Objective: To assess the prevalence of internal tremor in a cohort of PD versus ET patients and its association with non-motor symptoms.

Background: Internal tremor (IT) can be defined as the subjective feeling of tremor in the extremities or trunk without actual visible movement. It remains a poorly described symptom in tremor-associated conditions such as Parkinson’s disease (PD) and essential tremor (ET).

Method: A cohort study was performed in Jan-March 2022. Inclusion criteria were age over 18y, diagnosis of PD or ET or referral due to upper limb tremor. Patients completed a questionnaire about the IT, HADS and MDS-NMSQ to assess anxiety/depression and non-motor symptoms. Descriptive and comparative analysis of different variables and comparative study using chi-square, t-tests, and non-parametric tests were used when applicable.

Results: We included 23 patients with PD and 18 with ET. The groups didn’t differ on gender, and there was a difference in age [72 in PPD vs 67 years in PTE, t(40)=2,1; p=0,043]. Median HADS-D was 4 (0-11;Q1-Q3=2-7) and 3 (0-11;Q1-Q3=2-6) and HADS-A was 3 (0-11;Q1-Q3=2-7) and 3 (0-11;Q1-Q3=2-6) in DP and ET, respectively – there was no difference in the 2 groups nor in mean NMSQ. 26% of patients (n=11) reported IT, 26% in PD and 22% in ET. There was no significant difference. The most reported location was the chest (54,5%) and 63,6% felt IT in different areas from observable tremor. 72,8% patients related IT to anxiety, and it was alleviated by relaxing techniques (breathing, sleeping, yoga) in 36% or mobilization in 27% of cases. In 44,5%, IT was as much or more disturbing than the visible tremor. IT was not correlated to age [t(40)=-0,954; p=0,346), gender [X²(1;n=42)=0,74; p=0,390], PD [X²(1; n=42)=0; p=0,987] or ET [X²(1;n=42)=0,257; p=0,612]. There was no correlation between IT and NMS score [t(39)=-0,685; p=0,415), HADS-A or D (U=162;p=0,328 and U=135;p=0,941, respectively). On NMS sub-analysis, patients with IT tended to refer sensation of incomplete evacuation [X²(1;n=41)=3,192; p=0,074) and vivid dreams (X²(1;n=42)=3,621; p=0,057).

Conclusion: IT had a considerable prevalence in our cohort. Patients often perceived it as highly disturbing, as much as the visible tremor. In our series, IT was correlated of anxiety symptoms but did not correlate with objective measures of generalized anxiety disorder. Internal tremor was not specific feature of ET or PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/internal-tremor-in-parkinson-disease-and-essential-tremor-a-new-glance-at-a-common-symptom/