Objective: To clarify the characteristics of leg tremors in cases with primary orthostatic tremor (OT) and Parkinson’s disease (PD) using surface electromyography (SEMG) with modifications of the standing condition.

Background: OT is a rare disorder characterized by leg tremor and subjective unsteadiness only on standing still but absent when sitting or lying, improved by walking or leaning. Although rare, some PD cases can also present with leg tremors on standing. Those tremors have distinctive frequency bands, 13-18 Hz for OT and 4-9 Hz for PD, determined by SEMG. Subjective unsteadiness is one of the striking characteristics in OT and patients with OT tend to avoid situations like queuing and try to lean against a wall, whereas patients with PD do not usually complain such strong unsteadiness. We performed SEMG on leg muscles in a case with OT and another case with PD with variable conditions of standing to determine if leg tremors are influenced by such modifications.

Methods: Frequencies of leg tremors were determined by SEMG on leg muscles in cases with OT and PD diagnosed according to the diagnostic criteria for each disorder. SEMG were also performed with modifications of the standing condition such as standing with different stance widths, with a cane and with leaning. Data of SEMG were analyzed and compared with different conditions and between OT and PD cases.

Results: The tremor discharges were found in her both legs of a female case with OT in her fifties and in his right leg of a male PD case in his fifties on standing by SEMG. The frequencies were determined to be approximately 15 Hz for the OT case and 5 Hz for the PD case. The changes of amplitudes of muscle discharges in accordance with the modifications were similar in both cases; the amplitudes were highest with their feet placed together and decreased with widening their stance and with using their canes, and the discharges almost disappeared with leaning, however, the amplitudes were higher throughout in the OT case. The result suggested that the higher frequencies and amplitudes of tremor discharges and the involvement of both legs in the OT case might be associated with the unsteadiness on standing.

Conclusions: The leg tremors changed similarly with modifications of the standing condition in both OT and PD cases, however, the frequencies and amplitudes were higher in the OT case with both legs involved. These differences might be associated with the unsteadiness on standing, which is the most prominent clinical feature of OT. These data are also presented at the 12th Congress of the Movement Disorder Society of Japan on July 5-7, 2018.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/characteristics-of-leg-tremors-on-standing-in-primary-orthostatic-tremor-and-parkinsons-disease/