Utility of tremor electrophysiology studies

Abstract

Objective: To determine the utility of tremor electrophysiology testing in differentiating clinically indeterminate tremor due to organic, functional, and mixed tremor types.

Background: Prior studies have shown that electrophysiological studies increase diagnostic sensitivity of tremor syndromes; however, few have examined mixed organic and functional tremors.

Methods: Patients referred for tremor to the Mayo Clinic, Rochester movement disorders lab were consecutively selected and retrospectively reviewed. Surface electromyography (EMG) recordings of upper limb muscles were performed at rest, posture, with action and distractibility tasks.

Results: Of 116 patients, all were clinically described as having either a resting tremor, postural tremor, action tremor, postural and action tremor, mixed resting, postural, and action tremor, or nonspecific tremulousness. Based on electrophysiological features, patients were diagnosed with organic tremor (parkinsonian, essential, mixed, rubral, cerebellar, non-specific tremulousness), functional tremor, or mixed functional and organic tremors. The median disease duration at electrophysiological confirmation of diagnosis was shorter for functional tremor at 1.5 years (IQR 1-9.3), and organic tremor at 3 years (IQR 1-15), versus mixed organic and functional tremor at 11 years (IQR 2-15) (p = 0.0422). The electrophysiology study clarified the referral/clinical diagnosis in 87 patients (75%), 26 (29.5%) of whom had functional tremor, and 61 (70.1%) had organic tremor or mixed organic/functional tremor. Variability of tremor during electrophysiology testing was associated with a change in diagnosis (p = 0.0286).

Conclusion: Our findings show that electrophysiological assessment of tremor can be helpful in the clinical diagnosis of patients with both organic and functional tremor.

Keywords: Distractibility; Electrophysiology; Entrainment; Functional tremor.

Fig. 1

Surface EMG of organic and functional tremor. A: Alternating rhythmic EMG bursts are recorded over the wrist extensor and flexor muscles. Rest or postural tremor may have a similar electrophysiologic appearance and will be characterized by limb position during recording. B: Patient performs finger tapping at pre-set frequencies with the left hand (LH). The tremor in the right hand (RH) becomes variable in frequency.

Fig. 2

Time frequency analysis of organic tremor: Organic tremor will have a fixed frequency that persists during contralateral finger tapping.