LOS ANGELES—A simple test of finger displacement may distinguish between Parkinson’s disease dementia and Alzheimer’s disease and help neurologists assess the progression of dementia in Parkinson’s disease, according to a study presented at the 70th Annual Meeting of the American Academy of Neurology.
Parkinson’s disease dementia is one of the most disabling nonmotor complications of Parkinson’s disease, but “there is no simple bedside test available that can measure the progression of dementia,” said Aman Deep, MD, a neurology resident at the University of Tennessee Health Science Center in Memphis, and colleagues.
To study the clinical utility of finger displacement in patients with dementia, Dr. Deep and colleagues examined 56 patients with Parkinson’s disease dementia and 35 patients with Alzheimer’s disease. The patients pointed their index fingers toward a grid ruler. After maintaining the pointing position for 15 seconds, patients were asked to close their eyes for another 15 seconds while maintaining the same position. A positive result was downward index finger displacement of 5 cm or greater while patients had their eyes closed.
The patients with Parkinson’s disease dementia (42 male; mean age, 75) had a mean Parkinson’s disease duration of 9.1 years, a mean dementia duration of 3.1 years, and a mean Unified Parkinson’s Disease Rating Scale score of 37. The group’s mean Mini-Mental State Examination (MMSE) score was 17.5. Fifty-three patients out of 56 (95%) exhibited bilateral downward drift of 5 cm or greater, and three patients exhibited less than 5 cm of downward drift. The mean bilateral downward finger drift was 6.8 cm for the group.
Among patients with Alzheimer’s disease (21 male; mean age, 77.4), the mean dementia duration was 3.9 years. The group’s mean MMSE score was 17.8. In the Alzheimer’s disease group, only one patient had minimal drift, and the group’s mean bilateral downward drift was 0.2 cm.
According to the researchers, the finger displacement test has a sensitivity of 100% and a specificity of 92.1%. “Downward finger displacement, especially bilateral downward displacement, may signal extensive disruption of subcortical–cortical circuits,” Dr. Deep and colleagues said. “The simple and inexpensive bedside test of finger displacement may be used to help distinguish Parkinson’s disease dementia from Alzheimer’s disease.”
—Jake Remaly
Suggested Reading
Lieberman A, Deep A, Shi J, et al. Downward finger displacement distinguishes Parkinson disease dementia from Alzheimer disease. Int J Neurosci. 2018;128(2):151-154.
