Coma

Question 1

Anatomy of Coma

Answer 1

• ARAS (esp cholinergic pedunculopontine fibers)—> thalamus —> cortex
• ARAS excites reticular thalamic nuclei —> inhibit the relay thalamic nuclei (transmission mode)
  - De-synchronized EEG (associated w/ wakefulness)
• If no ARAS excitation —> no inhibition of relay thalamic neurons (burst mode - not responsive to stimuli)
  - Synchronized EEG (associated w/ lack of wakefulness)

Question 2

Lethargy v Stupor v Coma

Answer 2

• Lethargy - mild sleep-like state; can wake w/ gentle stimulus
• Stupor - can be brought to somewhat wakeful state w/ vigorous stimulation
• Coma - unarousable and unresponsive; cannot induce wakefulness (even if some motor responses may exist)

Question 3

Types of Respirations & Localization (4)

Answer 3

• Cheyne-Stokes - crescendo-decresendo periods sometimes w/ apnea pauses between; localizes to hemispheres or diencephalon (can be intoxication, metabolic, CHF)
• Central Neurogenic Hyperventilation - sustained, heavy, rapid hyperventilation; localizes to midbrain
• Apneustic respirations - inspiratory cramps; localizes to pons always
• Ataxic respirations - uncoordinated rate and rhythm; RANDOM; localizes to lower pons or medulla

Question 4

3 Categories of Diseases Causing Coma

Answer 4

• Structural Lesions - visible changes - more focal effects
  
  • Supra-tentorial - mass lesions, meningitis, encephalitis, ischemic encephalopathy, subdural or epidural hematoma, large hemispheric infarction, brain abscess, neoplasm
  • Sub-tentorial - brainstem, thalamic or cerebellar hemorrhage, infarction or abscess
• Metabolic - no visible lesion- more widespread (MOST COMMON); Drug/alcohol intoxications, hypoglycemia, hepatic failure, shock, non-convulsive SE, heat stroke, hypoxia

Question 5

Signs of Supratentorial Lesion

Answer 5

• Signs - Cheyne Stokes breathing; normal eye movements b/c brainstem intact; normal pupils; hemiparesis
• If brainstem becomes involved LATER… poor reactivity of pupils (EWN), central neurogenic hyperventilation, incomplete eye movements, decerebrate or decorticate rigidity

Question 6

Signs of Subtentorial Lesion

Answer 6

• Signs - could cause coma, central neurogenic hyperventilation or apneustic respirations, absent eye movements for doll’s head or cold caloric test, abnormal posture or decerebrate rigidity

Question 7

Signs of Metabolic Coma

Answer 7

• Signs - pupils, eye movements and motor responses intact; not focal; random

Question 8

Changes in Eye Movements & Pupils in Coma (+ localization)

Answer 8

• Pupils
  
  • If diencephalon… parasymp fine but no sympathetic —> small pupils but reactive (EWN)
  • CN III lesion - dilated and non-reactive
  • Midbrain lesion - mid-position; poor or non-reactive pupils
  • Pontine lesion - pinpoint pupils (also narcotics)
  • Metabolic disorders - usually pupils are still reactive even if they are small
• Eye Movements
  
  • Brainstem lesion —> absent movement to doll’s eyes maneuver and no nystagmus in cold caloric stimulation