Sleep quality may explain the connection between mood dysregulation and neurodegeneration following TBI

By Lori Mae Yvette Calibuso Acob. This article was initially published in our Concussion Update newsletter; please consider subscribing.

A study by Jackie L. Gottshall et al. found that poor sleep quality may be an "important driver of the relationships" between common post-mTBI neuropsychiatric disorders—major depressive disorder (MDD), post-concussive symptoms (PCS), and post-traumatic stress disorder (PTSD)—and biomarkers of neurodegeneration.

The study, published in Brain Injury, included 143 current and former U.S. military Service Members (ages 18+) exposed to combat during post-9/11 conflicts who sustained a mild TBI. The researchers wanted to assess if sleep symptoms played a unique role in the associations of MDD, PCS, and PTSD with neurodegenerative outcomes.

In assessing neuropsychiatric symptoms following mTBI, the study used self-reported assessments of sleep quality (PSQI), MDD (PHQ-9), PTSD (PLC-5), and PCS (NSI). Three of these assessment tools (PHQ-9, PLC-5, and NSI) have at least one item about sleep. To determine the unique role of sleep symptoms in post-mTBI neuropsychiatric disorders, the researchers compared composite scores according to the inclusion or exclusion of sleep items. The researchers also wanted to evaluate if the composite scores of PHQ-9, PLC-5, and NSI were similar to PSQI scores. Analyzing this data would provide insight into whether sleep quality influences correlations between MDD, PTSD, and PCS.

Gottshall et al. found that, regardless of whether sleep symptoms were included or excluded in the comparison of PHQ-9, PLC-5, and NSI surveys, each composite score showed similar relationships with biomarkers of neurodegeneration and mTBI. This finding suggests that "correlations with neurodegenerative biomarker levels may not be specific to the sleep items themselves." However, the researchers did discover that each self-report measure had "strong and congruent correlations" with PSQI (sleep quality) scores, suggesting a "strong effect of sleep quality on non-sleep symptoms." The authors conclude that the "congruency of associations raises the possibility of a common pathophysiological process underlying differing symptomologies. Given its role in neurodegeneration and mood dysregulation, sleep physiology seems a likely candidate." 

Although this study had the strengths of employing standardized measures of mTBI that ensure relative homogeneity and generalizability, it's crucial to acknowledge that MDD, PTSD, and the various symptoms of PCS are not exclusive to TBI-associated pathophysiology. The sleep symptoms observed in this study may be similar in individuals without brain injuries, affecting the authors' ability to draw conclusions specific to mTBI. However, this study does introduce new hypotheses that can be examined in future studies to further understand the influence of sleep quality on the connection between mood dysregulation and neurodegeneration following TBI.