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    An Update of the ASIA/ISCOS SCI Classification System

    AN UPDATE OF THE ASIA/ISCOS SCI CLASSIFICATION SYSTEM
    Wise Young PhD MD
    11 January 2012

    KLD (SCI-Nurse) requested an update of the American Spinal Injury Association (ASIA) and International Spinal Cord Society (ISCOS) spinal cord injury classification and neurological scoring system. This classification system began in the 1970’s. In 1990, ASIA significantly revised this classification and ISCOS adopt the new standard [1]. The standard was revised in 2000 [3] and then more recently in 2010. The following is a summary of the changes in the Fourth, Fifth, and Sixth Editions of the ASIA/ISCOS Spinal Cord Injury Classification System.

    The Fourth Edition of the ASIA/ISCOS Classification (1990)
    For many years, ASIA used a spinal cord injury classification system that is a modification of one that was developed by Hans Frankel in the 1970’s. The Frankel classification system used a series of letters (A, B, C, D, and E) to signify complete, sensory incomplete, motor incomplete (not useful), motor incomplete (useful), and normal. In 1990, ASIA significantly revised this system, as described below.

    I. ASIA Impairment Scale (AIS)
    • A. "Complete" Spinal Cord Injury, defined by absence of anal sensation and voluntary anal contraction.
    • B. "Sensory Incomplete" Spinal Cord Injury, defined by presence of anal sensation. Other preserved sensation may be present below the injury level.
    • C. "Motor Incomplete" Spinal Cord Injury, defined by presence of anal sensation or voluntary sphincter contraction and some voluntary motor activity that is less than 50% of the summed motor score below the injury level.
    • D. "Motor Incomplete" Spinal Cord Injury, defined by the presence of anal sensation or voluntary anal sphincter contraction and motor activity that is greater than or equal to 50% of the motor score below the injury level.
    • E. "Normal" Spinal Cord Injury, defined by normal motor and sensory scores, as well as anal sensation and sphincter contraction.

    II. Neurological level.
    • The sensory level is the lowest contiguous dermatome that has normal pinprick and touch sensation on both sides.
    • The motor level is the lowest contiguous segment that has "intact" motor scores (≥3) on both sides and the next higher segment has normal (5) muscle strength scores.
    • If the sensory level is in the thoracic region, the neurologic level is signified by the lowest contiguous sensory dermatome on both sides.
    • A single neurological level is one in which the lowest contiguous spinal segment that has intact motor and normal sensory scores.
    • A zone of partial preservation was defined as the number of segments that had partial loss of motor and sensory function.

    III. Motor and Sensory Scores
    • Motor Score. Ten muscles are scored on a scale of 0-5, where 0 is no movement, 1 is slight movement, 2 is movement but not against gravity, 3 is movement against gravity, 4 is movement against moderate resistance, and 5 is normal. Ten key muscles were used: elbow flexors (C5), wrist extensor (C6), elbow extensors (C7), finger flexors (C8), finger abductors (T1), hip flexors (L2), knee extensors (L3), ankle dorsiflexors (L4), long toe extensors (L5), ankle plantar flexors (S1). The scores are summed on each side of the body for a total of 100 points.
    • Pinprick Sensation. The left and right dermatomes from C2 through S4/5 are scored on a scale of 0-2 for painful sensation to pinprick, where 0 is absent, 1 is abnormal, and 2 is normal. This is tested with a sharp pin applied to defined points close to the center of each dermatome. The scores from both sides re summed for a normal total of 112 points.
    • Touch Sensation. Each left and right dermatomes from C2 through S4/5 are scored on a scale of 0-2 for light touch, where 0 is absent, 1 is abnromal, and 2 is normal. This is tested with a cotton wisp applied applied to defined points close to the center of each dermatome. The scores from both sides re summed for a normal total of 112 points.

    IV. Syndromes. The 1992 Classification system also defined spinal cord injury syndromes, including central cord syndrome, Brown-Séquard syndrome, anterior spinal cord syndrome, conus medullaris syndrome, and cauda equina syndrome.

    The Fifth Edition of the ASIA/ISCOS Classification (2000)

    In 2000, the following changes were made in the ASIA Classification:

    I. ASIA Impairment Scale (AIS)
    • A. Complete. In addition to the voluntary anal contraction (VAC) and S4/5 pinprick and touch sensation, the examiner now notes presence of anal sensation (Y/N) during the anal examination and absence was required for classifying the injury as AIS A.
    • B. Incomplete.* "Sensory but not motor function is preserved below the neurological level or includes the sacral segments C4/S5".
    • C. Incomplete.* "Motor function is preserved below the neurological level, and more than half of key muscles below the neurological level have a muscle grade less than 3 (Grade 0-2)."
    • D. Incomplete.* "Motor function is preserved below the neurological level, and at least half of key muscles below the neurological level have a muscle grade greter than or equal to 3."
    • E. Normal.
    * For an individual to receive a grade of C or D, the individual must have sensory or motor function in the sacral segments S4/5. In addition, the individual must have either (1) voluntary anal sphincter contraction or (2) sparing of motor function more than three levels below the motor level.

    II. Neurological Level.
    • Motor level. The 2002 and 2006 booklet contains a discussion which points out "By convention, if a muscle has at least a grade of 3, it is considered to have intact innervation by the more rostrl of the innervating segments. In determining the motor level, the next most rostral segment must test as a 5, since it is assumed that the muscle will have both of its two innervating segments intact. For example, if no activity is found in the C7 key muscle and the C6 muscle is graded as 3, then the motor level for the tested side of the body is C6, providing that the C5 muscle is graded 5."
    • The Standard provided several steps in the classification.
    1. Determine sensory levels on the right and left sides.
    2. Determine motor levels for the right and left sides. “In regions where there is no myotome to test, the motor level is presumed to be the same as the sensory level, if testable motor function above that level is also normal”.
    3. Determine the single neurological level. “This is the lowest segment where motor and sensory function is normal on both sides, and is the most cephalad of the sensory and motor levels determined in steps 1 and 2.
    4. Determine whether the injury is Complete or Incomplete, i.e. presence or absence of sacral sparing. If voluntary anal contraction (VAC) is No, all S4-S5 sensory scores are 0, and deep anal pressure (DAP) is No, then the injury is complete.
    5. Determine ASIA Impairment Scale.
    a. Is the injury complete. If yes, AIS = A.
    b. Is the injury motor incomplete. If no, AIS = B.
    c. AIS = C or D if voluntary anal contraction is present or greater than three levels of motor function is present if the patient is sensory incomplete.
    d. If at least half o the key muscles below the injury site are 3 or better, then AIS = D, otherwise AIS = C.
    e. If all motor and sensory scores are normal, AIS = E.

    III. Motor and Sensory Scores
    • Sensory scores. In addition to the previous definitions, the notation "NT" was introduced representing "not testable".
    • Motor scores. The strength of each muscle is graded on a six-point scale. In addition from the usual 0-5, there is now a 5* indicating "normal active movement, full ROM against sufficient resistance to be considered normal if identified inhibiting factors were not present". Such inhibiting factors include pain and atrophy.

    The Sixth Edition of the ASIA Classification (2010)

    In 2010, the following revisions were made to the ASIA/ISCOS Classification

    I. ASIA Impairment Scale (AIS).
    • A. Complete. This category of "Complete" spinal cord injury is similar to previous definitions except that the term "Deep Anal Pressure" was substituted for "Any anal sensation". Sacral sensation is now defined as light touch and pinprick at S4-S5, or deep anal pressure (DAP).
    • B. Sensory Incomplete. The criterion of “no motor function is preserved more than three levels below the motor level on either side of the body" was added to the definition.
    • C. Motor Incomplete. This category differs from previous versions in two respects. First, the name is “Motor Incomplete” instead of “Incomplete”. Second, the definition is “more than half of key muscle functions below the single neurological level of injury (NLI) have a muscle grade of less than 3 (Grades 0-2)”. A footnote indicates that “The Standards at this time allows even non-key muscle functions more than 3 levels below the motor level to be used in determining motor incomplete status (AIS B vs. C).” A footnote indicates that a classification of C requires voluntary anal contraction or “sacral sensory sparing with sparing of motor function more than three levels below the motor level for that side of the body.”
    • D. Motor Incomplete. The definition of D differs from previous ones in three respects. First, instead of just "Incomplete", the category is named “Motor Incomplete”. Second, the definition includes the term NLI (single neurological level). Third, similar to category C, the definition requires voluntary anal contraction or sparing of motor function more than three levels below the motor level for that side of the body.
    • E. Normal. The definition of E was expanded to include “the patient had prior deficits” and “someone without an initial SCI does not receive an AIS grade”.

    II. Neurological Level.
    The definition of neurological level remains essentially similar to previous years.

    III. Neurological Scores.
    The motor and sensory scores are essentially the same as the Fifth Edition (2000).

    Discussion

    While the differences between the fourth (1990), fifth (2000), and sixth (2010) versions of the ASIA Classification appear to be small and possibly trivial, four changes may alter the classification and levels of people with spinal cord injury.

    First, the addition of “any anal sensation (Y/N)” in 2000 and then its replacement by “deep anal pressure (Y/N)” in 2010 may have initially increased the number of incomplete patients and then reduced the number compared to the 1990 Classification which stipulated simply the presence of S4/5 sensation or voluntary anal contraction. Many patients may retain some anal sensation but no peri-anal sensation ta S4-S5 and no anal voluntary anal sphincter contraction. Such people may have been classified as AIS A before but now would be classified as AIS B if they have no motor preservation more than 3 levels below the injury site and AIS C or D if they have some motor preservation more than 3 levels below injury site. This should increase the number of patients classified as "incomplete".

    Second, the additional criterion of motor activity 3 levels below the injury site for AIS C & D clarified the definition of motor incomplete. Although the fourth edition (1990) did not specify that patients must have voluntary anal sphincter contraction before they could be categorized as AIS C or D, some examiners may have assumed that this was true and classified patients as AIS B if they did not have anal sphincter function. This placed too much weight on preservation of anal sphincter contraction. In addition, presence of non-key muscle activity more than 3 levels below the injury site would also count as motor preservation. For example, Christopher Reeve recovered ability to move his left index finger at 3-4 years after injury. He had anal sensation but no anal voluntary sphincter contraction. he would have been classified as ASiA B under the Fourth Edition (1990) but would have been classified as ASIA C from 2000 on.

    Third, the assignment of AIS E now requires previous deficits. This avoids assignment of the ASIA classification to people who had no motor or sensory loss at any time after injury. In other words, this criterion limits the AIS E categorization to people who are recovering from some loss of motor and sensory scores. If a patient is classified as AIS E, the classification implies that the person did have transient loss of pinprick, light touch, and key muscle motor function for some time after injury.

    Finally, starting in 2000, the ASIA classification included a motor score of 5*. This score is applied when the examiner believes that the muscle is functioning with strength that is normal for an abnormal situation, including presence of pain or atrophy, that may limit the ability of the patient to exert full strength. In other words, the ASIA Classification is about spinal cord injury and not about other causes of muscle weakness. All editions of the ASIA/ISCOS Classification defined the motor level as most caudal contiguous "normal" segment on both sides. The term normal indicates "intact" motor innervation of a segment if the key muscle representing the segment has a score that is equal or greater than 3 and the adjacent cephalad (towards the head) segment has a score of 5. For example, if a person has a motor score of 5* in C5 (elbow flexors) and a motor score of 3 for C6 (wrist extensors) on both sides, and normal sensation in C6, that person has a neurological level of C6.

    In summary, the fourth version (1990) of the ASIA Classification introduced three major changes in the ASIA classification system by defining AIS A as absence of sacral sparing, stipulating that the neurological level is the lowest contiguous "intact" level on both sides, and quantifying the dividing line between AIS C and D as greater than or equal to 50% of the motor score. The fifth version (2000) clarified the classification by adding the criterion of "Any anal sensation" for sacral sparing, stipulating that presence of voluntary anal contraction or motor activity more than 3 levels below the injury site would allow the designation of AIS C or D, and adding a new motor score of 5* to indicate normal muscle innervation in situation that may limit expression of muscle power. The sixth version (2010) replaced the criterion of "Any anal sensation" with "Deep anal pressure", required that AIS E can be only applied if there had been previous neurological deficits, and specified that motor activity of any non-key muscle more than 3 levels below the injury site would be sufficient for AIS C or D.


    References

    1. Ditunno JFJ, Young W, Donovan WH, Bracken MB, Brown M, Creasey G, Ducker TB, Maynard FMJ, Stover SS, Tator CH, Waters RL and Wilberger JE (1992). Standards for Neurological Classification of Spinal Cord Injury. American Spinal Injury Association, Chicago. 25 pages.

    2. Marino RJ, Barros T, Biering-Sorensen F, Burns SP, Donovan WH, Graves DE, Haak M, Hudson LM and Priebe MM (2003). International standards for neurological classification of spinal cord injury. J Spinal Cord Med 26 Suppl 1: S50-6.
    Last edited by Wise Young; 01-12-2012 at 12:58 AM.

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