Internal tremor in people with Parkinson’s Disease: Demographic characteristics and comorbid symptoms

INTRODUCTION: Internal tremor (IT) occurs in > 30 % of people with Parkinson’s Disease (PwPD), but remains largely uninvestigated. Our objective was to describe demographic characteristics and associated symptoms in PwPD who reported IT. METHODS: This was a matched case-control survey study. Data were from PwPD in the Fox Insight study who answered the Patient Report of Problems (PD-PROP) assessment, a series of open-ended questions that asks people to report in their own words their most bothersome PD-related problems. Cases were those who reported IT ≥ 1 times compared with PwPD controls who did not report IT and were matched 1:3 by age and disease duration. RESULTS: 243 PwPD reported IT as a bothersome problem. Mean (SD) age of cases was 64.9 (9.4) years and disease duration was 3.8 (4.0) years. The proportion of women was greater among cases compared to controls (74 % vs 47 %, p < 0.0001). External tremor as a PD-PROP symptom was reported by 98 % cases and 48 % controls (p < 0.0001). Several non-motor symptoms were more common among cases than controls, including anxiety (35 % vs 20 %), fatigue (41 % vs 31 %), and pain (57 % vs 37 %). The odds of IT was significantly higher in women when adjusting for anxiety and motor experiences of daily living score (OR 3.07, 95 %CI 2.14–4.41, p < 0.0001). CONCLUSION: PwPD with IT report a range of associated symptoms, including external tremor, anxiety, and pain. Sex differences in the experience of IT may exist. Studies of IT are needed to understand its etiology and inform clinical care.