A man I used to work with had this ailment, I think. I didn't know the name of it, but the symptoms are similar. He was upbeat and friendly. He walked with a cane, but every so often as he was walking, his ankle and foot would come off the floor and shake uncontrollably.
He told me once that he was in a car accident and injured his spine, and that's how his problem started. He said that there was nothing they could do for him. He was stuck with this condition and so he has just accepted it.