CLINICAL CASE | Involuntary Unilateral Ballistic Limb Movements
A 65-year-old man with a history of hypertension suddenly developed involuntary, violent, ballistic movements of his right arm and leg. The movements primarily involved flexion and rotation of the proximal parts of the limbs. MRI showed a small hemorrhagic lesion in the left diencephalon (Figure 14–1A). Despite the diencephalic location of the lesion, the neurologist called to examine the patient suspects basal ganglia involvement.
Answer the following questions based on your reading of this chapter and relevant sections from other chapters.
1. Are the motor signs consistent with damage to the pyramidal system or cerebellum?
2. How is the diencephalon linked with basal ganglia motor functions and how might that lead to a motor impairment?
3. Explain why the aberrant ballistic movements are on the contralateral side.
4. Occlusion of which cerebral artery and branch could produce a lesion such as the one shown in Figure 14–1? Key neurological signs and corresponding damaged brain structures Subthalamic nucleus circuitry
The subthalamic nucleus is a diencephalic structure that is part of the indirect pathway of the basal ganglia. It receives GABAergic inputs from the external segment of the globus pallidus and projects to the internal segment of the globus pallidus. From there, information is directed to the motor thalamus, and then the motor cortex, which controls movements contralaterally, via the corticospinal tract. Additionally, the subthalamic nucleus receives dense glutamatergic inputs from the motor cortex, primarily on the ipsilateral side. Whereas the cortical-basal ganglia circuitry is ipsilateral, it exerts its movement control influence on the contralateral side because the corticospinal tract is predominantly crossed. The nucleus is somatotopically organized; the lesion shown in Figure 14–1A is sufficiently large to affect both its arm and leg areas of this small nucleus.
Because the subthalamic nucleus normally activates an inhibitory structure—the internal segment of the globus pallidus—when it is lesioned it is reasoned that this inhibition is less. Hemiballism, the condition resulting from subthalamic nucleus lesion, is thus thought to be produced by disinhibition; it is a release phenomenon. It is not known why this is reflected in the violent proximal movements, so much a signature of subthalamic nucleus damage.
The largest portion of the subthalamic nucleus is devoted to limb and trunk motor functions. In addition, smaller regions of the nucleus are more important for eye movement control, emotional, and cognitive functions. These regions are parts of the ocular motor, limbic, and cognitive loops of the basal ganglia. References
Brust JCM. The Practice of Neural Science. New York, NY: McGraw-Hill; 2000.
Hamani C, Saint-Cry JA, Fraser J, Kaplitt M, Lozano A. The subthalamic nucleus in the context of movement disorders. Brain. 2004;127:4-20.
Kitajima M, Korogi Y, Kakeda S, et al. Human subthalamic nucleus: evaluation with high-resolution MR imaging at 3.0 T. Neuroradiology. 2008;50(8):675-681.
Nishioka H, Taguchi T, Nanri K, Ikeda Y. Transient hemiballism caused by a small lesion of the subthalamic ...