Objective: To examine the clinical and electrophysiologic characteristics of patients with mixed functional and organic tremor.

Background: Functional tremor is one of the most common movement disorders and can lead to significant impairment and healthcare cost. Prior studies have demonstrated that neurophysiologic evaluation of functional tremor can increase diagnostic sensitivity over clinical evaluations alone. However few studies have examined patients with mixed organic and functional tremor [1].

Method: Patients referred for upper limb surface EMG for tremor at the movement disorders lab at Mayo Clinic, Rochester were randomly sampled over 9 years and retrospectively reviewed. Surface EMG electrodes were placed on muscles of the upper limbs. Recording was performed per a set protocol examining rest, posture, action, positions and with distraction tasks such as tapping.

Results: Of 117 patients, 26 (median age 46 yrs, IQR 35-52) had functional tremor. 7 patients (median age 50, IQR 42-68) had a mixed functional and organic tremor. Out of these, 6 patients had an organic postural/action tremor and 1 patient had organic resting tremor plus functional tremor. In contrast, 91 patients with organic tremor were median age 57 (IQR 45-68). The median duration of tremor prior to diagnosis for functional tremor was 1.5 years (IQR 1-9), compared with organic tremor 3 years (IQR 1-15), and mixed organic and functional tremors was 11 years (IQR 2-15). Most patients (92%) with functional tremor had a variable frequency of tremor (>3 hz variability). 23 patients exhibited either a distractable or entrainable tremor. In patients with a mixed functional and organic postural/action tremor, the median frequency of the organic tremor was 6.5 Hz (IQR 6.0-7.4). The patient with mixed functional and organic resting tremor had an organic tremor frequency range between 4-6 Hz. The functional tremors demonstrated variable frequency of tremor. All organic tremors had a fixed frequency with tapping and did not distract or entrain. Two thirds (67%) of patients with functional and organic tremor underwent MRI during their workup, out of which none were found to change management.

Conclusion: Patients with mixed functional and organic tremor had a delay in diagnosis when compared to patients with functional tremor or organic tremor alone. Electrophysiology was required for diagnosis, and neuroimaging did not change management in these cases.

References: 1.Schwingenschuh P., Saifee T., Katschnig-Winter P., Macerollo A., Koegl-Wallner M., Culea V., Ghadery C., Hofer E., Pendl T., Seiler S., Werner U., Franthal S., Maurits N., Tijssen M., Schmit R., Rothwell J., Bhatia K., Edwards M. Validation of laboratory-supported criteria for functional (psychogenic) tremor. Mov Disord. 2016; 32(4): 555-62.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/utility-of-tremor-electrophysiology-studies-in-patients-with-mixed-functional-and-organic-tremor/