Orthostatic Tremor Is Evoked by Muscle Load Without the Need for Orthostatic Position

Area of Science:

• Neurology
• Movement Disorders

Background:

• Primary orthostatic tremor (POT) is a rare movement disorder causing high-frequency tremor and unsteadiness, significantly impacting daily life.
• The tremor typically occurs in the standing position and affects the lower extremities, but its necessity for an orthostatic position was unclear.

Purpose of the Study:

• To investigate the response of primary orthostatic tremor (POT) to muscle load in non-orthostatic positions.
• To determine if an orthostatic position is essential for POT manifestation.

Main Methods:

• Tremor analysis in POT patients using a smartphone application attached to the proximal fibula.
• Measurements were taken in supine, seated, and standing positions.
• Tremor was also assessed during seated leg press exercise with applied muscle load.

Main Results:

• The tremor of POT can be elicited by muscle load in a seated position, indicating a weight-bearing isometric tremor.
• The amplitude of the elicited tremor is modulated by the load's weight, but the frequency remains unaffected.
• These findings challenge the necessity of a standing position for POT manifestation.

Conclusions:

• Primary orthostatic tremor (POT) appears to be a weight-bearing hyperkinetic disorder.
• The study challenges the conventional view that POT requires a standing position to fully manifest.
• Results have implications for understanding POT mechanisms and future research, such as MRI studies.