Clinical Correlates of Cerebral Amyloid Deposition in Parkinson's Disease Dementia: Evidence from a PET Study.

Background: Dementia in Parkinson's disease (PDD) is common presumably due to combined neuropathological substrates. Amyloid-β (Aβ) plaques are well described in PDD but their contribution in synucleinopathies is still controversial.

Objective: To investigate regional [18F]Florbetapir binding and its relative contribution to cognitive dysfunction in a cohort of PDD patients and to test whether PDD patients with comorbid amyloidopathy have different clinical and neuropsychological characteristics.

Methods: 21 PDD patients, 20 with Alzheimer's disease (AD), and 9 control subjects underwent amyloid positron emission tomography (PET) imaging, neurological, and neuropsychological assessment. Radioligand binding was compared across the groups. PDD scans were interpreted qualitatively and semiquantitatively and categorized as positive or negative. Annual longitudinal Mini-Mental State Examination (MMSE) of PDD subjects was retrospectively collected in order to relate Aβ burden to the course of cognitive impairment.

Results: [18F]Florbetapir PET imaging was positive in 11 PDD patients (52.38%) using the semi-quantitative method. There were no group differences between PDD subjects with increased cortical [18F]Florbetapir (+) and those without (-), according to demographic and clinical parameters. PDD+ performed worse on Digit Span Foward and on Rey Auditory Verbal Learning Test delayed recall than the PDD- with a significant negative correlation between global cortical retention and specific memory tests. Aβ load did not correlate with MMSE ratings although PDD+ demonstrated a faster clinical progression of dementia.

Conclusions: Significant Aβ deposition is common in PDD patients contributing to memory impairment and driving a faster rate of cognitive decline.