Factors associated with resistance to dementia despite high Alzheimer disease pathology

Abstract

Background: Autopsy series have shown that some elderly people remain with normal cognitive function during life despite having high burdens of pathologic lesions associated with Alzheimer disease (AD) at death. Understanding why these individuals show no cognitive decline, despite high AD pathologic burdens, may be key to discovery of neuroprotective mechanisms. Methods: A total of 36 subjects who on autopsy had Braak stage V or VI and moderate or frequent neuritic plaque scores based on Consortium to Establish a Registry for Alzheimer's Disease (CERAD) standards were included. Twelve had normal cognitive function and 24 a diagnosis of AD before death. Demographic characteristics, clinical and pathologic data, as well as antemortem brain volumes were compared between the groups. Results: In multiple regression analysis, antemortem hippocampal and total brain volumes were significantly larger in the group with normal cognitive function after adjusting for gender, age at MRI, time from MRI to death, Braak stage, CERAD neuritic plaque score, and overall presence of vascular disease. Conclusion: Larger brain and hippocampal volumes were associated with preserved cognitive function during life despite a high burden of Alzheimer disease (AD) pathologic lesions at death. A better understanding of processes that lead to preservation of brain volume may provide important clues for the discovery of mechanisms that protect the elderly from AD. AD = Alzheimer disease; CDR = Clinical Dementia Rating Scale; CERAD = Consortium to Establish a Registry for Alzheimer's Disease; CIRS = Cumulative Illness Rating Scale; ICV = intracranial volume; LB = Lewy bodies; MMSE = Mini-Mental State Examination; NCSE = Neurobehavioral Cognitive Status Examination; NFT = neurofibrillary tangle; NIA = National Institute on Aging; NP = neuritic plaques; OHSU = Oregon Health & Science University; Ref = reference; SES = socioeconomic status; UPDRS = Unified Parkinson's Disease Rating Scale.