Alzheimer's disease severely affects areas of the claustrum connected with the entorhinal cortex.

Pathological changes in the claustrum and its main parts (dorsal, temporal, orbital and paramygdalar) were studied on ten brains of patients with Alzheimer's disease and five control brains. The brains after fixation in formalin were embedded in paraffin, coronal-8-micron-thick serial sections were cut and stained either with cresyl violet or with immunocytochemical methods for amyloid and tangles. Morphometrical studies were performed in all parts of the claustrum along its whole extension. The claustrum in control brains was free of neurofibrillary and amyloid pathology except for one case with few senile plaques in the paramygdalar part. In AD affected brains the most severe changes were found in the paramygdalar part connected with the entorhinal cortex (neuronal loss -46%; 698 +/- 244.6 neurofibrillary tangles per mm3, tangle/neuron ratio -6.8 +/- 2.4%). In other parts of the claustrum related mainly with the neocortex pathological changes were significantly less expressed. As pathological AD type alteration affects severely practically the whole hippocampal formation, including the entorhinal cortex, the extensive neuronal pathology of the paramygdalar part of the claustrum is probably related to this process and may deeper memory dysfunction.