Efficacy of a repeat testing protocol for cognitive fatigue assessment: a preliminary study in postconcussive syndrome participants

Mental Fatigue after Mild Traumatic Brain Injury in Relation to Cognitive Tests and Brain Imaging Methods

Most people recover within months after a mild traumatic brain injury (TBI) or concussion, but some will suffer from long-term fatigue with a reduced quality of life and the inability to maintain their employment status or education. For many people, mental fatigue is one of the most distressing and long-lasting symptoms following an mTBI. No efficient treatment options can be offered. The best method for measuring fatigue today is with fatigue self-assessment scales, there being no objective clinical tests available for mental fatigue. The aim here is to provide a narrative review and identify fatigue in relation to cognitive tests and brain imaging methods. Suggestions for future research are presented.

Neurophysiological abnormalities in individuals with persistent post-concussion symptoms

Concussion injury results in a rapid onset of transient neurological impairment that can resolve quickly, or sometimes evolve over time, but usually resolve within seven to 10 days. However, a small but noticeable cohort (~10%) of individuals continues to experience persistent lingering effects, particularly fatigue, recognized as post-concussion symptoms (PCS). This study explored neurophysiological mechanisms in people with persistent PCS. Studies involved using self-report post-concussion fatigue scale, transcranial magnetic stimulation (TMS) and somatosensory stimulation in those with diagnosed PCS (n = 20; 36.1 ± 14.0 yr., 4 female; mean time post-concussion 15.4 ± 7.6 months) to fully recovered individuals (n = 20; 33.8 ± 6.6 yr., 2 female; post-concussion 12.9 ± 6.6 months) and healthy controls (n = 20; 37.7 ± 8.0 yr., 3 female). PCS participants demonstrated a significantly higher self-report fatigue (score: PCS 20.2 [95% CI 17.4-22.9], Recovered 6.2 [3.1-9.3], Control 2.75 [0.6-4.8]). PCS participants showed a worsening of reaction time (F_2,57 = 4.214; p = 0.020) and increased reaction time variability (F_2,57 = 5.505; p = 0.007). Somatosensory differences were observed for amplitude discrimination (F_2,57 = 5.166; p = 0.009), temporal order judgment (F_2,57 = 4.606; p = 0.014) and duration discrimination (F_2,57 = 6.081; p = 0.004). Increased intracortical inhibition in TMS single pulse suprathreshold stimulation (110%: F_2,57 = 6.842; p = 0.002; 130%: F_2,57 = 4.900; p = 0.011; 150%: F_2,57 = 4.638; p = 0.014; 170%: F_2,57 = 9.845; p < 0.001) and paired pulse protocols was also seen (SICI: F_2,57 = 23.390; p < 0.001, and LICI: F_2,57 = 21.603; p < 0.001). Using non-invasive stimulation techniques, this novel study showed increased cortical inhibition and compromised central information processing, suggesting neural mechanisms underpinning ongoing fatigue, allowing for potential clinical rehabilitation strategies.