Orthostatic Tremor during Modification of Stance

Introduction: The primary orthostatic tremor (OT) is a fast tremor occurring only in the standing position. We have now studied whether OT is influenced by modification of the condition „stance“. Patients and Methods: We investigated 7 patients with primary OT (age 46–77 years, median 68 years). All patients revealed a 14–18/s tremor in the muscles of both legs during standing. The tremor activity was analyzed under different conditions: 1) Relief of the body weight to 75%, 50%, 25% and 0% (complete relief of the body weight, the patient's feet still touched the bottom) by vertical elevation of the patient. 2) Relief by a tilting table with the positions 90° (upright stance), 80°, 45° and 0° (horizontal position, the feet still touched the base). OT was measured with surface EMG (4 traces) from the muscles of both legs. Results: In all patients, there was a clear OT activity during all conditions, even at complete relief of the body weight or, respectively, in the horizontal position with the tilting table. The tremor frequencies at the different conditions were not significantly different (ANOVA, p>0.05). Conclusion: Modifications of the condition „stance“ as tested in this study were not sufficient to suppress OT generation. Our data suggest that the body weight plays a less important role in OT generation.