Abstract
BackgroundPrimary orthostatic tremor (OT) is a rare movement disorder characterized by a 13–18 Hz leg tremor, which arises when standing and is relieved by walking/sitting. Those affected generally do not fall, but experience fear of falling, lessened by ambulation. Because of its low amplitude, the tremor is not readily visible, and diagnosis requires confirmation with surface electromyography (sEMG). Recently, applications using the accelerometer feature of smartphones have been used to detect and quantify tremors, including OT, though the accuracy of smartphone accelerometry (SPA) in diagnosing OT is unknown.MethodsWe completed SPA in consecutive adults (18+ years), who presented to our neurology clinic with either subjective leg shakiness upon standing or unsteadiness when standing that lessened with ambulation, which comprised 59 of 2578 patients. We assessed tremor using the StudyMyTremor application on an iPhone 6 s adhered with tape to the patient’s tibialis anterior. Surface electromyography was completed on the same muscle. The primary outcome of this study was to determine SPA’s sensitivity and specificity in detecting OT compared with surface electromyography.ResultsFifty-nine patients with the following diagnoses were included: OT (6), Parkinson’s disease, Hereditary Spastic Paraplegia, orthostatic hypotension, essential tremor, spinal cerebellar ataxia, sensory ataxia and functional movement disorder. Smartphone accelerometry detected a 13–18 Hz tremor in 5 of 6 patients diagnosed with OT by sEMG with no false positives in other conditions, yielding a sensitivity of 83%, specificity of 100% in the cohort we studied.ConclusionsThough a larger sample size is desirable, preliminary data suggest that smartphone accelerometry is an alternative to surface electromyography in diagnosing OT.
Highlights
Primary orthostatic tremor (OT) is a rare movement disorder characterized by a 13–18 Hz leg tremor, which arises when standing and is relieved by walking/sitting
Orthostatic tremor (OT) is a rare movement disorder characterized by a low amplitude, high frequency (13– 18 Hz) leg tremor which arises when standing, improves with walking, and remits rapidly when lying or sitting
A diagnosis of OT should be suspected in any patient whose unsteadiness improves with walking; the tremor often cannot be visualized because of its low amplitude, and confirmation of the diagnosis requires electrophysiological testing to determine tremor frequency, such as surface electromyography
Summary
Primary orthostatic tremor (OT) is a rare movement disorder characterized by a 13–18 Hz leg tremor, which arises when standing and is relieved by walking/sitting. Orthostatic tremor (OT) is a rare movement disorder characterized by a low amplitude, high frequency (13– 18 Hz) leg tremor which arises when standing, improves with walking, and remits rapidly when lying or sitting. Those affected experience unsteadiness when standing and associated fear of falling, but rarely fall. A diagnosis of OT should be suspected in any patient whose unsteadiness improves with walking; the tremor often cannot be visualized because of its low amplitude, and confirmation of the diagnosis requires electrophysiological testing to determine tremor frequency, such as surface electromyography (sEMG). We assessed the sensitivity and specificity of SPAs in detecting OT, when compared with sEMG, with the goal of facilitating diagnostic options for the primary care provider
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