This cross-sectional study investigated medical decision-making capacity (MDC) as measured by a standardized psychometric instrument in patients with acute TBI across a range of injury severity. Our present study results demonstrate that impairment of MDC is prevalent in acute TBI and is strongly related to injury severity. Specifically, 1 month after injury, MDC was largely intact for our mTBI group compared to controls, but significantly impaired for both cmTBI and msevTBI groups.
As noted, mTBI patients performed equivalently to controls on all 5 consent standards. This finding suggests that 1 month following injury, consent capacity has returned to normal levels for many patients with mTBI, assuming initial impairment after injury. This finding reflects the broader neuropsychological literature on cognitive recovery in patients with mTBI, which has shown that mTBI patients as a group perform equivalently with controls on most cognitive testing shortly after injury.18–21
At the same time, our study showed some heterogeneity in the MDC of mTBI patients in the acute injury period. Specifically, our categorical impairment ratings showed individual variability in the capacity performance of mTBI patients. Approximately 30% of mTBI patients demonstrated capacity compromise (combined mild/moderate and severe impairment ratings) on appreciation, and another 20% showed compromise on understanding. These capacity ratings thus captured MDC impairment in some individuals with mTBI that were otherwise obscured by group mean scores. There appear to be a subset of individuals with mTBI in this study who continue to have impaired consent abilities a month or more following their injury. It should be noted that multiple studies have shown similar individual heterogeneity in recovery of cognitive abilities over time in mTBI, with a subset of patients demonstrating cognitive impairments a month or longer after their injury.22–24
Such persisting impairment may relate to a number of factors, including age, education, gender, medical issues, premorbid psychiatric status, substance abuse history, and premorbid cognitive status.25–27
In contrast to mTBI, patients with cmTBI 1 month following injury showed impairment on the understanding standard relative to controls. In addition, capacity impairment ratings for this group reflected a different pattern, with nearly half of cmTBI patients showing some level of compromise (mild/moderate or severe ratings) on the 3 complex standards. These findings suggest that structural brain changes found in complicated mild injuries contribute to more significant impairments in decisional capacity that have not resolved a month after injury. This study is thus consistent with literature demonstrating slower recovery rates and worse outcomes in patients with cmTBI compared to patients with uncomplicated mild TBIs.28,29
MDC was most impaired in patients with msevTBI. Relative to the control and mTBI groups, the msevTBI group was impaired on the 3 complex consent standards (S3–S5), and was impaired relative to the cmTBI group on the understanding standard. In addition, the msevTBI group was impaired relative to other groups on the simple standard of expressing choice. Capacity impairment ratings in the msevTBI group showed a similar pattern, with 77% capacity compromise for understanding, 63% for appreciation, and 53% for reasoning, but also 21% for expressing a choice, and 19% for making the reasonable choice.
As previously noted, the msevTBI results replicated and cross-validated results from a previous study investigating MDC in a different sample of msevTBI patients.1
In addition, the present study extended earlier findings by showing msevTBI group impairment on simple consent standards as well (S1 and [S2]). It is likely that the larger msevTBI patient sample in the present study resulted in greater power to detect differences on these elementary standards. In addition, the current sample was likely more severely injured and cognitively impaired than the earlier sample, as evidenced by lower GOAT and GCS scores.
An interesting aspect of the present study was the opportunity to compare the decisional capacity of participants with mTBI vs cmTBI. Across the board, the raw scores of cmTBI patients fell below patients with mTBI on the different CCTI standards. However, the group differences did not reach significance, in substantial part due to the cmTBI group's small sample size and large standard deviations. We anticipate that CCTI score mean differences between the 2 mild groups will reach significance with larger sample sizes.
With respect to individual capacity impairment ratings, however, the 2 mild TBI groups showed clear separation. For example, on appreciation, capacity compromise for cmTBI patients was 47% vs 29% for mTBI patients, a difference of 18%. On understanding, capacity compromise was 47% for cmTBI patients vs 18% for mTBI patients, a difference of 29%. The greatest differential emerged on reasoning, where capacity compromise was 47% for cmTBI but only 7% for mTBI, a difference of 40%. Thus despite having very similar GCS and GOAT scores, mTBI and cmTBI groups had distinctly different capacity impairment rating profiles at 1 month postinjury. This finding highlights the importance of injury severity in understanding initial impairment of decisional capacity in TBI.
The findings also raise questions about how mTBI is defined. In our study, mTBI and cmTBI group were distinguished using conventional cranial CT and MRI scan findings. It is possible that some of the 30% of mTBI cases with impaired capacity ratings in our study might have met criteria for cmTBI if different neuroimaging studies had been performed. For example, recent studies using CT and MRI perfusion, MRS, and DTI show abnormalities in mTBI patients who have no abnormalities on conventional imaging.30–33
Other markers such as reaction time, eye tracking, dynamic balance, and vestibular function may also distinguish mTBI and cmTBI.34
Our finding that one-third of the patients with mTBI had compromised capacity ratings suggests that MDC in TBI must be carefully considered in all patients, including mTBI patients with normal findings on conventional neuroimaging. Approaches in clinic to ensure adequate capacity to consent can include using multiple modalities to convey treatment information (i.e., both auditory and visual), having the patient with TBI explain treatment information presented to them, or administering formal capacity measures like the CCTI.
There were several limitations to the study. First, our sample of cmTBI cases was relatively small and underpowered to find differences between mTBI and cmTBI groups. Second, the impairment ratings were used experimentally for scientific purposes and are not representative of participants' actual legal or clinical competency status. Third, individuals may respond differently to a hypothetical vignette than to real-life, personal medical situations. For example, real-life medical problems may trigger emotional aspects of MDC not captured by hypothetical vignettes. Finally, while our study population was comparable to other TBI patient populations, participants who agree to be in research studies may not completely reflect the general population. Cross-validation of findings in other mild, complicated mild, and moderate/severe TBI patient samples would further establish external validity of the study findings.