tic disorders Treatment Tic Disorders blog Tics at WUSTL

Can median nerve stimulation reduce tics?

A fascinating publication from the University of Nottingham describes a non-invasive method that may reduce tics. The idea is that rhythmic input to a brain region can entrain that region to fire in synchrony with the input, and some rhythmic firing patterns seem to inhibit movement. The stimulation was delivered by generating a small electrical current at a frequency of 10-12 Hz to the skin over a nerve in the wrist (the median nerve). The electrical current is dialed down to just barely enough to make the thumb twitch.

The authors tested this new idea in two ways. First, they showed that brain activity in an area of the brain corresponding to sensation and movement could be synchronized with the electrical pulses at the wrist. The same number of randomly timed, non-rhythmic pulses did not produce the same effect.

Second, 19 volunteers with TS engaged in a 4-minute-long study in which 2 of the minutes included median nerve stimulation (MNS) and 2 minutes did not. The order of stimulation vs. no stimulation varied across participants. Six of the 19 people found the stimulation uncomfortable. The participants were video recorded during the 4 minutes, and a tic doctor who didn’t know when the stimulation was on or off counted tics and rated their severity for each of the 4 minutes. The results were that different people had different results, but on average, tic frequency and severity decreased (by about 30%; see Figure 5 in the reference below). A few participants reported dramatic benefit during stimulation (see video S1). Their experience, of course, has generated substantial interest from the public.

This experiment is very clever, and provides a possible new treatment. However, important questions remain. Can the improvement be made to last more than a few minutes? How many people improve with MNS? Can we predict who will benefit and who won’t? Does the stimulation have to be rhythmic to produce clinical benefit? Can the stimulation be provided, say, for 5 seconds every minute, or does it need to be continuous? We need to know some of these answers before we know how useful MNS may be in real life.

I have talked with the researchers from Nottingham, who are continuing with this line of research, and we plan to enroll some patients here. However, our research has been on hold since the start of the COVID-19 restrictions, we need to get ethics approvals, and we want to plan carefully so that we do the research right.

As soon as we are ready to enroll volunteers, we will post an addendum here with further information on testing MNS here at Washington University. In the meantime, it’s worth remembering that several effective treatments for tics are already available, and we are also testing new medications and behavior therapies.

Reference

Morera Maiquez B et al.: Entraining Movement-Related Brain Oscillations to Suppress Tics in Tourette Syndrome. Current Biology 2020; DOI 10.1016/j.cub.2020.04.044.

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