Heterogeneity of Monosymptomatic Resting Tremor in a Prospective Study： Clinical Features, Electrophysiological Test, and Dopamine Transporter Positron Emission Tomography

Background： The relationship between monosymptomatic resting tremor （mRT） and Parkinson＇s disease （PD） Iemains controversial. In this study, we aimed to assess tile function ofpresynaptic dopaminergic neurons in patients with mRT by dopamine transporter positron emission tomography （DAT-PET） and to evaluate the utility of clinical features or electrophysioIogical studies in differential diagnosis. Methods： Thirty-three consecutive patients with toRT were enrolled prospectively. The Unified Parkinson＇s Disease Rating Scale and electromyography were tested before DAT-PET. Striatal asymmetry index （SAI） was calculated, and a normal DATPET was defined as a SAI of 〈15%. Scans without evidence of dopaminergic deficits （SWEDDs） were diagnosed in patients with a subsequent normal DAT-PET and structural magnetic resonance imaging. Results： Twenty-eight toRT patients with a significant reduction in uptake of DAT binding in the striatum were diagnosed with PD, while the remained 5 with a normal DAT-PET scan were SWEDDs. As for UPRDS, the dressing and hygiene score, walking m motor experiences of daily living （Part I1） and motor examination （Part Ill ） were significant different between two groups （P 〈 0.05 and P 〈 0.01, respectively）. Bilateral tremor was more frequent in the SWEDDs group （P 〈 0.05）. The frequency of resting tremor and the amplitude ofpostural tremor tend to be higher in the SWEDDs group （P = 0.08 and P= 0.05, respectively）. Conclusions： mRT is heterogeneous in presynaptic nigrostriatal dopaminergic degeneration, which can be determined by DAT-PET brain imaging. Clinical and electrophysiological features may provide clues to distinguish PD from SWEDDs.