Spinal Shock: Primary Cause
Spinal shock is caused by the sudden disruption of spinal cord function following traumatic injury, resulting in temporary loss or depression of all spinal reflex activity below the level of injury. 1
Pathophysiological Mechanism
The primary cause is an immediate traumatic insult to the spinal cord that triggers a cascade of events:
- Mechanical damage to neuronal and glial cell membranes occurs at the moment of impact 2
- Disruption of the microvasculature leads to hemorrhage and blood-spinal cord barrier breakdown 2
- Ionic dysregulation develops, with recent evidence showing massive chloride ion dysregulation occurring within 200 milliseconds of injury 3
- Immediate spreading depolarization propagates from the injury site throughout the spinal cord with distinct segmental velocities 3
Clinical Manifestations
The physiologic or anatomic transection results in:
- Complete loss of spinal reflex activity below the injury level 1
- Hypotension and bradycardia (neurogenic shock) when cervical or high thoracic injuries cause loss of sympathetic tone 2
- Respiratory failure in cervical and high thoracic injuries due to loss of respiratory muscle innervation 2
Critical Distinction
Only 19.3% of cervical cord injuries present with classic neurogenic shock (hypotension + bradycardia) upon emergency department arrival 4. This is far lower than traditionally taught, with thoracic injuries showing only 7% and lumbar injuries 3% incidence 4.
Secondary Injury Cascade
The initial trauma immediately initiates secondary injury mechanisms that compound the damage:
- Loss of cardiovascular sympathetic innervation leads to profound hypotension, further compounding ischemic insult to the cord 2
- Immune paralysis develops from loss of sympathetic innervation to lymphatic organs, increasing infection susceptibility 2
- Proapoptotic signaling and ongoing cellular death extend beyond the initial mechanical injury 2
Duration and Recovery
Spinal shock duration varies considerably between patients, lasting from days to up to 12 weeks 5. The end of spinal shock is marked by the return of abnormal cutaneous or muscle spindle reflex arcs below the injury level 1. These returning reflexes are permanently altered and form the basis for rehabilitation efforts 1.
Important Caveat
The mechanism causing spinal shock is usually immediate and traumatic, but can occasionally progress over several hours 1. Reflex arcs immediately above the injury level may also be severely depressed (Schiff-Sherrington phenomenon) 1.