Introduction It is considered that neuroinflammatory glial response contributes to degenerative process in Parkinson's disease (PD). A translocator protein (TSPO) tracer is established as a marker of neuroinflammation in the brain. A new TSPO tracer [11C]DPA713 has been reported to have a higher affinity for TSPO than a conventional tracer [11C]PK11195. Using this [11C]DPA713 tracer, we specifically focused on microglial activation in the extrastriatal brain region in early-stage PD patients with regard to their memory alterations because some PD patients even at an early stage may suffer mild amnesia or lack of attention.
Methods Fourteen PD patients (mean age 68.2±9.1, Hoenh & Yahr stage 1~2,) without dementia (MMSE>23) or depression (normal SDS) and age-matched healthy controls underwent [11C]DPA713-PET measurements. The binding potential (BP) was estimated by the Logan plot analysis using normalized reference input curves as reported previously. Statistical Parametric Mapping (SPM) was used to compare regional BP levels between the PD and control groups and to examine if microglial activation would differ with comorbidity of amnesia by comparing two subgroups with (n=6) and without (n=8) memory impairment assessed by Rivermead Behavioral Memory Test (RBMT).
Results There were multiple brain regions including the right precuneus showing significantly higher levels of [11C]DPA713 BP in the PD group. In PD patients with memory impairment, the BP levels were shown to be significantly higher in the occipital gyrus than those in healthy controls.
Discussion These results are consistent with the previous reports that microglial activation is present at an early stage of PD. Neuroimflammation developed dominantly in the posterior brain region including the occipital cortex might be related to a deterioration of memory function in the process of PD pathophysiology.