treatment: Treat underlying cause; bicarbonate
      5. *Wilson's disease
        • Diagnosis: Dystonia, choreiform movements; cirrhosis; high liver copper, low ceruloplasm; high urine copper excretion
        • Treatment: Copper-binding agent (penicillamine), low copper diet, liver transplant?
      6. *Hyperlipidemia
        • Diagnosis: Greatly increased serum cholesterol and triglycerides
        • Treatment: Lower serum lipids
      7. Limbic dementia (remote effects of carcinoma)
        • Diagnosis: Memory loss, agitation; may have cerebellar or brain stem signs
        • Treatment: None
    2. Exogenous toxins
      1. *Drugs
        • Diagnosis: Serum levels, history
        1. Hypnotics
          • Diagnosis: Ataxia, dementia, lethargy, comatose
          • Treatment: Reduce dose slowly if comatose; fluids, respiratory and blood pressure support; dialysis when appropriate; benzodiazepine antagonists (with caution for acute withdrawal)
        2. Aspirin
          • Diagnosis: Metabolic acidosis plus respiratory alkalosis
          • Treatment: Fluids; alkalinize urine
        3. Anti-convulsants
          • Diagnosis: Ataxia, dementia, lethargy
          • Treatment: Reduce dose
      2. *Toxins: Methanol, ethylene glycol, old paraldehyde
        • Diagnosis: Severe metabolic acidosis, blindness with methanol, hippurate crystals in urine with ethylene glycol
        • Treatment: Bicarbonate; ethanol for methanol intoxication

Vascular disease

  1. *Strokes (multiinfarct dementia)
  2. *Hypertensive encephalopathy
  3. *Vasculitis (lupus, etc.)


  1. *Mass lesions
    1. Neoplasms
      • Diagnosis: Focal signs, except in "silent areas" (i.e., frontal lobes); positive brain scan (over 80%); CT scan and MRI positive in most
      • Treatment: Surgery, XRT, Chemotherapy (depending on the type); steroids if edema
    2. Subdural hematoma
      • Diagnosis: Often headache, lethargy; mild focal signs; history of trauma (not always); increasing CSF protein; positive brain scan; positive CT scan
      • Treatment: Surgery
    3. Intracerebral hematoma
      • Diagnosis: Focal signs, usually; if hematoma is subcortical, in a silent area (less than 10% of spontaneous intracerebral hematomas), focal signs may be minimal; CT scan positive
      • Treatment: Surgery (in rare cases)
  2. *Hydrocephalus

"Degenerative" diseases

  1. Without elementary neurologic findings
    1. *Alzheimer's disease
      • Diagnosis: Memory loss usually prominent early; very common, the usual senile dementia; CT scan positive
      • Treatment: Symptomatic agents, ?Vitamin E
    2. Pick's disease
      • Diagnosis: Same; not clinically separable from Alzheimer's: can only be separated pathologically; very rare in United States
      • Treatment: None proven
  2. Demyelinating disease
    1. *Multiple sclerosis
      • Diagnosis: Evidence clinically of lesions separated in time and space; dementia common late in illness; frequently high CSF gamma globulin percentage of total CSF protein
      • Treatment: High dose steroids briefly in acute exacerbations; disease modifying drugs (see Chpt. 14)
    2. Schilder's disease
      • Diagnosis: Usually in children; dementia most prominent sign, but soon cortical blindness, long-tract signs, etc.
      • Treatment: None
  3. Inborn errors of metabolism
    1. Lipid storage diseases
      • Diagnosis: Tay-Sachs, etc.
      • Treatment: None
    2. Metachromatic leukodystrphy
      • Diagnosis: Dementia, peripheral neuropathy; absent arylsulfatase A
      • Treatment: None
    3. *Amino acidurias (many of them)
      • Diagnosis: Variable, urine for amino acids
      • Treatment: Restrictive diet for many
  4. Prominent basal ganglia or cerebellar signs.
    1. *Parkinsonism
      • Diagnosis: Typical basal ganglia signs (see chaps. 8 and 18)
      • Treatment: L-dopa (does not help dementia), amantidine, dopamine agonists
    2. Huntington's chorea
      • Diagnosis: Dementia may precede chorea; family history (autosomal dominant)
      • Treatment: None, control behavioral symptoms, genetic counseling
    3. Some spinocerebellar degenerations
      • Diagnosis: Cerebellar, posterior column, pyramidal, and peripheral nerve disease depending on which variant (Friedreich's ataxia most common example)
      • Treatment: None
    4. Myoclonic epilepsy (certain forms)
      • Diagnosis: Progressive form with Lafora's inclusion bodies produces dementia
      • Treatment: None; control seizures
    5. Parkinson-dementia complex (Guam)
      • Diagnosis: May be associated with ALS
      • Treatment: None
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