Striatal Dopaminergic Function and Motor Slowing in Essential Tremor Plus

Area of Science:

• Neuroscience
• Neurology
• Radiology

Background:

• Essential tremor (ET) typically shows normal striatal dopamine transporter (DAT) binding.
• Emerging evidence suggests a partial dopaminergic mechanism in ET, especially in ET patients with additional neurological signs (ET+).
• An epidemiological link exists between ET and Parkinson's disease (PD).

Purpose of the Study:

• Investigate the dopaminergic pathophysiology in ET+.
• Compare dopaminergic function in ET+ to Parkinson's disease (PD).

Main Methods:

• [123I]FP-CIT SPECT imaging and clinical examinations were performed on 43 ET+ patients, 115 PD patients, and 40 healthy controls.
• Median follow-up of 3.0 years for diagnosis confirmation.
• Extended follow-up (median 7.7 years) for ET+ patients.
• Region-specific striatal DAT binding ratios were compared and correlated with MDS-UPDRS motor scores.

Main Results:

• Bradykinesia scores negatively correlated with posterior putamen DAT binding in both ET+ and PD groups.
• The strongest correlation between bradykinesia and DAT binding was observed in finger tapping.
• In ET+ patients, kinetic tremor asymmetry correlated with posterior putamen DAT binding asymmetry, indicating subtle contralateral DAT loss with more severe tremor.

Conclusions:

• Subtle bradykinesia in ET+ correlates with striatal dopaminergic dysfunction.
• Kinetic tremor asymmetry in ET+ is associated with hemispheric DAT binding asymmetry.
• Findings support partial dopaminergic involvement in the pathophysiology of ET+.