[A case of thalamo-subthalamic hemorrhage presenting monoballism in the contralateral lower extremity].

We report a 62-year-old man with ballism confined to the right leg, so-called monoballism. He was admitted to our hospital complaining of gait disturbance due to violent involuntary movements in the right lower extremity which had developed seven days before. He had a ten-years' history of hypertension and at age 57 had been diagnosed as having asymptomatic multiple cerebral infarcts. Until admission, he was taking antiplatelet drugs for the purpose of preventing thrombotic stroke. On neurological examination, he showed mild impairment of higher brain function, Horner's sign in the left eye, and typical ballism in the right lower extremity. Involuntary movements were never observed in the face and the other extremities. Surface electromyography also showed reciprocal burst discharges at about 1 Hz related to the ballistic movements in the right lower extremity. CT scan revealed a high density lesion surrounded by a low density in the left subthalamic area. MRI examination demonstrated a dumbbell shaped hemorrhage extending from the left subthalamic nucleus to the dorsomedial nucleus of the ipsilateral thalamus. Adding to the hemorrhage, many ischemic lesions were observed in the bilateral basal ganglia and thalamus including the left pallidum. The causal end of the hemorrhage apparently located in the anterior dorsomedial portion of the subthalamic nucleus. There were few reports concerning monoballism, especially monoballism limited to the lower extremity. Recent researches indicate that a subthalamic lesion reduces the excitatory control from the subthalamus to the internal segment of the globus pallidus, which leads to a disinhibition of the thalamus and gives rise to ballism.(ABSTRACT TRUNCATED AT 250 WORDS)