Selective disconnection of specific visual association pathways in cases of Alzheimer's disease presenting with Balint's syndrome.

During a recent clinical and neuropathological evaluation of a large autopsy population of brains our attention was drawn to a subset of patients with Alzheimer's disease (AD) presenting with a major impairment of visuospatial skills referred to as Balint's syndrome. In this subset a shift in the distribution of certain pathological profiles had occurred in that the visual areas of the occipital and posterior parietal regions had an increased number of lesions, whereas the prefrontal cortex had fewer lesions than usually observed in AD. Previous quantitative analyses have shown that generally in AD, primary sensory cortical areas are less damaged than association areas of the frontal and temporal lobes, as demonstrated by the laminar and regional distribution of two neuropathological features of the disease, neurofibrillary tangles and neuritic (senile) plaques. The distribution of pathological lesions in the AD cases with Balint's syndrome revealed that specific visual association pathways were disrupted, which are normally spared in AD. These data suggest that in some cases of AD, the particular psychological and neurological symptomatology may be caused by the selective loss of specific corticocortical systems, as reflected in the differential distribution of the neuropathological markers of the disease.