Excerpt from Spinal Cord Injury: Definition, Epidemiology, Pathophysiology


Synonyms, Key Words, and Related Terms: Brown-Séquard syndrome, central cord syndrome, anterior cord syndrome, conus medullaris syndrome, cauda equina syndrome

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Spinal cord injury (SCI) is an insult to the spinal cord resulting in a change, either temporary or permanent, in its normal motor, sensory, or autonomic function. The International Standards for Neurological and Functional Classification of Spinal Cord Injury is a widely accepted system describing the level and the extent of injury based on a systematic motor and sensory examination of neurologic function. The following terminology has developed around classification of SCI:

  • Tetraplegia (replaced the term quadriplegia) - Injury to the spinal cord in the cervical region with associated loss of muscle strength in all 4 extremities

  • Paraplegia - Injury in the spinal cord in the thoracic, lumbar, or sacral segments, including the cauda equina and conus medullaris

SCI can be sustained through different mechanisms with the following 3 common abnormalities leading to tissue damage:

  • Destruction from direct trauma

  • Compression by bone fragments, hematoma, or disk material

  • Ischemia from damage or impingement on the spinal arteries

Edema could ensue subsequent to any of these types of damage. The different clinical presentations of the above causes of tissue damage are explained further below.

Spinal shock

Spinal shock is a state of transient physiological (rather than anatomical) reflex depression of cord function below the level of injury with associated loss of all sensorimotor functions. An initial increase in blood pressure is noted due to the release of catecholamines, followed by hypotension. Flaccid paralysis, including of the bowel and bladder, is observed, and sometimes sustained priapism develops. These symptoms tend to last several hours to days until the reflex arcs below the level of the injury begin to function again (eg, bulbocavernosus reflex, muscle stretch reflex [MSR]).

Neurogenic shock

Neurogenic shock is manifested by the triad of hypotension, bradycardia, and hypothermia. Shock tends to occur more commonly in injuries above T6, secondary to the disruption of the sympathetic outflow from T1-L2 and to unopposed vagal tone, leading to decrease in vascular resistance with associated vascular dilatation. Neurogenic shock needs to be differentiated from spinal and hypovolemic shock. Hypovolemic shock tends to be associated with tachycardia.

Autonomic dysreflexia

See the article Autonomic Dysreflexia. In a recent study showing high incidence of autonomic dysfunction, including orthostatic hypotension and impaired cardiovascular control, assessment of autonomic function was recommended as a routine along with American Spinal Injury Association (ASIA) assessment.

Motor strengths and sensory testing

The extent of injury is defined by the ASIA Impairment Scale (modified from the Frankel classification), using the following categories:

  • A - Complete: No sensory or motor function is preserved in sacral segments S4-S5.

  • B - Incomplete: Sensory, but not motor, function is preserved below the neurologic level and extends through sacral segments S4-S5.

  • C - Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have muscle grade less than 3.

  • D - Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have muscle grade greater than or equal to 3.

  • E - Normal: Sensory and motor functions are normal.

Perform rectal examination to check motor function or sensation at the anal mucocutaneous junction. The presence of either is considered sacral-sparing.

Definitions of complete and incomplete SCI are based on the above ASIA definition with sacral-sparing.