What is the approach to a comprehensive Central Nervous System (CNS) examination in a patient presenting with acute symptoms?

Comprehensive Central Nervous System (CNS) Examination in Acute Presentations

Initial Assessment

The most effective approach to a comprehensive CNS examination in patients with acute symptoms begins with a structured neurological assessment using validated scales, followed by targeted imaging based on clinical presentation, with MRI being the preferred modality when available. 1

Level of Consciousness Assessment

• Use the Full Outline of Unresponsiveness (FOUR) score instead of the Glasgow Coma Scale (GCS) in acute settings 2

  • FOUR score better captures subtle changes in consciousness and can be used in intubated patients
  • Components: eye response, motor response, brainstem reflexes, respiration pattern

• Alternative simple scales when rapid assessment is needed:

  • ACDU (Alert, Confused, Drowsy, Unresponsive) - more evenly distributed than AVPU 3
  • AVPU (Alert, responds to Voice, responds to Pain, Unresponsive) 3

Cranial Nerve Examination

• Pupillary response: size, symmetry, and reactivity to light
• Extraocular movements: assess for gaze palsies, nystagmus
• Facial symmetry: assess for facial weakness
• Probe for voluntary eye movements using a mirror 4
• Assess brainstem reflexes (corneal, gag, cough)
• Evaluate for meningeal signs: nuchal rigidity, Kernig's sign, Brudzinski's sign

Motor and Sensory Examination

• Motor strength in all extremities (grade 0-5)
• Muscle tone and assessment for abnormal posturing
• Deep tendon reflexes and plantar responses
• Sensory testing: light touch, pain, temperature, proprioception
• Coordination: finger-to-nose, heel-to-shin, rapid alternating movements

Advanced Assessment Techniques

• Continuous performance test: ask patient to raise hand when hearing a specific letter in a standardized sentence 5
• Three consecutive hand position test: "thumbs up-fist-victory sign" 5
• For patients with altered consciousness, use the Coma Recovery Scale-Revised for repeated assessments in subacute and chronic settings 4

Diagnostic Imaging

• Non-contrast CT head should be completed within 25 minutes for patients eligible for thrombolytic therapy 2

  • Rapidly identifies hemorrhage, large infarcts, mass lesions, hydrocephalus
  • First-line in emergency settings, especially with trauma history 1

• MRI brain (without IV contrast) is superior when available 1

  • Higher sensitivity for detecting focal lesions (70% vs 30% for CT)
  • Better for detailed evaluation of brain parenchyma
  • Consider tailored protocols with shorter scan times for agitated patients 2

Laboratory and Additional Testing

• Lumbar puncture when CNS infection is suspected 2

  • Perform after imaging if increased ICP is suspected
  • CSF analysis: cell counts, glucose, protein, Gram stain, culture
  • If bacterial meningitis is suspected and LP is delayed, start empirical antibiotics after blood cultures 2

• EEG is important but typically performed after brain imaging 1

  • Search for sleep patterns, particularly REM and slow-wave sleep 4
  • Consider standard clinical EEG to complement behavioral assessment 4

Special Considerations

• Patients on anticoagulants: Higher risk for intracranial bleeding; prioritize immediate head CT 2

• Febrile patients: Consider CNS infection; lower threshold for lumbar puncture 2

  • Risk factors for abnormal brain imaging in febrile elderly with AMS: lower GCS, lateralizing signs, higher systolic BP, lower body temperature 2

• Patients with focal neurological deficits: Require urgent neuroimaging to rule out stroke, hemorrhage, or space-occupying lesions 2

• Positioning: Individualize head of bed position; traditionally 25-30° elevation if increased ICP is suspected 2

Common Pitfalls and Caveats

1. Relying solely on GCS in intubated patients: Use FOUR score or other scales that don't require verbal response 4

2. Delaying treatment for imaging: If bacterial meningitis is suspected and lumbar puncture is delayed, start empirical antibiotics after blood cultures 2, 6

3. Missing subtle changes in consciousness: Up to 34% of patients with normal neurological examination may have focal lesions on CT 1

4. Overlooking non-neurological causes: Up to 50% of CNS dysfunction may be due to systemic medical conditions 7

5. Inadequate follow-up assessment: Repeat clinical assessments in subacute settings using standardized tools 4

Remember that the yield of neuroimaging in altered mental status is relatively low (11% in one meta-analysis), but critical findings that change management make it essential in the acute setting 2.