What type of movement disorder is characterized by a combination of stiffness and involuntary movements?

The type of movement disorder characterized by a combination of stiffness and involuntary movements is dystonia. Dystonia involves sustained muscle contractions, which may lead to twisting or repetitive movements, as well as abnormal posture. The stiffness associated with dystonia arises from the increased muscle tone that characterizes the condition. Importantly, these involuntary movements can occur in various parts of the body, and they may fluctuate or change in response to different activities or external stimuli.

In contrast, spasticity primarily refers to an increase in muscle tone and resistance to passive movement due to hyperexcitability of the stretch reflex, which does not typically include the same kinds of involuntary movements seen in dystonia. Athetosis is characterized mainly by slow, writhing movements that primarily affect the hands and feet but does not inherently involve the stiffness that defines dystonia. Cerebellar ataxia, on the other hand, manifests as a lack of coordination and balance, often accompanied by tremors, but does not include the stiffness or sustained contractions that are hallmark features of dystonia. Therefore, dystonia is the most accurate classification for a movement disorder that displays both stiffness and involuntary movements.