Quantitative Assessment of Pathological Tau Burden in Essential Tremor: A Postmortem Study

Essential tremor (ET) patients develop more cognitive impairment and dementia than controls, although there are surprisingly few data on the neuropathological basis for cognitive changes in ET. In this postmortem study, we assessed tau and other pathologies in 26 ET cases and 73 controls (non-ET) (1:3 matching). The mean age = 88.6 years; 55% were cognitively normal, 24% had mild cognitive impairment (MCI), and 20% had dementia. We found similar burdens of pathology using Braak, β-amyloid and Lewy body assessments in ET and controls. In contrast, among cognitively normal subjects, ET cases had a higher number of NFT-positive neurons in the neocortex than controls (p < 0.001); the number of NFT-positive neurons in the medial temporal lobe was similar in these 2 groups (p = 0.22). Among subjects with MCI, ET cases also had higher numbers of NFT-positive neurons in the neocortex than controls (p < 0.001) but again, not in the medial temporal lobe (p = 0.55). Among subjects with dementia, the number of NFT-positive neurons was similar in ET cases and controls. Cognitive function correlated with quantitative neurofibrillary tangle counts in ET cases and controls. In the context of ET, pre-dementia tau burden is higher than in the absence of ET, suggesting a predisposition to tau pathology.