Positron emission tomography imaging of the cholinergic system in parkinsonian tremor

It is believed that anticholinergics alleviate tremor and rigidity in Parkinson's (PD) by counteracting a relative cholinergic overactivity in motor regions, but this remains unclear. This study aimed to investigate possible cholinergic alterations in tremor dominant (TD) PD that may back use of anticholinergics.

Twelve PD patients [six with TD and six with non-tremor dominant (nTD) phenotype] and six healthy controls (HC) underwent cholinergic positron emission tomography with [¹¹C]-donepezil. Participants were assessed with the Movement Disorder Society-Unified Parkinson's Disease Rating Scale.

We found no increases of [¹¹C]-donepezil binding in cortical or subcortical areas of either PD group compared with HC. Compared with HC, [¹¹C]-donepezil binding was significantly decreased in the thalamus of nTD patients (p = 0.0463) but not in TD patients. This was confirmed by voxel-wise analyses that found further significant decreases in hippocampus, caudate, parahippocampus, cerebellar vermis, and lower part of mesencephalon of nTD PD patients compared with HC (p = 0.000). However, no significant differences in [¹¹C]-donepezil binding were found in the direct comparison between TD and nTD PD patients.

Our study provides evidence that TD PD patients might have relatively preserved cholinergic function in tremor-associated regions. However, anticholinergics should be used with caution when treating parkinsonian tremor due to their side effect profile.