Objective: To review all published cases of Orthostatic Tremor (OT), and summarize available clinical data and knowledge gaps.

Background: OT is a rare disorder of stance, characterized by unsteadiness and a fast tremor (typically 13-18 Hz). Both symptoms improve by walking and leaning, and resolve upon sitting and lying supine. The multitude of case reports has provided conflicting data, and few retrospective case series have left many questions unanswered.

Methods: We reviewed all new OT cases reported in PubMed (search terms: orthostatic tremor, shaky leg, primary orthostatic tremor) before October 2015. Reviews of previously reported cases, OT mimics, pseudo OT and Orthostatic Myoclonus cases were excluded, yielding 78 publications.

Results: The search produced 434 cases (96% EMG-confirmed). Many historical details were missing in these reports. Mean age of onset was 56.3 years (n=227), with a range of 7 to 87 years. Female to male ratio was 1.9:1 (n=425). Duration of the disease at diagnosis ranged from months to 40 years (average 9.8 years, n=244). Although main symptom was unsteadiness, 74 % of patients denied falls, and 14% reported rare falls (n=105). Disease progression was seen in 78% of the cases when reported (n=123). Non-OT tremor was present in 35% (151/434); mostly slow postural hand tremor (92/151, 61%). Familial OT has been suspected in 15 cases. The Surface EMG data available showed mean OT frequency of 15.4 Hz (n=163) and most (114/163, 70%) were between 14-16 Hz. On EMG, latency to onset of tremor after standing can vary from 200 milliseconds to 15 seconds. Limitations on activities daily living and QOL impairment was strongly suspected but data is very scarce. We found only three randomized controlled drug trials (Leviteracetam and Gabapentin). However most commonly prescribed medication was Clonazepam. In four large retrospective case series of OT (n=100), response to Clonazepam was about 30% and only half of the patients had a sustained response over time. Six OT patients had successful Deep Brain Stimulation Surgery (maximum follow-up = 1 year).

Conclusions: Due to the retrospective, non-uniform nature of the data, there are significant knowledge gaps in the natural history, presentation, physical exam, functional limitations and treatment of OT patients. Prospectively-collected data could help guide future research in this rare disorder.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/orthostatic-tremor-a-literature-review-of-clinical-data/