Coma & Related Disorders of Conciousness

Question 1

Definitions and classifications of acute disorders of consciousness?

Answer 1

Definitions
• Consciousness: Awareness of self and surroundings.
• Arousal: Level of consciousness (assessed via eye-opening and sleep-wake cycle).
• Awareness: Ability to interact with the environment (tested via command-following).

Classification of Acute Disorders of Consciousness
1. Coma: Complete unresponsiveness, no arousal, no awareness.
2. Stupor: Severe impairment, but responsive to strong stimuli (pain).
3. Drowsiness: Milder impairment, brief periods of awareness.
4. Acute Confusional State: Preserved consciousness but altered content (e.g., delirium, disorientation).

Question 2

Pathophysiology and mechanism?

Answer 2

Pathophysiology
Altered Level of Consciousness (Coma, Stupor, Drowsiness)
• Cause: Disruption of the ascending reticular activating system (ARAS) in the brainstem.
• Affected regions: Brainstem, midbrain, thalamus (relay station).
Altered Content of Consciousness (Acute Confusional State)
• Cause: Dysfunction of higher cortical structures (thalamus, hypothalamus, amygdala).
• Mechanism: Peripheral sensory input reaches the brain but is not processed correctly.

Pathophysiological Mechanisms
1.Symmetrical (Non-Structural) Causes (Diffuse metabolic/toxic insults)
• Exogenous causes: Toxins (lead, CO), drugs (sedatives, alcohol, opioids), infections (meningitis, encephalitis).
• Endogenous causes: Hypoxia, hyper/hyponatremia, hyper/hypoglycemia, ketoacidosis, Wernicke encephalopathy.
2. Symmetrical, Structural Causes (Bilateral brain damage)
• Supratentorial (above the tentorium cerebelli)
• Thalamic hemorrhage
• Bilateral internal carotid occlusion
• Hydrocephalus
3. Asymmetrical, Structural Causes (Unilateral damage with ARAS compression)
• Hemispheric stroke
• Brainstem lesions
• Cerebellar masses

Question 3

What is the ascending reticular activating system?

Answer 3

The Ascending Reticular Activating System (ARAS) is a crucial neural network located in the brainstem that regulates wakefulness, consciousness, and arousal. It is responsible for maintaining alertness and facilitating sensory processing, ensuring that the brain remains responsive to external stimuli.

Function
• Regulates Wakefulness: Maintains a state of alertness necessary for responding to stimuli.
• Modulates Sleep-Wake Cycle: Promotes wakefulness during the day and facilitates sleep at night.
• Enhances Sensory Perception: Filters and prioritizes sensory information before relaying it to the cortex.
• Maintains Consciousness: Enables awareness of self and surroundings

Question 4

Evaluation of coma?

Answer 4

1. History Collection : since the patient is in a coma, history must be gathered from family, bystanders, medical records, or personal belongings. Key aspects to assess:
   Onset of Coma:
   • Abrupt (seconds-minutes): Suggests vascular causes (e.g., hemorrhage, stroke).
   • Gradual (hours-days-weeks): Suggests tumors, infections, metabolic disorders.
   • Fluctuating: Typical of metabolic causes (e.g., diabetes, liver/kidney failure).
   Context in which the patient was found:
   • Trauma (head injury, fall, accident).
   • Seizures (postictal state).
   • Loss of sphincter control.
   • Presence of blood (suggests trauma or seizure).
   Previous Medical History:
   • Neurological conditions (stroke, epilepsy, neurodegenerative diseases).
   • Metabolic disorders (diabetes, liver/kidney failure).
   • History of substance abuse, overdose, or poisoning.
   • Psychiatric history (suicide attempts, drug overdose).
   • Recent illness, fever, infections (suggests meningitis, sepsis, encephalitis.
2. General Evaluation : a systematic assessment of vital signs and physical condition is crucial:
   Blood Pressure:
   • Hypertension: Suggests hemorrhage, hypertensive encephalopathy, increased ICP.
   • Hypotension: Suggests shock (sepsis, cardiac failure, hemorrhage, overdose).
   Heart Rate:
   • Tachycardia: Suggests shock, hypoxia, metabolic derangement.
   • Bradycardia: Seen in intracranial hypertension, drug intoxication (opioids, beta-blockers).
   Temperature:
   • Hyperthermia (>38°C): Suggests infection (sepsis, meningitis, encephalitis), heat stroke, drug overdose (anticholinergics, amphetamines).
   • Hypothermia (<35°C): Seen in cold exposure, hypothalamic dysfunction, alcohol/drug intoxication, sepsis.
   Respiratory Pattern Analysis: (Provides insight into brainstem involvement.)
   • Cheyne-Stokes breathing: Forebrain dysfunction (e.g., stroke, metabolic disorders).
   • Central neurogenic hyperventilation: Midbrain dysfunction (suggests trauma, tumor, stroke).
   • Apneustic breathing (deep, prolonged inspiratory pauses): Pontine lesion.

Question 5

Neurological examination in comatose patient?

Answer 5

Level of Consciousness
Use the Glasgow Coma Scale (GCS) to quantify coma severity:
• Eye Opening (E): 1-4
• Verbal Response (V): 1-5
• Motor Response (M): 1-6
• GCS ≤ 8: Indicates need for intubation (inability to protect the airway).

Brainstem Reflexes
• Pupillary Reflex (CN II & III):
• Dilated, fixed pupils: Suggests brain herniation, midbrain damage, atropine overdose.
• Pinpoint pupils: Seen in pontine damage, opioid overdose.
• Asymmetric pupils: Suggests uncal herniation, CN III palsy.
Oculocephalic Reflex (Doll’s Eye Test - CN III, IV, VI, VIII):
• Present: Intact brainstem.
• Absent: Brainstem dysfunction.
Corneal Reflex (CN V, VII):
• Absent corneal reflex: Suggests pontine dysfunction.
Gag Reflex (CN IX, X):
• Absent: Brainstem dysfunction (medulla involvement).

Decorticate posturing such as arms flexed and adducted, legs extended with plantar flexion indicates lesion above red nucleus.
Decerebrate posturing such as arms extended and pronated, legs extended with plantar flexion indicates lesion in midbrain

Question 6

Laboratory, imaging and neurophysiological exam in comatose?

Answer 6

Laboratory evaluation is crucial for metabolic causes of coma and should be performed in all cases without clear structural abnormalities.
Essential blood work such : CBC, serum electrolytes, renal function test, liver function test, lactate etc.

If focal neurological signs are present, imaging is required to identify a possible structural lesion. Brain CT scan is first line, MRI is second line for specific cases.

Lumbar puncture if CNS infection is suspected.

EEG can be performed.