Objective: To examine whether features described in tapping test are specific to functional tremor by evaluating rest and postural tremor in PDpatients using the same protocol for assessment of functional tremor.

Background: Electrophysiological tests such as the tapping test are used to distinguish functional and non-functional tremors.

Patients with functional tremor commonly show entrainment, frequency shift of the tremor of more than 1.5 Hz, and amplitude reduction (>50% decrease relative to baseline) during tapping of the contralateral hand.Tremor in Parkinson’s disease is known to increase in amplitude during cognitive tasks and have spontaneous fluctuations. However, the tapping test has not been tested in Parkinson’s disease (PD) tremor.

Method: We evaluated 20 PD patients (3F, age 64.9±7.6[mean±SD] years) with rest and postural tremor and without clinical diagnosis of functional tremor component using surface electromyography and triaxial accelerometry. The tremor was evaluated in the moreaffected arm at rest and with arms outstretched. Tremorswere recorded while tapping at 1, 3 and 5 Hz with the contralateral arm paced by a metronome. Tremor amplitude and frequency were calculated using the average from power spectrum analysis of the three axesfrom accelerometer recordings, and tapping and no taping conditions were compared. The accuracy of the tapping was also measured.

Results: Rest tremor showed reduction of amplitude in 4 patients while tapping at 1 Hz and in 3 patients while tapping at3Hz with the contralateral hand. Moreover, rest tremorshowed entrainment in 4 patients while tapping at 3Hz. Postural tremor was suppressed in 3 patients while tapping at 1 Hz and 1 patient with 3Hz taping. There was entrainment with frequency shift in 2 patients while tapping at 3 Hz. Nineteen patients had an increase in amplitude of rest tremor while tapping at 5 Hz, the same happened in 10 patients with postural tremor.

Conclusion: Distractibility and entrainment can be found in PD tremor and is more common in rest tremor than postural tremor. The tapping test at 1 and 3 Hz may not reliably distinguish between PD tremor and functional tremor.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/parkinsons-disease-tremor-can-show-entrainment-and-distractibility-with-electrophysiological-assessment-using-tapping-test/