Visuospatial dysfunction may be a key in the differentiation between Alzheimer's disease and subcortical cognitive impairment in moderate to severe stages.

AIMS: Recent studies have suggested that subcortical cognitive impairment (SubCI) and Alzheimer's disease (AD) can be differentiated by visuospatial tasks. We addressed at what severity stage these differences become apparent and what components in visuospatial processes are subject to impairment. METHODS: Sixty patients with AD, 22 with vascular cognitive impairment and 63 with extrapyramidal diseases with cognitive impairment were assessed using the revised Hasegawa Dementia Scale (HDSR), clock drawing/reading/matching tests (CDT, CRT, CMT), figure copying (FIG) and Frontal Assessment Battery (FAB). Patients were categorized according to the HDSR scores in order to control for the severity of global cognitive impairment. Raw scores were converted to Z-scores for comparisons. RESULTS: In the mild stage, results of all measures were comparable between AD and SubCI. In the moderate-severe stage, scores of CDT, CRT, CMT, FIG and FAB were significantly lower in SubCI. The results suggest that (given that global cognition is controlled for) visuo-perception, visuo-construction and semantic-numerical analyses of visual information may be more impaired in SubCI than AD. CONCLUSIONS: AD and SubCI may be difficult to be differentiated in the mild stages, and the visuospatial cognitive system may be extensively defective in SubCI.