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 or 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 the diagnosis requires confirmation with surface electromyography (SEMG). Recently applications using the accelometer feature of smartphones (SPA) have been used to detect and quantify tremors, including OT (1), though the accuracy of SPA in diagnosing OT is unknown.

We conducted a prospective pilot study of 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.  We assessed tremor using the StudyMyTremor application (2) on an iPhone 6s adhered with medical tape to the patient’s right tibialis anterior. SEMG was completed at the same site. The primary outcome of this study was to determine the SPA’s sensitivity and specificity in detecting OT (defined as a 13-18 Hz tremor) when compared with SEMG.