A patient with contralateral hemiballismus is most likely to have a lesion in which area of the brain?

• A. Caudate nucleus
• B. Globus pallidus
• C. Putamen
• D. Subthalamus

Answer: (D)

Contralateral hemiballismus is primarily associated with a lesion in the subthalamus. This movement disorder results from a disruption in the basal ganglia circuitry, particularly affecting the balance of excitatory and inhibitory signals that regulate voluntary movements. The subthalamic nucleus plays a crucial role in modulating motor control by providing excitatory input to the globus pallidus internus and substantia nigra pars reticulata.

When there is a lesion in the subthalamus, there is a loss of the regulatory influence it exerts over the downstream structures. This leads to increased activity within the thalamus and motor cortex, resulting in the involuntary, rapid, and irregular movements characteristic of hemiballismus affecting the opposite side of the body, which is referred to as contralateral hemiballismus.

This understanding highlights the specific anatomical and functional relevance of the subthalamic nucleus in the pathology of this movement disorder, making it the most likely location of a lesion in cases presenting with contralateral hemiballismus.