Objective: To clarify the characteristics of arm tremors in a case with primary orthostatic tremor (OT) using surface electromyography (SEMG) with modifications of recording conditions.

Background: OT is characterized by leg tremor with the distinctive frequency range of 13-18 Hz and subjective unsteadiness only on standing still but absent when sitting or lying, improved by walking or leaning. In OT cases, tremors like essential tremor (ET) of the outstretched arms are reported to be commonly observed. We conducted this study to clarify the characteristics of arm tremors in OT.

Method: Neurological examination was done and the frequency of arm tremors were determined using accelerometer in a female case with OT in her fifties. SEMG were performed in her arm and leg muscles with various conditions of her arms such as relaxed, outstretched, with voluntary muscle contraction and in weight bearing in both standing and sitting positions.

Results: Neurological examination revealed fine postural tremor of her outstretched arms with the frequency of approximately 8 Hz determined by accelerometer. No muscle discharges were observed in either her arms or legs when sitting with her arms relaxed. The muscle discharges with the frequency of around 15 Hz appeared in her arms and legs on standing with her arms relaxed. When her arms were outstretched, the muscle discharges with the frequencies of 15 Hz were detected in both her arms and legs on standing and those of 14-15 Hz appeared only in her arms on sitting. With voluntary contraction of her arm muscles, the muscle discharges with the frequencies of 15 Hz were seen in both her arms and legs on standing and those of 10-12 Hz appeared only in her arms on sitting. When her arms were in weight bearing condition on standing, the muscle discharges with the frequency of 10-15 Hz appeared in her arms, with the amplitudes of muscle discharges of her legs decreased or disappeared.

Conclusion: The arm tremors of our OT case had the frequency consistent with ET as previously reported, however, the muscle discharges with the frequencies within the range of OT or a little slower were demonstrated using SEMG with her arms outstretched, with voluntary contraction of her arm muscles, and when her arms and/or legs were in weight bearing conditions. These data are also presented at the 13th Congress of the Movement Disorder Society of Japan on July 25-27, 2019.

« Back to 2019 International Congress

MDS Abstracts - https://www.mdsabstracts.org/abstract/characteristics-of-arm-tremors-in-primary-orthostatic-tremor/