Which movement disorder is characterized by gross, abrupt contractions?

• A. Myoclonus
• B. Ballismus
• C. Chorea
• D. Dystonia

Answer: (B)

The movement disorder characterized by gross, abrupt contractions is ballismus. This condition involves large, flinging movements of the limbs, often resulting from damage to the basal ganglia, particularly the subthalamic nucleus. These movements are typically seen as sudden, erratic, and can be quite forceful, making them distinct from other movement disorders.

In contrast, myoclonus involves brief, shock-like jerks of a muscle or group of muscles, which are typically smaller and more localized than the movements seen in ballismus. Chorea consists of irregular, non-repetitive, and dance-like movements that can be of varied amplitude, but they lack the gross and abrupt nature associated with ballismus. Dystonia is characterized by sustained muscle contractions leading to twisting and repetitive movements, which again differs from the quick, large-scale motions seen in ballismus. Hence, the defining characteristic of ballismus is its gross and abrupt contractions, making it the correct choice for this question.