Regular articleAtrophy of hippocampal subfields and adjacent extrahippocampal structures in dementia with Lewy bodies and Alzheimer's disease
Introduction
Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) represent the 2 most common forms of neurodegenerative dementia in elderly (Vann Jones and O'Brien, 2014). Although AD and DLB are characterized by a clinical overlap especially in the early stage, DLB patients show greater attentional and visuoperceptual impairment (Calderon et al., 2001, Collerton et al., 2003) and a less prominent memory loss (Calderon et al., 2001, Ferman et al., 2006) as compared with AD patients. Particularly, visual hallucinations, together with fluctuating cognition and extrapyramidal signs, represent the core clinical feature of DLB (McKeith et al., 2005).
The hippocampus is an heterogeneous brain structure consisting of distinct and specialized regions which process different functions including information consolidation from the episodic memory to the long-term memory, spatial navigation, local spatial representation, and visual perception and/or identification (Bird and Burgess, 2008, Strange et al., 2014).
Although the hippocampal atrophy has been consistently reported in AD and DLB (Barber et al., 2000, Chow et al., 2012, Firbank et al., 2010, Hashimoto et al., 1998, Mak et al., 2015, Sabattoli et al., 2008), the adjacent extrahippocampal structures including entorhinal, perirhinal, and parahippocampal structures have been poorly investigated.
In the present study, we hypothesize that specific alterations of the hippocampal subfields and adjacent extrahippocampal structures could differently contribute to the pathophysiology of AD and DLB. Specifically, based on visual symptoms present in DLB patients, we expect that the extrahippocampal structures which are mainly involved in the visual functions could be impaired in DLB and preserved in AD. To verify this hypothesis, we studied the possible alterations of the hippocampal and extrahippocampal structures in DLB and AD patients by using automated data-analysis approaches (Fischl and Dale, 2000, Van Leemput et al., 2009), which allow to: (1) parcellate the hippocampal subfields and the extrahippocampal structures in different regions and (2) determine their physical measures.
Section snippets
Study sample
This research was approved by the local Ethics Committee and was performed according to the Declaration of Helsinki (1997) and subsequent revisions. All subjects (or their caregivers, where appropriate) provided written informed consent. Nineteen DLB and 15 AD patients were recruited from our Memory Clinic and Movement Disorder Clinic. Nineteen age-matched volunteers were recruited from our nondemented case register cohorts. All subjects were right-handed. Probable AD diagnosis was made in
Demographic and clinical features
Demographic features and neuropsychological test scores were summarized in Table 1.
No differences in terms of age, sex, and educational level were observed among groups.
No differences on global test of cognition (DRS-2, MMSE, CDR) and on the severity of frontal dysfunction (FAB score) were found between AD and DLB patients. Seventeen DLB patients had RBD. All DLB patients had visual hallucinations and cognitive fluctuations. None of the AD patients had visual hallucinations or cognitive
Discussion
In this study, we found different patterns of atrophy within the hippocampal subfields and the adjacent extrahippocampal structures in DLB and AD patients (Fig. 2).
Specifically, the CA, DG, and subiculum were overall more atrophic in AD patients. Neuropathological studies have reported that AD and its prodromal stages are associated with neuronal loss in the CA1 and the subiculum regions (Corder et al., 2000, Kerchner et al., 2012, Thompson et al., 2003). Furthermore, it was observed that the
Disclosure statement
The authors have no conflicts of interest to disclose.
Acknowledgements
This study was supported by Italian Ministry of Health (Ministero della Salute); Grant number: GR-2010-2313418.
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