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Orthostatic Tremor: A Spectrum of Fast and Slow Frequencies or Distinct Entities?

Rigby, Heather B.; Rigby, Matthew H.; Caviness, John N.

Background: Orthostatic tremor (OT) is defined by the presence of a high-frequency (13–18 Hz) tremor of the legs upon standing associated with a feeling of unsteadiness. However, some patients have discharge frequencies of <13 Hz, so-called “slow OT”. The aim of this study was to characterize patients with unsteadiness upon standing found to have <13 Hz tremor discharges on neurophysiologic testing.

Methods: A retrospective review was performed on all subjects with a diagnosis of OT who were referred to the Mayo Clinic, Scottsdale, AZ, between 1999 and 2013 for confirmation using neurophysiology.

Results: Fourteen of 28 subjects (50%) had OT discharges of <13 Hz, of whom eight had frequencies of <10 Hz and six had frequencies of 10–13 Hz. Lower frequency discharges tended to have a broader spectral peak, greater variability in discharge duration, and lower inter-muscular coherence. Subjects with <13 Hz OT had shorter mean disease duration at time of neurophysiology testing (2.00 years in <10 Hz group, 7.96 years 10–13 Hz group, and 11.43 years >13 Hz; p = 0.002). The proportion of subjects who experienced gait unsteadiness (85.7% vs. 66.6% vs. 21.4%; p = 0.016), falls (37.5% vs. 50% vs. 0%; p = 0.010), and had abnormal gait on examination (71.4% vs. 66.0% vs. 14.3%; p = 0.017) was greater in those with low and intermediate frequencies.

Discussion: Slow tremor electromyography frequencies (<13 Hz) may characterize a substantial proportion of patients labeled as OT. These subjects may have greater gait involvement and higher likelihood of falls leading to earlier presentation to subspecialty care.


Also Published In

Tremor and Other Hyperkinetic Movements

More About This Work

Academic Units
Center for Parkinson's Disease and Other Movement Disorders
Published Here
October 15, 2015