Abstract
Primary orthostatic tremor (OT) is characterized by high-frequency lower-limb muscle contractions and a disabling sense of unsteadiness while standing. Patients consistently report a relief of symptoms when starting to ambulate. Here, we systematically examined and linked tremor and gait characteristics in patients with OT. Tremor and gait features were examined in nine OT patients and controls on a pressure-sensitive treadmill for one minute of walking framed by two one-minute periods of standing. Tremor characteristics were assessed by time-frequency analysis of surface EMG-recordings from four leg muscles. High-frequency tremor during standing (15.29 ± 0.17 Hz) persisted while walking but was consistently reset to higher frequencies (16.34 ± 0.25 Hz; p < 0.001). Tremor intensity was phase-dependently modulated, being predominantly observable during stance phases (p < 0.001). Tremor intensity scaled with the force applied during stepping (p < 0.001) and was linked to specific gait alterations, i.e., wide base walking (p = 0.019) and increased stride-to-stride fluctuations (p = 0.002). OT during walking persists but is reset to higher frequencies, indicating the involvement of supraspinal locomotor centers in the generation of OT rhythm. Tremor intensity is modulated during the gait cycle, pointing at specific pathways mediating the peripheral manifestation of OT. Finally, OT during walking is linked to gait alterations resembling a cerebellar and/or sensory ataxic gait disorder.
Highlights
Primary orthostatic tremor (OT) is a unique clinical syndrome of unknown prevalence, characterized by a high-frequency pattern of coherent muscle contractions (13–18 Hz) in the lower limbs and trunk while standing[1,2,3]
We studied tremor activity during stance-walk transitions and continuous walking as well as gait performance in patients with OT
The main three findings were: (1) coherent high-frequency tremor bursts persist during walking but are shifted to a higher frequency range; (2) tremor intensity during walking is phase-dependently modulated and scales with the leg force levels applied during stepping; (3) intense tremor activity during walking is associated to specific gait alterations
Summary
Primary orthostatic tremor (OT) is a unique clinical syndrome of unknown prevalence, characterized by a high-frequency pattern of coherent muscle contractions (13–18 Hz) in the lower limbs and trunk while standing[1,2,3]. Anecdotal reports in single patients with OT indicate that tremor activity may persist during walking[3,7,8] It is hitherto unknown whether the ongoing tremor activity during ambulation is akin to that of standing or may exhibit specific changes with respect to frequency, intensity or coherence. It is further unclear whether OT during walking is linked to a specific gait disorder as observed in other types of tremor such as essential tremor[9] It has to be resolved, why despite continuation of OT during walking, most patients consistently experience a substantial relief of subjective unsteadiness associated with activity. These findings were linked to the walking performance of patients by simultaneous recordings of their spatiotemporal gait patterns
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