Recent Advances in Chronic Traumatic Encephalopathy.

Exposure to repeated head impacts (RHIs), such as those experienced in contact sports or military service, can lead to the development of chronic traumatic encephalopathy (CTE), a neurodegenerative tauopathy. CTE cannot be diagnosed during life, only by post-mortem neuropathologic examination. The pathognomonic lesion of CTE consists of a perivascular accumulation of hyperphosphorylated tau as neurofibrillary tangles and dotlike neurites, preferentially at the depths of cortical sulci. The biomechanics of RHI involve acceleration, deceleration, and rotational forces that distort brain tissue and strain fragile structures, such as blood vessels and axons, especially in the crevices of the brain, where these forces are localized. CTE is unique from other tauopathies in its molecular structure, pattern, and regional distribution of tau. Studies in American football, rugby, and ice hockey players demonstrate a dose-response relationship between years of exposure to sport and increased CTE risk and severity. The clinical symptoms associated with CTE are classified as traumatic encephalopathy syndrome. Exposure to RHI also increases the deposition of other pathologic proteins, including β-amyloid, α-synuclein, and transactive response DNA-binding protein (TDP-43), raising the risk for other neurodegenerations, such as Alzheimer disease, Lewy body disease, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis.