Hippocampal abnormalities and memory deficits in Parkinson disease: a multimodal imaging study

Investigating in a case-control study whether the performance scores of a group of patients with Parkinson disease (PD) without dementia on tests of declarative memory could be predicted by hippocampal volume reduction (as assessed by automatic segmentation of cerebral magnetic resonance [MR] images) or by the rate of microstructural alterations (as evaluated by diffusion tensor analysis of MR images).

Twenty-five individuals with PD and 25 matched healthy control subjects underwent a 3-T MRI protocol with whole-brain T1-weighted and diffusion tensor imaging and a neuropsychological assessment. Images were processed to obtain indices of macrostructural (volume) and microstructural (mean diffusivity [MD]) variation of bilateral hippocampi. Neuropsychological evaluation included tests of verbal memory (15-minute delayed recall of a 15-word list) and visuospatial memory (20-minute delayed reproduction of Rey complex figure).

MD in the hippocampi of patients with PD was significantly increased with respect to that of the group of control subjects. Moreover, patients with high hippocampal MD values obtained low memory scores. In contrast, no difference emerged between patients with PD and healthy control subjects for hippocampal size, and no relationship could be found between hippocampal volumes and memory scores.

These data confirm that the declarative memory impairment in patients with PD without dementia may be predicted by the rate of microstructural alterations in the hippocampal formation as detected by diffusion tensor imaging analysis.