Traumatic Brain Injury
Appendix C: Cognitive and Behavioral Changes After TBI
Cognitive complaints are common after concussion/TBI. However, assessing neurocognitive status after injury is problematic as an individual’s prior level of function is an overwhelming driver of post-injury performance on most neuropsychological testing.*1(FMCSA) Performance also declines as subjects’ age,30 making it difficult to compare results in younger and older workers of the same workforce. Other common co-existing diagnoses after TBI, such as depression and PTSD, have been shown to affect performance on cognitive testing.31,32 Of note, in the United States, educational attainment, income, socioeconomic status, native language and job classification (and to a lesser effect age and gender) are all interdependent variables therefore, it is an oversimplification to attribute cognitive performance or decline to only one of the above variables when interpreting results.
It is also important to recognize that an individual may test in the population-based “normal” range while still reporting substantial cognitive decline from their pre-injury perceived level of function. They may test “normal” but have behavioral changes that interfere with performing essential job functions. In the absence of pre-injury data, one commonly used definition of cognitive impairment is test performance at the 5th percentile (1.5 STD below the mean). While this may not be an absolute disqualification for an individual to be able to perform their essential job functions, further investigation is warranted before allowing the individual back to unrestricted duty.
New behavioral symptoms after TBI, such as irritability, temper, and anxiety may be more problematic than cognitive decline in the individual’s ability to perform their essential job functions. Dikmen et al., followed 732 TBI patients (63% of the cohort was diagnosed with mild TBI) and assessed symptoms at 1 month and at 1 year.33 At 1 year, roughly 1/3 of patients endorsed symptoms of anxiety, temper and/or irritability. Of note, the percent of patients with these symptoms was similar for mild, moderate and severe TBI diagnoses. While these behaviors can be identified as part of the neuropsychological evaluation, it is up to the employer to determine if these behaviors interfere with the individual’s ability to perform their job functions efficiently, effectively and to the employer’s satisfaction.
*One of the best examples demonstrating the importance of pre-injury cognitive status on post-injury cognitive testing comes from the Vietnam Penetrating Head Injury study.34 The researchers compared Armed Forces Qualification Test (AFQT) results at time of enlistment and 30 years post-injury to assess cognitive function (Note: the correlation between the AFQT and the WAIS-III Full-Scale IQ score in this population was r = >0.8). In a stepwise regression model to examine change in AFQT score over time, pre-injury AFQT accounted for 51% of the variance, with the next variable (caudate involvement) accounting for only 8.2% of the variance.