Entorhinal cortex atrophy differentiates Parkinson's disease patients with and without dementia

Volumetric measures of mesial temporal lobe structures on MRI scans recently have been explored as potential biomarkers of dementia in patients with PD, with investigations primarily focused on hippocampal volume. Both in vivo MRI and postmortem tissue studies in Alzheimer's disease, however, demonstrate that the entorhinal cortex (ERC) is involved earlier in disease-related pathology than the hippocampus. The ERC, a region integral in declarative memory function, projects multimodal sensory information to the hippocampus through the perforant path. In PD, ERC atrophy, as measured on MRI, however, has received less attention, compared to hippocampal atrophy. We compared ERC and hippocampal atrophy in 12 subjects with PD dementia including memory impairment, 14 PD subjects with normal cognition, and 14 healthy controls with normal cognition using manual segmentation methods on MRI scans. Though hippocampal volumes were similar in the two PD cognitive groups, ERC volumes were substantially smaller in the demented PD subjects, compared to cognitively normal PD subjects (P < 0.05). In addition, normalized ERC and hippocampal volumes for right and left hemispheres were significantly lower in the demented PD group, compared to healthy controls. Our findings suggest that ERC atrophy differentiates demented and cognitively normal PD subjects, in contrast to hippocampal atrophy. Thus, ERC atrophy on MRI may be a potential biomarker for dementia in PD, particularly in the setting of memory impairment.