Table 2.

Electrophysiological characteristics of hyperkinetic syndromes.

Essential tremor (Bhatia et al., 2018, Vial et al., 2019)a

•Bilateral upper limb tremor •Frequency 4–12  Hz with a bilateral central component •Frequency reduced by 1 Hz or less during weight-loading •Non-significant coherence between right and left hands

Enhanced physiological tremor (Hallett, 2008; Vial et al., 2019)

•Bilateral upper limb tremor with frequency 4 to 12 Hz with an associated EMG spectral peak that is coherent with the mechanical resonant oscillation •Frequency reduces by greater than 1 Hz during weight-loading

Parkinsonian tremor (Vial et al., 2019)

•Rest tremor with 4–7 Hz frequency •Re-emergence during posture

Functional tremor (Schwingenschuh et al., 2011, Schwingenschuh et al., 2016)

At least three of the following are present: •Tremor paused or decreased in amplitude by half during contralateral ballistic maneuvers •Significant coherence, as defined by two contiguous bins on the coherence plot that rose above the 99 % confidence limit for random coherence at a frequency where there were corresponding peaks in the power spectra •Entrainment or tremor suppression during tapping •Abnormal tapping performance during entrainment

Dystonic tremor (Bhatia et al., 2018; Chen and Chen, 2020)

•Tremor syndrome combining tremor and dystonia as the leading neurological signs •Co-contractions of agonist and antagonist muscles

Task-specific or position-specific tremor

•Tremor signal quantifiable with a reproducible peak in accelerometry and/or EMG spectra during a specific position or task

Holmes tremor (Deuschl et al., 2022; Milanov, 2002, Miwa et al., 1996)

•Frequency 2.5–5 Hz •Large amplitude tremor present at rest, during posture, and kinesis •Proximal and distal rhythmic muscle contractions •EMG burst durations of 150–170 ms with an alternating activation pattern of agonist and antagonist muscles

Orthostatic tremor (OT) (Sander et al., 1998, Vial et al., 2019)

Classical OT •Bilateral leg tremor when standing with frequency between 13–18  Hz •Significant coherence between right and left legs as defined by two contiguous bins on the coherence plot that rose above the 99 % confidence limit for random coherence at a frequency where there were corresponding peaks in the power spectra Slow OT •Bilateral leg tremor when standing with frequency less than 13 Hz •Coherence between legs may or may not be significant

Myoclonus (Merchant et al., 2020)

•EMG muscle burst duration ≤ 100 ms

Orthostatic myoclonus (Hassan and Van Gerpen, 2016)

•EMG muscle burst duration ≤ 100 ms in the legs when standing

Note: This table includes the various hyperkinetic syndromes observed in our cohort.

^aPer current understanding, the criteria for essential tremor are also applicable to essential tremor plus.