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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

Surface Electromyography Tracings and Spectral Analysis in Patients with High-, Intermediate-, and Low-Frequency Orthostatic Tremor.
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Figure 0002: Surface Electromyography Tracings and Spectral Analysis in Patients with High-, Intermediate-, and Low-Frequency Orthostatic Tremor.

Mentions: Those with classic orthostatic leg tremor (>13 Hz) had uniformly brief discharges based on visual inspection of individual surface EMG tracings (Figure 2). Cases with 10–13 Hz frequency tremor also had a high proportion of short-duration discharges whereas those in the <10 Hz group had longer-duration discharges with a low proportion of short-duration discharges. The variability in EMG burst interval duration also differed between groups as calculated by the mean spectral peak width at half of the peak amplitude. This mean value was largest in the <10 Hz group and smallest in the >13 Hz group (mean 1.51, 1.00, and 0.66 Hz) with a statistically significant difference between each group using multiple comparisons with Tukey correction (all p<0.05) (Table 1). Clustering of subjects by tremor frequency is shown in Figure 3.


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)

Surface Electromyography Tracings and Spectral Analysis in Patients with High-, Intermediate-, and Low-Frequency Orthostatic Tremor.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 0002: Surface Electromyography Tracings and Spectral Analysis in Patients with High-, Intermediate-, and Low-Frequency Orthostatic Tremor.
Mentions: Those with classic orthostatic leg tremor (>13 Hz) had uniformly brief discharges based on visual inspection of individual surface EMG tracings (Figure 2). Cases with 10–13 Hz frequency tremor also had a high proportion of short-duration discharges whereas those in the <10 Hz group had longer-duration discharges with a low proportion of short-duration discharges. The variability in EMG burst interval duration also differed between groups as calculated by the mean spectral peak width at half of the peak amplitude. This mean value was largest in the <10 Hz group and smallest in the >13 Hz group (mean 1.51, 1.00, and 0.66 Hz) with a statistically significant difference between each group using multiple comparisons with Tukey correction (all p<0.05) (Table 1). Clustering of subjects by tremor frequency is shown in Figure 3.

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