I dont know but its a common symptom, ive had extreme twitching all over my body since i was 18, pre dating the ME /CFS because a lot of people can get this, and if tests do not indicate disease, then the condition is ignored, i know because this twitching condition has been ignored all my life. But there seems to be a lot of ME/CFS patients who have this for sure. Thats all i know. sorry if it doesnt help