Effects of transcutaneous electrical nerve stimulation on motor cortex excitability in writer's cramp: neurophysiological and clinical correlations.

We recently reported that transcutaneous electrical nerve stimulation (TENS) applied over forearm flexor muscles, a paradigm producing in physiological conditions transient changes in corticomotoneuronal excitability of forearm muscles, may improve motor symptoms in writer's cramp (WC). In the present study, we explored the possibility that one or repeated sessions of TENS might have beneficial effects on handwriting in WC by remodulating cortical excitability of forearm agonist and antagonist muscles. Motor evoked potentials (MEPs) after transcranial magnetic stimulation of the left motor cortex were recorded from the right flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles, before and after 1 and 15 sessions of TENS applied over flexor muscles in patients and in a control group. One session of TENS induced a significant smaller reduction of MEPs from the FCR and a smaller increase of the MEPs from the ECR in patients than in normal subjects. In WC, repeated sessions of TENS had the effect to decrease MEP amplitude in the FCR and to increase it in the ECR. This modulation was paralleled by a handwriting improvement. In conclusion, repeated TENS sessions may have the effect to re-modulate excitability of the motor cortex in WC and this modulation might partially play a role in temporarily improving the handwriting.