Early Prediction of Long-Term Outcome After Traumatic Spinal Cord Injury
Abstract & Commentary
By John J. Caronna, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Caronna reports no financial relationships relevant to this field of study.
Synopsis: A composite score that combines age, motor power, and light touch perception can predict recovery of walking with great accuracy in patients with traumatic spinal cord injury.
Source: van Middendorp JJ, et al. A clinical prediction rule for ambulation outcomes after traumatic spinal cord injury: A longitudinal cohort study. Lancet 2011;377:1004-1010.
A precise knowledge of the prognosis for recovery of walking after traumatic spinal cord injury (TSCI) is of extreme importance, not only to the injured individual but also to the treating physician, who must consider acute surgical and pharmacologic interventions, and afterwards, set realistic goals for rehabilitation. To satisfy this clinical need, van Middendorp and associates propose a clinical prediction rule to assess a patient's chances of walking independently after TSCI. The rule was derived from the American Spinal Injury Association/International Spinal Cord Society Neurological Standard Scale.1
The study population comprised 1442 adults with TSCI admitted to 19 European centers between 2001 and 2008. Because no proven effective treatment of TSCI is available, no attempt was made to standardize or record the details of the treatments applied and the focus or intensity of the rehabilitation programs prescribed.
Enrolled patients underwent early (< 15 days) and late (1-year follow up) clinical examinations. Of these, 492 had available outcome measures. The ability to walk independently 1 year after injury was the primary functional outcome. Six-month follow-up measurements were used for patients without 1-year follow-up examination. Spinal cord independence measures2 were assessed by physicians, physiotherapists, and occupational therapists.
The variables showing excellent discrimination between independent walkers and dependent or non-walkers were: age (< 65 vs > 65 years), motor scores of the quadriceps femoris (L3, L4) and gastrocsoleus (S1) muscles, and light touch sensation of dermatomes L3 and S1. The performance of the clinical prediction rule was validated in an additional 389 adults with TSC1 admitted between 2008 and 2009. The probability that an individual would be able to walk at 1 year after TSCI was estimated using the weighted coefficients of the final prediction rule (see Table) with a minimum total score of -10 and a maximum total score of 40.
The authors calculated the probability and 95% confidence interval of walking independently at 1 year, based on the prediction rule score: A score of -10 predicts no chance of independent ambulation. At a score of 10, the probability is approximately 35%, at 15 it is about 77%, at 20 it is almost 90%, and at a score of 30 or above, the probability is 100%.
Prior to the widespread recognition of the value of multivariate prognostic models to determine functional outcome after traumatic brain injury or following medical (non-traumatic) coma, physicians often based early prognostications on a single neurological sign. In the case of coma, the most common predictor was the presence or absence of the pupillary light reflex. In spinal cord injury, the predictor usually chosen was the presence or absence of anal sensation.
The authors have used logistic regression analysis to develop a simple clinical prediction rule to calculate the probability of a patient being able to walk independently at 1 year after TSCI. On the basis of age and four clinical neurologic tests, the probability of walking can be calculated more easily and probably more accurately than with the grading systems in use at present. The authors, however, have not provided detailed information about the quality of walking in their good outcome patients. Such information is necessary to determine whether a novel treatment strategy results in a better than predicted, that is, improved outcome in patients with prediction rule scores in the intermediate range of 10 to 20.
Other investigators will no doubt also wish to determine whether the combined use of the prediction rule with somatosensory evoked potentials improves prognostic accuracy. Nevertheless, the authors have provided clinicians with a validated, simple, clinical prediction rule that can be used to counsel TSCI patients and their families during the initial phase after injury.
1. American Spinal Injury Association. International standards for neurological classification of spinal cord injury, revised 2002. Chicago IL: Amer Spinal Injury Assoc; 2002.
2. Catz A, et al. A multicenter international study on the Spinal Cord Independence Measure, version III: Rasch psychometric validation. Spinal Cord 2007;45:275-291.