Patients with Parkinson disease-related dementia appear to have increased brain atrophy in the hippocampal, temporal and parietal lobes and decreased prefrontal cortex volume compared to patients with Parkinson disease without dementia, according to a report in the December issue of Archives of Neurology, one of the JAMA/Archives journals.

"Patients with Parkinson disease (PD) are at an increased risk of developing dementia (PDD), with cumulative prevalence rates of up to 80 percent," the authors write as background information in the article. "Approximately 25 percent of non-demented PD patients meet neuropsychological criteria for mild cognitive impairment (PD-MCI), which converts to PDD in many cases, and even mild cognitive deficits in PD are associated with functional impairments and worse quality of life."

Daniel Weintraub, M.D., of the Perelman School of Medicine, University of Pennsylvania, Philadelphia, and colleagues, sought to assess the regions and patterns of brain atrophy in patients with PD with normal cognition (PD-NC), patients with PD with mild cognitive impairment (PD-MCI) and patients with PD with dementia-level cognitive deficits (PDD). Data were collected as part of the University of Pennsylvania Center of Excellence for Research on Neurodegenerative Diseases, and the study population included 84 patients with PD (61 PD-NC, 12 PD-MCI and 11 PDD) and 23 healthy control individuals, who all underwent magnetic resonance imaging (MRI) of the brain.

After controlling for other factors (such as patient age, sex and education level), the authors found no between-group differences in regional brain volumes for PD-NC patients compared with participants in the control group. Among patients with PD, there were cognitive group-level differences in hippocampal and medial temporal lobe volumes. Patients in the PD-MCI and PDD groups had smaller hippocampal volumes compared with PD-NC patients, but no differences were observed between patients in the PD-MCI and PDD groups. Patients in the PDD group, but not patients in the PD-MCI group, also had medial temporal lobe atrophy compared with patients in the PD-NC group. The authors found no between-group differences for other brain regions.

Patients in the PD-MCI group had a different pattern of brain atrophy compared to patients in the PD-NC group, but was similar to that of PDD patients. This pattern was characterized by atrophy in hippocampal volume, prefrontal cortex gray and white matter, occipital lobe gray and white matter, and parietal lobe white matter. In non-demented PD patients, the authors found a correlation between memory-encoding performance and hippocampal volume, "suggesting heterogeneity in the neural substrate of memory impairment."

"With growing recognition of Parkinson disease with mild cognitive impairment as common and clinically significant, it will be important to develop consensus diagnostic criteria, validate assessment instruments for use in clinical care and research, and test treatments for their symptomatic and disease-modifying effects," the authors conclude. "Use of a pattern classification approach may allow identification of diffuse regions of cortical gray and white matter atrophy early in the course of cognitive decline."

This study was supported by a health research grant from the Department of Health of the Commonwealth of Pennsylvania from the Tobacco Master Settlement Agreement under Act 2001-77, a grant from the National Institute of Neurological Disorders and Stroke, and grants from the National Institute on Aging.