The impact of mild traumatic brain injury on cognitive functioning following co-occurring spinal cord injury

Meta-analytic studies have shown that mild traumatic brain injury (MTBI) has relatively negligible effects on cognitive functioning at 90 or more days post-injury. Few studies have prospectively examined the effects of MTBI in acute physical trauma populations. This prospective, cohort study compared the cognitive performance of persons who sustained a spinal cord injury (SCI) and a co-occurring MTBI (N = 53) to persons who sustained an SCI alone (N = 64) between 26 and 76 days (mean = 46) post-injury. The presence of MTBI was determined based on acute medical record review using a standardized algorithm. Primary outcome measures were seven neuropsychological tests that evaluated visual, verbal, and working memory, perceptual reasoning, and processing speed that controlled for potential upper extremity impairment. Persons who sustained SCI with or without MTBI had lower than expected performance across all neuropsychological tests, on average about 1 SD below the mean. Analysis of covariance indicated that persons with MTBI did not evidence greater impairment on any neuropsychological test. The aggregated effect size (Cohen's d) was -0.16. The strongest predictors of neuropsychological test scores were education, race, history of learning problems, and days from injury to rehabilitation admission. MTBI did not predict performance on any neuropsychological test. These findings are consistent with other controlled studies that indicate a single MTBI has negligible long-term impacts on cognition.