NEW YORK (Reuters Health) - Dementia associated with Parkinson's disease is distinctively different from that seen in Alzheimer's disease, Norwegian researchers report in the Journal of Neurology, Neurosurgery and Psychiatry.

Dr. Kolbjorn Bronnick at Stavanger University Hospital, Norway, and colleagues conducted a neurological assessment of 488 patients with Parkinson's disease dementia and another 488 patients with Alzheimer's disease, using the Mini-Mental State Examination and the Alzheimer's Disease Assessment Scale-Cognitive Subscale.

The objective of the study by was to assess whether or not a diagnosis could be made based on the results of the cognitive profiles.

"Both groups showed memory impairment, Alzheimer's disease patients performing worse than Parkinson's disease dementia patients," the investigators report. "On the verbal memory tasks in the Alzheimer's Disease Assessment Scale-Cognitive Subscale, however, both groups were clearly impaired relative to a normal control group, with very large effect sizes."

"Poor performance of the Alzheimer's disease patients on the orientation test in Alzheimer's Disease Assessment Scale-Cognitive Subscale best discriminated between the groups, followed by poor performance of the Parkinson's disease dementia patients on the attentional task in Mini-Mental State Examination," Bronnick's team found.

"Diagnosis was predicted from the cognitive profile, with an overall accuracy of 74.7 percent," they report.

"In conclusion," the researchers write, "we found differential cognitive profiles in patients with Parkinson's disease dementia and Alzheimer's disease."

This strongly supports the hypothesis that Parkinson's disease dementia occurs through a mechanism that is quite different than the one associated with Alzheimer's disease, and that there exist pathological and physiological mechanisms specifically related to Parkinson's disease dementia.

SOURCE: Journal of Neurology, Neurosurgery and Psychiatry, October 2007.