Cats may experience involuntary muscle trembling, twitching, or spasms which can occur for various reasons. Muscle trembling may be caused by a genetic condition and is untreatable but is not harmful. Uncontrollable muscle twitching can also be an emotional response or a reaction to irritants and isn't necessarily related to any medical condition. However, some health issues that cause muscle trembling can be severe and possibly life-threatening. If the muscle trembling persists, book an appointment with your vet immediately.