What are the criteria for a definitive diagnosis of spinal shock in a patient with a suspected spinal cord injury?

Criteria for Definitive Diagnosis of Spinal Shock

Spinal shock is definitively diagnosed by the presence of complete loss or severe depression of all spinal reflex activity below the level of spinal cord injury, with the key diagnostic criterion being absent or severely depressed deep tendon reflexes in the acute phase following cord transection. 1

Core Diagnostic Criteria

The diagnosis of spinal shock requires documentation of the following clinical features occurring immediately after spinal cord injury:

Neurological Findings Below the Injury Level

• Complete loss of deep tendon reflexes is the hallmark finding that defines spinal shock, distinguishing it from other forms of acute spinal cord injury 1
• Flaccid paralysis with complete loss of muscle tone in affected limbs, rather than spasticity 2, 3
• Sensory loss affecting all modalities below the level of injury 2
• Loss of cutaneous reflexes including the bulbocavernosus reflex and anal wink 1

Autonomic Dysfunction (Level-Dependent)

• Neurogenic shock manifesting as hypotension and bradycardia occurs specifically with injuries above T6 due to loss of sympathetic tone 4, 5
• Bladder areflexia with urinary retention 2
• Loss of bowel control and absent rectal tone 2
• Impaired thermoregulation and vasomotor instability 2

Temporal Characteristics

• Spinal shock begins immediately following the traumatic injury or cord transection 1
• Duration is highly variable between patients, ranging from days to up to 12 weeks 2
• Resolution is marked by the return of reflex activity, typically beginning with the bulbocavernosus reflex, though the returning reflexes are pathologically altered and hyperactive 1, 6

Electrophysiological Confirmation

While not required for diagnosis, objective testing can support the clinical diagnosis:

• Low persistence or absence of F-waves during the acute phase 3
• Preserved H-reflexes despite absent tendon reflexes, which helps distinguish spinal shock from peripheral nerve injury 3
• Somatosensory evoked potentials show characteristic changes reflecting the cord injury 2
• Peripheral motor axon excitability studies demonstrate depolarization-like features peaking around days 11-17 post-injury, with "fanned in" threshold electrotonus and reduced superexcitability 7

Critical Diagnostic Pitfalls

• Do not confuse spinal shock with neurogenic shock—spinal shock refers to the neurological phenomenon of reflex loss, while neurogenic shock is the hemodynamic consequence of high cord injuries 4
• Absence of reflexes does not indicate irreversible injury—reflex return signals the end of spinal shock but does not predict functional recovery 1, 6
• The Schiff-Sherrington phenomenon can cause reflex depression one to two segments above the actual injury level, potentially leading to overestimation of injury extent 1
• Autonomic reflexes may return variably and do not follow the same timeline as somatic reflexes 1

Imaging Requirements for Complete Assessment

While spinal shock is a clinical diagnosis, imaging is essential to identify the underlying structural injury:

• CT is the gold standard for identifying vertebral fractures and bony injury with 94-100% sensitivity 8, 5
• MRI is mandatory when neurological deficits are present, as it directly visualizes cord injury, ligamentous disruption, and epidural hematoma that may be invisible on CT 4, 5
• Up to 25% of cervical spine injuries involve purely ligamentous instability without fracture, requiring MRI for diagnosis 4
• Image the entire spine as 20% of patients have noncontiguous injuries at multiple levels 8, 4