Alzheimer's Disease Pathology Outside of the Cerebrum Is Related to a Higher Odds of Dementia

Background: Assessments of Alzheimer's disease pathology do not routinely include lower brainstem, olfactory bulb, and spinal cord. Objective: Test if amyloid-beta (A beta) and paired helical filament (PHF) tau-tangles outside the cerebrum are associated with the odds of dementia. Methods: Autopsies were obtained in decedents with cognitive testing (n = 300). A beta plaques and PHF tau-tangles were assessed in 24 sites: cerebrum (n = 14), brainstem (n = 5), olfactory bulb, and four spinal cord levels. Since spinal A beta were absent in the first 165 cases, it was not assessed in the remaining cases. Results: Age at death was 91 years old. About 90% had A beta in cerebrum and of these, half had A beta in the brainstem. Of the latter, 85% showed A beta in the olfactory bulb. All but one participant had tau-tangles in the cerebrum and 86% had brainstem tau-tangles. Of the latter, 80% had tau-tangles in olfactory bulb and 36% tau-tangles in one or more spinal cord levels. About 90% of adults with tau-tangles also had A beta in one or more regions. In a logistic model controlling for demographics, A beta and tau-tangles within the cerebrum, the presence of A beta in olfactory bulb [OR, 1.74(1.00, 3.05)]; tau-tangles in brainstem [OR, 4.00(1.1.57,10.21)]; and spinal cord [OR, 1.87 (1.21,3.11)] were independently associated with higher odds of dementia. Conclusions: Regional differences in A beta and tau-tangle accumulation extend beyond cerebrum to spinal cord and their presence outside the cerebrum are associated with a higher odds of dementia. Further studies are needed to clarify the extent, burden, and consequences of AD pathology outside of cerebrum.