Myoclonus and the Cavalier King Charles Spaniel Myoclonus is a type of uncontrollable movement that includes sudden, brief involuntary twitching, jerking, or spasm of a single muscle or a group of muscles. A dog or cat experiencing myoclonus cannot control it. Myoclonus is the word for the movements themselves. It is not a disease itself, but may be a sign of another neurological condition. Myoclonus associated with epileptic seizures has been described in dogs and cats while non-epileptic forms