TENS is harmful in primary writing tremor

Objective: It is unclear whether primary writing tremor (PWT) is a tremulous form of dystonia or a tremor per se. Transcutaneous electrical nerve stimulation (TENS) at 50 Hz applied for 2 weeks was reported to improve the writing capabilities of patients with writer's cramp (WC). We explored whether such a beneficial effect can be obtained in patients with a PWT. Methods: In a cross-over, double-blinded randomized study we tested whether 2-week periods of 5, 25 or 50 Hz TENS applied to wrist flexor muscles, improved the score of the Fahn-Tolosa-Marin scale of nine patients with PWT. Excitability of neurons and of various intracortical circuits in the motor cortex were also tested before and after TENS by using transcranial magnetic stimulation. Results: TENS at 5 and 25 Hz did not have any effect while TENS at 50 Hz worsened the clinical condition and the cortical excitability. Conclusions: TENS is not a new treatment alternative for PWT. Significance: The beneficial effect in WC and the harmful one in PWT of TENS stresses that the two disorders are likely different nosological entities. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.