Objective: To investigate the difference of dopaminergic neuronal loss between PD patients with dopamine-unresponsive and -responsive resting tremor.

Background: Resting tremor (RT) is one of the cardinal motor features of Parkinson’s disease (PD). Responsiveness of resting tremor to dopaminergic treatment is quite variable. Furthermore, it has not been reported yet that whether there is a difference of dopaminergic neuronal loss between PD patients with dopamine-unresponsive and -responsive resting tremor.

Methods: Between September 1st 2012 and July 31th 2016, fifteen tremor dominant PD cases were obtained from neurology clinic stipulating: no evidence of Parkinson-plus syndrome; no other abnormal neurological signs or exposure to tremor reducing drugs. We defined the dopamine-responsiveness of resting tremor as a reduction of at least two points or changing to zero point for more than 3 months in the UPDRS tremor score of the limb with prominent resting tremor[1]. All patients had underwent [18F]FP-CIT PET on OFF state within 1 year after PD diagnosis. FP-CIT PET images were quantitatively analyzed using 12 striatal subregions and two substantia nigra VOI templates. Subregional binding ratio (BR), inter-subregional ratio of BR (ISR) and subregional asymmetry index were compared between two groups.

Results: There were 5 men and 10 women (Average age=59.5 ± 9.6). The mean age of onset was 59.7 ± 10.2 years. The mean disease duration was 3.33 ± 1.68 years. Four patients’ resting tremor showed an improved performance after the medical therapy, yet the other eleven patients’ resting tremor remained still. Current age, disease duration, H & Y stage, levodopa equivalent dose, and UPDRS part III score at OFF time revealed no statistical difference in both groups.  On quantitative analysis of FP-CIT PET, BR for ventral striatum in patients with dopamine-unresponsive resting tremor was significantly higher than that in patients with dopamine-responsive resting tremor (3.85 ± 0.70 vs. 3.00 ± 0.36, P < 0.05). The BR for all striatal subregions in patients with dopamine-unresponsive resting tremor were higher than those in patients with dopamine-responsive resting tremor, but those were not significant.

Conclusions: This study suggests that nigral dopaminergic neuronal loss in PD patients having dopamine-unresponsive resting tremor can be less severe.

References: [1] Mov Disord. 2008 Jan;23(1):137-40. Factors predicting response to dopaminergic treatment for resting tremor of Parkinson’s disease. Sung YH, Chung SJ, Kim SR, Lee MC.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-relative-preservation-of-the-dopaminergic-neuroal-loss-of-patients-with-parkinsons-disease-having-dopamine-unresponsive-resting-tremor/