Effects of mild traumatic brain injury cannot be differentiated from substance abuse

Patients involved in litigation relating to mild traumatic brain injury (MTBI) typically undergo a forensic neuropsychological evaluation. However, if cognitive problems are identified, it is difficult to know whether these are related to the MTBI or other factors such as pre- and/or post-injury substance abuse. The purpose of this study was to compare the neuropsychological test performances of 73 patients with acute, uncomplicated MTBIs to a sample of 73 patients from an inpatient substance abuse programme.

Patients were perfectly matched on age, education and gender. Ten cognitive measures were used that included the Trail Making Test (TMT) and selected sub-tests from the Wechsler Memory Scale-Revised.

Patients with MTBI demonstrated poorer performances on Digits Backwards (p < 0.028) and TMTA (p < 0.032). There were no significant differences between the two groups on the remaining cognitive measures. The clinical usefulness of these measures to differentiate between the groups, using discriminant function analysis, was very poor.

Patients with uncomplicated MTBIs could not be reliably differentiated from patients with substance abuse problems on these measures of concentration, memory and processing speed.