Resting-State fMRI Reveals Tremor Network Alterations in Parkinson’s Disease versus Essential Tremor

Background: Tremor is a main feature of two different movement disorders, Parkinson’s disease (PD) and essential tremor (ET), for which previously published data suggested functionally different underlying brain circuitry.

Objectives: We analyzed resting-state fMRI data of 16 patients: 8 with tremor-dominant PD, and 8 with ET (mean age 74 years). Tremor was predominant in the right upper limb in all patients. In PD, 7 out of 8 were under Levodopa medication at the time of scanning, with a mean dose of 525 mg (range 0–800).

Methods: The functional connectivity of the tremor network has been probed using a seed-to-voxel (further referred to as seed connectivity analysis) and ROI-wise (further referred to as network analysis) approach. Four seeds (dentate nucleus, red nucleus, thalamus, precentral gyrus) in both hemispheres were investigated.

Results: We report exclusive negative functional connectivity (FC) during resting-state in ET between the right dentate and left red nucleus toward the left precentral gyrus. Furthermore, the same connectivity is consistently positive in PD. Conclusions: The major differences in FC between two groups suggest an altered tremor network in PD and ET and further point toward the involvement of the putamen and globus pallidus (both internal and external) on one side, as well as the right ventral anterior thalamic nuclei, on the other side.

Conclusion: In summary, our findings suggest that rs-fMRI could be used as an additional confirmation test, beside the clinical history and examination and the eventual adding of a DAT scan, in the differential diagnosis between PD and ET.