Orthostatic tremor and its subtypes: a single centre cohort of 74 patients

BACKGROUND: Orthostatic tremor (OT) is a rare, heterogenous disorder, recently sub-classified into primary OT (isolated 13-18 Hz tremor), OT-plus (OT with additional neurological features) and pseudo-OT (OT with frequencies < 13 Hz). However, to our knowledge no study to date has compared clinical characteristics between all three subgroups. OBJECTIVES: We aim to further define and compare the clinical characteristics of the three different OT subgroups, utilising one of the largest described single centre cohorts to date. METHODS: A retrospective analysis was undertaken of clinical records from 74 OT patients at Charing Cross Hospital between 1999 and 2023, enabling categorisation into subgroups. Clinical characteristics, including treatment efficacy and overall disability, were subsequently described and compared between subgroups. RESULTS: 61 primary OT, 5 OT-plus and 8 pseudo-OT patients were identified. Baseline demographics were comparable between subgroups. Logistic regression suggested age of onset (OR = 1.02, p = 0.229), symptom duration (OR = 1.05, p = 0.083), tremor frequency (OR = 1.02, p = 0.826) and subgroup (OT-plus (OR = 1.86, p = 0.565) and pseudo-OT (OR = 1.41, p = 0.683)) were not significant predictors of disability. Treatment response varied between subgroup, with primary OT and pseudo-OT patients more frequently reporting symptomatic improvement with clonazepam, gabapentin and/or alprazolam than OT-plus patients. CONCLUSIONS: We provide further insight into the clinical phenotypes of the OT subgroups and encourage future studies to validate these findings with larger sample sizes and establish reliable tools to measure OT severity to better assess disease progression and treatment response.