Ballismus

Ballismus is a hyperkinetic movement disorder characterized by involuntary, violent, flinging motions of one or both limbs. The movements are typically large‑amplitude, sudden, and irregular, distinguishing ballismus from the smaller, repetitive movements of chorea. When the abnormal movements affect only one side of the body, the condition is called hemiballismus; involvement of both sides is referred to as bilateral ballismus.

The most common cause of hemiballismus is a lesion in the subthalamic nucleus, frequently due to a lacunar infarct in the territory of the lenticulostriate arteries. Other etiologies include intracerebral hemorrhage, traumatic brain injury, tumors, infections, metabolic disturbances, and neurodegenerative diseases such as Huntington’s disease. Drug‑induced ballismus can occur with dopamine‑enhancing agents, antipsychotics withdrawn abruptly, or certain stimulants.

Clinically, patients present with rapid, proximal jerks that can bring the limb to a flail or ballistic trajectory, often worsening at rest and diminishing during purposeful activity. The movements may be triggered by sudden stimuli and can impair activities of daily living or cause injury. Diagnosis relies on a thorough neurological examination and neuroimaging, typically magnetic resonance imaging, to identify structural lesions. Laboratory testing may be employed to exclude metabolic or infectious contributors.

Management focuses on treating the underlying cause and reducing the hyperkinetic movements. Pharmacologic options include dopamine‑depleting agents such as tetrabenazine, GABA‑ergic drugs like clonazepam or baclofen, and, in refractory cases, neuroleptics or deep brain stimulation targeting the subthalamic nucleus. Prognosis varies: lesions that resolve or are surgically addressed often lead to marked improvement, whereas persistent structural damage may result in chronic motor dysfunction.