Scoring the Motor Component of GCS in Bilateral Paralysis
In patients with bilateral paralysis, score the motor component of the GCS as M1 (no motor response), because true paralysis prevents any voluntary or reflexive motor response to stimulation, regardless of the patient's underlying level of consciousness. 1
Understanding the Critical Distinction
The motor component is the most robust element of the GCS and maintains predictive value even when other components cannot be assessed. 2, 1 However, bilateral paralysis creates a unique challenge because it mechanically prevents any motor response, making it impossible to assess cortical function through movement. 3
Key Assessment Principles
Use central painful stimuli (supraorbital pressure or trapezius squeeze) rather than peripheral stimuli to avoid confusing spinal reflexes with cortical responses. 1 This distinction becomes critical when attempting to differentiate true paralysis from cortical dysfunction.
Document confounding factors explicitly. Before assigning M1, you must exclude or document major confounders including sedation, neuromuscular blockade, hypothermia, severe hypotension, hypoglycemia, and metabolic derangements. 2 These factors can mimic paralysis and must be reversed or accounted for before definitive assessment.
Suspend sedatives and neuromuscular blocking drugs for sufficient time to avoid interference with clinical examination, using antidotes when residual effects are suspected. 2 Short-acting agents are preferred to facilitate accurate neurological assessment.
The Motor Scoring Hierarchy (for reference)
- M6 = Obeys commands 1
- M5 = Localizes to pain (purposeful movement crossing midline) 1
- M4 = Withdraws from pain 1
- M3 = Abnormal flexion (decorticate posturing) 1
- M2 = Abnormal extension (decerebrate posturing) 1
- M1 = No motor response 1
Critical Clinical Pitfall
Do not confuse bilateral paralysis with bilateral absence of motor response from severe brain injury. The distinction matters for prognostication: 2
- In post-cardiac arrest patients treated with therapeutic hypothermia, a GCS motor score ≤2 at day 3 is considered an unreliable prognosticator of poor outcome. 2
- Conversely, a motor score >3 on day 4 predicts favorable outcome with 84% specificity and 77% sensitivity. 1
If the paralysis is from a known spinal cord injury, neuromuscular disease, or iatrogenic paralysis (e.g., ongoing neuromuscular blockade for ventilator management), document this explicitly as "M1 secondary to [specific cause]" to avoid misinterpretation regarding brain function. 2
When Prolonged Paralysis Prevents Assessment
When prolonged sedation or paralysis is medically necessary (e.g., severe respiratory insufficiency requiring deep sedation and paralysis), postpone prognostication until reliable clinical examination can be performed. 2 In these situations, consider alternative modalities that are insensitive to drug interference:
- Somatosensory evoked potentials (SSEPs) - bilateral absence of N20 wave at ≥24 hours post-injury predicts poor outcome with high specificity. 2
- Pupillary and corneal reflexes - maintain prognostic value regardless of paralysis. 2
- Biomarkers and imaging studies - can provide prognostic information when motor examination is unreliable. 2
Documentation Requirements
Always record individual component scores (E, V, M) rather than just the sum, as patients with identical total scores but different component profiles have vastly different outcomes. 1 For a paralyzed patient, document as "E[score]V[score]M1 - bilateral paralysis due to [cause]" to provide complete clinical context.