The effects of persistent mild traumatic brain injury symptoms on the neurophysiological health of adults

BACKGROUND: Mild traumatic brain injury (mTBI) accounts for approximately 70-90% of the 2.8 million TBIs sustained annually, and up to 40% of those may result in persistent symptoms lasting beyond a normal clinical recovery timeline. Persistent concussion symptoms (PCS) can manifest into life-changing disabilities, lost work and financial income, elevated risks of depression and anxiety, and reduced quality of life (QoL), as well as more subtle deficits in the ability to perform a cognitive and motor task concurrently, a common activity of daily living. Dual-task gait conditions have revealed the adaptation of a conservative gait strategy following mTBI in young athletes, however it is unknown if this strategy is present among adults with PCS. Together an assessment of symptoms, QoL, cognition, and postural control can provide an overall understanding of the subtle deficits in an adult PCS population. PURPOSE: The overall purpose of this dissertation was to identify and quantify neurophysiological impairments in adults with PCS. METHODS: For aim 1, PCS patients (n=15, 43.9+11.8 years, 11 females, 110-1314 days since injury) and healthy controls (n=24, 41.6+10.4 years, 16 females) performed dual-task gait and gait initiation conditions in a motion capture laboratory. Dual-task costs were calculated for gait, gait initiation, and cognitive variables to determine task prioritization. For aim 2, the same PCS patients and healthy controls completed questionnaires to assess symptoms and quality of life, performed a variety of common post-concussion clinical assessments (i.e.: Clinical Reaction Time, King-Devick, Tandem gait task), and a brief sensorimotor and cognitive assessment on the Kinesiological Instrument for Normal and Altered Reaching Movements (KINARM, Kingston, Ontario). Once normality was established, groups were compared using either an independent samples t-test (normal distribution) or a Mann-Whitney U test (non-normal distribution). Additionally, for aim 2, we examined the associations between KINARM variables and clinical assessment performance using a Pearson correlation test. A point-biserial correlation was run to determine the relationship between KINARM variables and VOMS failure (a categorical variable). RESULTS: For aim 1, PCS patients had significantly worse DTCs for gait (e.g.: Gait Speed DTCs: PCS = -13.1 + 11.9%, Controls = -4.3 + 6.4%, p = 0.009, d = .921) and gait initiation (e.g.: APA phase M/L displacement (-34.8 + 21.8% and -10.6 + 25.3%, p = .004, d = 1.01) when compared to the healthy controls. For aim 2, PCS patients had significantly worse symptoms, psychological issues, and overall quality of life compared to healthy controls (e.g.: Rivermead number of symptoms (Range = 0-16): PCS = 13.5 + 2.2, Controls = 4.0 + 3.8, p < .001, r = .794). Additionally, PCS patients had significantly worse performance on most clinical assessments (e.g.: clinical mean reaction time: PCS = 238.3 + 47.3 msec, Controls = 208.3 + 18.0 msec, p = .035, r =.337), however no significant differences between groups were observed on any of the tandem gait task variables. No significant differences were observed between groups on the predominantly motor-based KINARM tasks (e.g.: Trail-Making Test A: PCS = 62.0 + 57.8 sec, Controls = 37.1 + 8.4 sec, p = .106, r = .254), however several significant differences were observed between groups on the more cognitively demanding tasks (Trail-Making Test B: PCS = 76.3 + 62.8 sec, Controls = 42.3 + 10.4, p = .044, r = .324). DISCUSSION: These results suggest that adults experiencing persistent concussion symptoms have impairments when performing a dual task, which reflects a conservative gait strategy when additional cognitive resources are required to perform a cognitive and a motor task concurrently. This study also identified more subtle sensorimotor and cognitive deficits in PCS patients using the novel KINARM assessment tool, further suggesting that adults with persistent concussion symptoms have impaired cognitive function when required to perform an upper body cognitive-motor dual task. Furthermore, as expected, the PCS patients had worse self-reported symptoms, psychological issues, and quality of life, as well as performance on clinical tests for post-concussion assessment of neurophysiological health. This suggests that these assessments, which have primarily been used on high school and college student-athletes, are also able to identify patients experiencing persistent concussion symptoms.

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