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

Rigby HB, Rigby MH, Caviness JN - Tremor Other Hyperkinet Mov (N Y) (2015)

Bottom Line: Lower frequency discharges tended to have a broader spectral peak, greater variability in discharge duration, and lower inter-muscular coherence.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.These subjects may have greater gait involvement and higher likelihood of falls leading to earlier presentation to subspecialty care.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Movement Disorders Center, Mayo Clinic, Scottsdale, AZ, USA ; Division of Neurology, Dalhousie University, Halifax, NS, Canada.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus

Histogram Analysis Showing the Distribution of Dominant Tremor Frequencies.
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Figure 0001: Histogram Analysis Showing the Distribution of Dominant Tremor Frequencies.

Mentions: Demographic and clinical features were collected from the charts. The Neuroscan System (Compumedics Neuroscan, Charlotte, NC, USA) was used to collect neurophysiologic data on all subjects. Surface EMG recordings were collected at 1,000 Hz (1–200 Hz bandpass) with the patient sitting comfortably in a chair, during postural activation with wrist extension and/or arms outstretched, during various functional maneuvers (finger-to-nose testing, handwriting), standing, and in some cases leaning against an object from a standing position. Neurophysiologic information was extracted from the neurophysiology reports and from systematic analysis of the stored EMG data. The predominant frequency of tremor was determined by spectral analysis and confirmed to be consistent with visual inspection of the number of bursts per second in all cases. The lower frequency OT group (<13 Hz) was subdivided into two groups, intermediate (10–13 Hz) and low frequency (<10Hz), based on clustering seen on the histogram analysis (Figure 1).


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

Rigby HB, Rigby MH, Caviness JN - Tremor Other Hyperkinet Mov (N Y) (2015)

Histogram Analysis Showing the Distribution of Dominant Tremor Frequencies.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4548762&req=5

Figure 0001: Histogram Analysis Showing the Distribution of Dominant Tremor Frequencies.
Mentions: Demographic and clinical features were collected from the charts. The Neuroscan System (Compumedics Neuroscan, Charlotte, NC, USA) was used to collect neurophysiologic data on all subjects. Surface EMG recordings were collected at 1,000 Hz (1–200 Hz bandpass) with the patient sitting comfortably in a chair, during postural activation with wrist extension and/or arms outstretched, during various functional maneuvers (finger-to-nose testing, handwriting), standing, and in some cases leaning against an object from a standing position. Neurophysiologic information was extracted from the neurophysiology reports and from systematic analysis of the stored EMG data. The predominant frequency of tremor was determined by spectral analysis and confirmed to be consistent with visual inspection of the number of bursts per second in all cases. The lower frequency OT group (<13 Hz) was subdivided into two groups, intermediate (10–13 Hz) and low frequency (<10Hz), based on clustering seen on the histogram analysis (Figure 1).

Bottom Line: Lower frequency discharges tended to have a broader spectral peak, greater variability in discharge duration, and lower inter-muscular coherence.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.These subjects may have greater gait involvement and higher likelihood of falls leading to earlier presentation to subspecialty care.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Movement Disorders Center, Mayo Clinic, Scottsdale, AZ, USA ; Division of Neurology, Dalhousie University, Halifax, NS, Canada.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus