Objective: To describe a possible additional method to differentiate functional tremor (FT) from organic tremor (OT).

Background: Functional tremor is the most common manifestation of functional movement disorders. In 2009 Gupta and Lang have proposed to add neurophysiological studies in functional movement disorders criteria [1]. In 2011 Tremor Test Battery has also been elaborated to objectify the functional nature of tremor, which consists of a tapping task, 500-g mass loading, and ballistic hand movement [2]. In 2020 a new software Tremoroton was released for tremor analysis [3].

Method: The study included 12 patients with FT (8 females, mean age 42.5 years) and 8 patients with ОТ (5 females, mean age 47.6 years; 4 patients were diagnosed with Parkinson’s disease, 2 with Wilson’s disease, one with essential tremor, and one had neurodegeneration with brain iron accumulation). Two-channel accelerometry and four-channel EMG (flexor and extensor muscles) of both arms were performed. The recording was carried out at rest, posture with outstretched arms without and with a cognitive load. Recorded signals were further processed by the Tremoroton. The stability of peak frequencies of accelerometer oscillations and EMG activity were evaluated using density compressed spectral array (DSCA) in a 30-second recording.

Results: The cognitive load led to increased instability of peak frequencies in 9 patients with FT and in 1 patient with OT. The constancy of EMG activity of at least one muscle was observed in 7 OT cases and was not observed in patients with FT [figure 1].

Conclusion: Spectrogram (DSCA) can be fast and useful method to identify FT. But it requires further research and subsequent validation in comparison with Tremor Test Battery.

References: 1. Gupta A, Lang AE. Psychogenic movement disorders. Curr Opin Neurol. 2009;22(4):430-436. doi:10.1097/WCO.0b013e32832dc169
2. Schwingenschuh P, Katschnig P, Seiler S, et al. Moving toward “laboratory‐supported” criteria for psychogenic tremor. Movement Disorders. 2011;26(14):2509-2515. doi:10.1002/mds.23922
3. Vial F, McGurrin P, Osterholt T, Ehrlich D, Haubenberger D, Hallett M. Tremoroton, a new free online platform for tremor analysis. Clin Neurophysiol Pract. 2020;5:30-34. doi:10.1016/j.cnp.2019.11.004

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spectrogram-helps-to-differentiate-functional-tremor-from-organic/