In the present study, we describe potential effects of the relationships between demographics, injury variables, medical comorbidities, and pre-injury psychiatric conditions on NPDs experienced by TBI patients. Using a matched cohort we first determined the increased risk of NPDs in those with and without TBI. Then, we established that TBI is a heterogenous population demonstrating distinct clinical profiles (phenotypes), that show significant differences in the development of NPDs, suggesting their potential utility in risk stratification. This study is a proof-of-concept and further research is needed to assess the utility of these phenotypes to guide clinical management of TBI patients.
Previous research indicates that TBI patients are at greater risk for developing NPDs with rates ranging from 18.3–60.8% in the first year post-injury [24, 25]. Our results are consistent with these findings as the rates of NPD-A and NPD-P at two years in the current study were 36–47%. Results from a regression model in the matched cohort revealed that in the cohort without pre-injury psychiatric conditions, the odds of developing NPD were 2.8 times greater in those with TBI. In the cohort with pre-injury psychiatric conditions, those with TBI had 2.4 greater odds for developing NPD compared to controls. Thus, head injury alone and in combination with pre-injury psychiatric conditions appears to contribute to increased risk of post-injury psychiatric disorders compared to controls. A previous population-based study demonstrated an increase in risk for all psychiatric outcomes after head injury in patients without pre-injury psychiatric history [26]. Prior studies also support the finding that among TBI patients, pre-injury disorders are significant predictors of post-injury disorders [11, 27]. We speculate that there are several justifications for how TBI may act independently and in conjunction with pre-injury psychiatric disorders to increase the risk of NPDs. TBI induces neurochemical imbalances, neuroinflammation, and disruptions in neural circuits, which are all known to contribute to the emergence of psychiatric symptoms [28]. Furthermore, even in the absence of pre-injury psychiatric conditions, the psychological and physiological stress triggered by injury may lead to the development of NPDs. Among individuals with pre-injury psychiatric conditions, the alteration in the brain's resilience and adaptive mechanisms, make it more vulnerable to the neurometabolic cascade following head injury [29]. TBI often results in structural and functional changes in the brain which may interact and overlap with the shared macroscopic and microscopic changes in brain structure seen in many psychiatric conditions, thereby increasing the risk of NPD [29], especially in those with pre-injury conditions.
Among TBI patients without any pre-injury psychiatric history, the emerging phenotype was predominately determined by LOS and discharge destination while accounting for the effects of age-related vulnerability to psychiatric disorders. The young males/timely discharge/home recovery sub-phenotype was characterized by a notable proportion of young adults and pediatric patients and showed the lowest NPD-A incidence among all sub-phenotypes. The age-related resilience against physical trauma and NPDs likely underpins the lower incidence of NPDs in this particular sub-phenotype. The highest risk of NPD-A was evident in the older adults/extended recovery/supportive care class. Previous research has shown that prolonged LOS, especially in the intensive care unit, is a risk factor for long-term mental health conditions. Recovering at home with support services and relocation to a nursing home is a challenging transition for older adults, often resulting in high rates of persistent depression and anxiety (Davison et al., 2022). These environmental changes and age-related vulnerability coupled with the recovery from a head injury may worsen the progression of mental health with subsequent development of NPD-A. The young-middle-aged males/extended recovery/rehabilitative care sub-phenotype was also associated with a high incidence of NPD-A. Interestingly, the severity of head injuries observed within this class was especially higher when compared to the other subgroups, suggesting that the extent of functional loss resulting from these injuries necessitated specialized rehabilitative care. Importantly, non-routine discharge to a supportive facility often implies that an individual has experienced functional and/or cognitive decline, which may serve as mediators in the emergence of NPDs. Individuals experiencing limitations in their ability to perform activities of daily living may develop feelings of helplessness and frustration, potentially leading to the development of NPDs. Similarly, cognitive decline after TBI may impede one's ability to process and cope with stressors, increasing vulnerability to psychiatric disorders. Therefore, non-routine discharge to supportive facilities serves as a crucial indicator of functional and/or cognitive loss, which in turn can play a mediating role in the development of NPDs. The current study and data sources did not allow for an analysis of how functional, cognitive, and social outcomes of head injury may be confounders, mediators, and/or modifiers of the association between TBI and NPDs. We acknowledge that a mediation analysis to quantify the extent to which the relationship between TBI and NPDs can be explained by one or more intermediate variables is critical in expanding our understanding of the complex causal pathway between head injury and NPDs.
We identified four distinct latent classes among TBI patients with pre-injury psychiatric history, each exhibiting a unique profile and highlighting the interaction between psychiatric burden and NPD-P incidence. The young adult/low psychiatric burden sub-phenotype was characterized by the lowest burden of pre-existing psychiatric conditions and the lowest NPD-P incidence among all sub-phenotypes. The reduced burden of psychiatric conditions is a likely explanation of the lower incidence of NPD-P in this particular sub-phenotype. In contrast, the psychiatric complexity/high comorbidity class had the highest pre-injury psychiatric comorbidity levels (52%) and were discharged home post-injury. The high burden of psychiatric conditions coupled with the potential lack of screening and monitoring for NPDs in a home environment, may explain why this sub-phenotype had the greatest NPD-P incidence among four classes. Finally, the two sub-phenotypes with intermediate psychiatric burden demonstrated a corresponding intermediate risk of NPDs compared with the other two classes.
Guidelines from the American College of Surgeons emphasize the importance of postinjury mental health screening and intervention for trauma patients [30]. Our approach of identifying interpretable sub-phenotypes with different risk of NPDs, and the accurate classification of individuals into these sub-phenotypes, allows for a practical risk stratification approach of TBI patients. Triaging the risk of NPDs at the time of discharge from hospital may lead to better post-injury mental health outcomes and quality of life for TBI patients.
Strengths and limitations
This study has several strengths. The linked data sources provided detailed information for a population-based cohort, limiting selection and recall biases, while also ensuring robust statistical power. The variables used in our modelling approach are available in electronic health records, and therefore the insights from our analyses are applicable within similar settings. To assess the health burden of NPDs among individuals with and without TBI, a direct comparison of data between TBI cases and uninjured controls is essential. Hence, we employed a demographically similar uninjured cohort as the matched group for TBI patients. This matching approach enables the exploration of differences in NPD prevalence between injured individuals and healthy controls.
There are limitations to be considered when interpreting the current findings. Our results are dependent on patient encounters documented in administrative databases, with the potential for under-reporting of diagnoses, lack of specificity in coding, and inaccuracies in designating diagnostic categories. Given that the current study used administrative health databases, we did not capture lifetime psychiatric history using structured clinical interviews. Our study may have potentially underestimated the true prevalence of pre-injury psychiatric history and its impact on the development of novel psychiatric disorders post-TBI using a lookback period of two years to ascertain pre-injury psychiatric burden. It is also important to acknowledge that while the control group was selected to match TBI patients demographically and did not have a recorded history of TBI or develop TBI during the two years of follow-up, some controls may have experienced head injuries which did not result in clinical encounters.