Exploring the effect of electrical muscle stimulation as a novel treatment of intractable tremor in Parkinson's disease

Background: As the pathophysiology of tremor in Parkinson disease (PD) involves a complex interaction between central and peripheral mechanisms, we propose that modulation of peripheral reflex mechanism by electrical muscle stimulation (EMS) may improve tremor temporarily. Objectives: To determine the efficacy of EMS as a treatment for drug resistant tremor in PD patients. Methods: This study was a single-blinded, quasi-experimental study involving 34 PD patients with classic resting tremor as confirmed by tremor analysis. The EMS was given at 50 Hz over the abductor pollicis brevis and interrosseus muscles for 10 s with identified tremor parameters before and during stimulation as primary outcomes. Results: Compared to before stimulation, we observed a significant reduction in the root mean square (RMS) of the angular velocity (p < 0.001) and peak magnitude (p < 0.001) of resting tremor while tremor frequency (p = 0.126) and dispersion (p = 0284) remained unchanged during stimulation. The UPDRS tremor score decreased from 10.59 (SD = 1.74) before stimulation to 8.85 (SD = 2.19) during stimulation (p < 0.001). The average percentage of improvement of the peak magnitude and RMS angular velocity was 49.57% (SD = 38.89) and 43.81% (SD = 33.15) respectively. 70.6% and 61.8% of patients experienced at least 30% tremor attenuation as calculated from the peak magnitude and RMS angular velocity respectively. Conclusions: Our study demonstrated the efficacy of EMS in temporarily improving resting tremor in medically intractable PD patients. Although tremor severity decreased, they were not completely eliminated and continued with a similar frequency, thus demonstrating the role of peripheral reflex mechanism in the modulation of tremor, but not as a generator. EMS should be further explored as a possible therapeutic intervention for tremor in PD. (C) 2015 Elsevier B.V. All rights reserved.