Objective: To demonstrate the usefulness of electronic stethoscope (ES) in making diagnosis of orthostatic tremor (OT).

Background: OT is a rare disorder first reported in the English literature by Heilman in 1984 and characterized by leg tremor and subjective unsteadiness only on standing, absent when sitting or lying, and improved by walking or leaning. The tremor cannot be reliably seen or palpated (1), and the diagnosis can be confirmed only by electromyography (EMG) recordings with a typical 13-18 Hz pattern (2). In 1995, Brown reported a new clinical sign for OT. It is a sound similar to the noise of a distant helicopter heard with a stethoscope (1). Recently, several models of ES have become commercially available and the recorded sound of auscultation can be transferred to a PC and immediately visualized. It would be useful if the diagnosis of OT could be confirmed by the findings of ES, especially in institutions where surface EMG is not easily available.

Methods: In a case with confirmed OT, the sound of leg muscles was recorded by ES (3M™ Littmann® Electronic Stethoscope Model 3200, 3M). The audio files were transferred via Bluetooth® to a PC (MacBook Pro®, Apple Inc.) and visualized by 3M™ Littmann® Stethassist™ software for analysis. The frequency and waveform of the muscle sound were compared with those of surface EMG of the same case.

Results: A female in her fifth decade noticed tremor in her left hand and both legs and unsteadiness when waiting in a queue 7 years before. Her symptoms appeared only when standing still, alleviated on leaning, and disappeared on walking. On examination, postural tremor was found in her arms, and the fine tremor in leg muscles was visible and palpable on standing with intermittent myoclonic movement. The ‘helicopter sign’ was heard by auscultation. Surface EMG revealed 16 Hz discharges and the diagnosis of OT was confirmed. Clonazepam was effective and the frequency of surface EMG was reduced to about 14 Hz. The sound of leg muscles recorded by ES was visualized and its frequency of the waveform was determined to be about 14 Hz.

Conclusions: The findings of unique ‘helicopter sign’ for OT recorded and visualized using ES and analyzing software become comparable with those of surface EMG. Their frequencies are considered to be identical, which suggests that the diagnosis of OT may be confirmed by ES instead of surface EMG.

References: 1. Brown P. New clinical sign for orthostatic tremor. Lancet 1995;346:306-307.

2. Deuschl G, Bain P, Brin M, and an Ad Hoc Scientific Committee. Consensus statement of the Movement Disorder Society on Tremor. Mov Disord 1998;13(Suppl 3):2-23

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MDS Abstracts - https://www.mdsabstracts.org/abstract/electronic-stethoscope-in-the-diagnosis-of-orthostatic-tremor/