Dystonia is another type of hypertonia (high tone) that may be found in spastic diplegia. In contrast to spasticity, dystonia does not occur as a result of rapid stretch. In a person with dystonia, sustained muscle contractions cause twisting and repetitive movements or abnormal postures. Examples of dystonia are where the leg muscles may tighten when talking or playing a video game (where there is excitement or tension), or uncontrolled, writhing/posturing movements of the fingers or toes.
Collison L (2020) Spastic Diplegia–Bilateral Cerebral Palsy. St Paul: Gillette Children’s Specialty Press.