Hemispatial visual-searching impairment correlated with decreased contralateral parietal blood flow in Alzheimer disease

Background: Impairment of visuospatial attention in Alzheimer disease (AD) has not been fully investigated. Mendez et al reported that patients with A D showed hemispatial biases on visual search tasks. Parietal lobe involveme nt might be related to such impairment. The Picture Description Task is one of the most sensitive tests for detecting language disorders and might be also useful in assessing visual search. Objective: The applicability of the Picture Description Task for evaluating hemispatial visual search impairme nt of AD was investigated, as well as whether the hemispheric difference in parietal blood flow is related to such impairment. Methods: Thirty-four pa tients with AD and age-matched 16 normal subjects performed the Picture Des cription Task. The elements of the picture were divided into three portions : the right portions (five elements), the central portions (two elements), and the left portions (five elements), so as to assess the patients' hemisp atial visual searching ability. Using single photon emission CT, the absolu te regional cerebral blood flow (CBF) values at resting condition were calc ulated by the method of Kuhl et al. Results: Fourteen patients with AD show ed a decreased number of elements pointed out in the left portion of the pi cture, whereas 12 patients had decreased attention in the light portion. Th e remaining eight pointed only to the central portion. None of them showed hemispatial neglect on the figure copying tasks. The patients with decrease d left spatial attention had lower CBF in the right parietal lobe, and vice versa. A significant negative (biologically meaningful) Spearman correlati on was found between the right-left indices of the elements pointed out in the picture and the CBF values. Conclusions: The results suggest that the P icture Description Task is useful for assessing visual search, and impaired hemispatial visual search in AD is related to decreased contralateral pari etal blood flow. The right-left asymmetry of the parietal CBF might be asso ciated with hemispatial visual attention impairments in AD.