Classification of Spinal Cord Injury Severity
Clinicians have long used a clinical scale to grade severity of neurological loss. First devised at Stokes Manville before World War II and popularized by Frankel in the 1970’s, the original scoring approach segregated patients into five categories, i.e. no function (A), sensory only (B), some sensory and motor preservation (C), useful motor function (D), and normal (E).
The ASIA Impairment Scale, shown by Figure 4 to the right, follows the Frankel scale but differs from the older scale in several important respects. First, instead of no function below the injury level, ASIA A is defined as a person with no motor or sensory function preserved in the sacral segments S4-S5. This definition is clear and unambiguous. ASIA B is essentially identical to Frankel B but adds the requirement of preserved sacral S4-S5 function. It should be noted that ASIA A and B classification depend entirely on a single observation, i.e. the preservation of motor and sensory function of S4-5.
The ASIA scale also added quantitive criteria for C and D. The original Frankel scale asked clinicians to evaluate the usefulness of lower limb function. This not only introduced a subjective element to the scale but also ignored arm and hand function in patients with cervical spinal cord injury. To get around this problem, ASIA stipulated that a patient would be an ASIA C if more than half of the muscles evaluated had a grade of less than 3/5. If not, the person was assigned to ASIA D.
ASIA E is of interest because it implies that somebody can have spinal cord injury without having any neurological deficits at least detectable on a neurological examination of this type. Also the ASIA motor and sensory scoring may not be sensitive to subtle weakness, presence of spasticity, pain, and certain forms of dysesthesia that could be a result of spinal cord injury. Note that such a person would be categorized as an ASIA E.
These changes in the ASIA scale significantly improved the reliability and consistency of the classification. Although it was more logical, the new definition of “complete” injury does not necessarily mean that it better reflects injury severity. For example, is there any situation where a person could be an ASIA B and better off the ASIA C or even ASIA D?
The new ASIA A categorization turns out to be more predictive of prognosis than the previous definition where the presence of function several segments below the injury site but the absence of function below a given level could be interpreted as an “incomplete” spinal cord injury.
The ASIA committee also classified incomplete spinal cord injuries into five types. A central cord syndrome is associated with greater loss of upper limb function compared to the lower limbs. The Brown-Sequard syndrome results from a hemisection lesion of the spinal cord. Anterior cord syndrome occurs when the injury affects the anterior spinal tracts, including the vestibulospinal tract. Conus medullaris and cauda equina syndromes occur with damage to the conus or spinal roots of the cord.
Much confusion surrounds the terminology associated with spinal cord injury levels, severity, and classification. The American Spinal Injury Association tried to sort some of these issues and standardize the language that is used to describe spinal cord injury. The ASIA Spinal Cord Injury Classification approach has now been adopted by almost every major organization associated with spinal cord injury. This has resulted in more consistent terminology being used to describe the findings in spinal cord injury around the world.