Chronic Traumatic Encephalopathy Neuropathologic Change is Infrequent Following Isolated Moderate-Severe Traumatic Brain Injury

Chronic traumatic encephalopathy-neuropathologic change (CTE-NC) has been primarily studied in contact sport athletes with repetitive head impacts (RHI). An association with isolated traumatic brain injury (TBI) is less clear. We systematically reviewed the autopsied cohort of Late Effects of TBI (LETBI), characterized primarily by isolated TBI but also including RHI, for features of CTE-NC. A consecutive series of 44 brains underwent comprehensive neuropathologic evaluation, exceeding recommended CTE consensus protocols. Of the 44, 6 (13.6%) (age range, 3 ^rd -7 ^th decades; median, 6 ^th decade) had CTE-NC, forming the basis for this exploratory analysis. Ex vivo neuroimaging (in 4 of 6) highlighted traumatic and white matter microvascular lesions, facilitating histological sampling of subtle neuropathologies that might otherwise have been missed by conventional sectioning. Macroscopically, 5 had cortical (contusional) and white matter (torsional) volume loss, with septal lesions and hydrocephalus ex vacuo (i.e., structural lesions of moderate-severe TBI). Microscopically, tau-immunopositive neuronal and astrocytic pathology in a perivascular arrangement within sulcal depths met current pathognomonic criteria for CTE-NC in 5 (3 “low” and 2 “high” burden); 1 had more limited findings considered “suspicious” for CTE-NC. Five of 6 cases with any CTE-NC reported substantial exposure to RHI, through contact sport ranging over at least 16 years. One case had no known exposure to RHI: this case (death: 6th decade) had 2 isolated severe TBIs (sustained 30y and 3y prior to death). Of note, one case with “high” CTE also had Alzheimer Disease Neuropathologic Change (high stage), Lewy Body Disease (limbic), and TDP43 accumulation (“polyproteinopathy”). Aging-related tau astrogliopathy, mostly subpial, was seen in 4 cases. Glial tau was also noted around old cavitary contusions in 2. These findings converge with prior studies demonstrating that CTE is largely associated with RHI and is infrequent among individuals with isolated TBI.