Posturography Can Be Used to Screen for Primary Orthostatic Tremor, a Rare Cause of Dizziness

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Abstract
Primary orthostatic tremor is a rare neurologic condition of unknown origin characterized by a 10- to 20-Hz tremor in the legs while standing. Patients with primary orthostatic tremor usually complain of dizziness and unsteadiness that is relieved if they sit down or start to walk around. These patients might be referred to neurotology clinics. Previously, the only way to make the diagnosis has been by means of surface electromyographic recordings from the lower limbs during standing. The authors wanted to study whether posturography can be used to screen for primary orthostatic tremor. Retrospective case review. Balance clinic at a tertiary referral center. From September 2000 to August 2002, 701 patients were investigated at the authors' balance clinic. Static posturography on a force platform with 50-Hz sampling frequency. Recordings were made during 120 seconds of quiescent stance with open or closed eyes. Fast-Fourier transformation (FFT) analysis of recorded torque in the fore-to-aft direction to quantify the spectral power distribution in the range of 0 to 25 Hz. Visual inspection of power spectrum plots was performed. Five patients (0.7%) were identified (1 man and 4 women; mean age, 56 yr; age range, 36-73 yr) with narrow peaks at 8.5 to 18 Hz in the power spectra of their posturographic recordings. Surface electromyographic recordings during standing confirmed their diagnosis of primary orthostatic tremor. Analysis of power spectra from posturographic recordings is a simple, quick method to screen for primary orthostatic tremor. The condition might be more common than previously assumed. It is important to identify patients with primary orthostatic tremor because they might be misdiagnosed and left without treatment.