Mild cognitive impairment (MCI) was conceptualized as a prodrome of Alzheimer’s disease (AD), and its original definition focused on memory impairment. Later, assuming that non-AD dementia subtypes (e.g. dementia with Lewy bodies, vascular dementia) may manifest its early symptoms other than memory, MCI was dichotomized into amnestic MCI (aMCI) and non-amnestic MCI (naMCI). However, recent evidence has found that AD could be converted from naMCI as well as aMCI. In addition, while depressive symptoms have been reported to increase the risk of AD in aMCI, it has not been clear if this is also true in naMCI.
The researchers examined the longitudinal course of 802 non-demented participants in a Japanese rural community for up to 7 years. They analyzed the impact of depressive symptoms on the transition from aMCI or naMCI to AD, and cognitively normal to aMCI, naMCI or AD.
The criteria defining a depressive state were determined by the Geriatric Depression Scale. MCI was diagnosed on the basis of a) cognitive complaints, b) objective impairment in one or more cognitive domains (attention, memory, visuospatial function, language and reasoning) based on the average of scores of a cognitive test battery within that domain and a cut-off of -1SD, adjusting for age, gender and years of education, c) essentially preserved activities of daily living (ADL), and d) no diagnosis of dementia. Dementia and its subtypes were diagnosed based on the standard criteria.
The presence of depressive symptoms increased the risk of developing AD in the aMCI group, but not in the naMCI group. In the cognitively normal group, the presence of depressive symptoms increased the risk of aMCI, but not of naMCI or AD.
The differing impacts of depressive symptoms on the development of AD suggest that the relationship between depressive symptoms and cognitive impairment could differ in aMCI and naMCI goups. While aMCI with depressive symptoms may be a reliable prodrome of AD, naMCI with depressive symptoms may not.
Jiro Kida, MD
Graduate School of Comprehensive Human Sciences,
University of Tsukuba, Ibaraki, Japan
Jiro Kida, Kiyotaka Nemoto, Chiaki Ikejima, Shogyoku Bun, Tatsuyuki Kakuma, Katsuyoshi Mizukami, Takashi Asada. Impact of depressive symptoms on conversion from mild cognitive impairment subtypes to Alzheimer’s disease: A community-based longitudinal study. The article will be published in the Journal of Alzheimer’s Disease 51(2)（DOI: 10.3233/JAD-150603）.
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