THALAMOTOMY FOR POSTAPOPLECTIC HEMIBALLISTIC CHOREA IN OLDER ADULTS

To the Editor: Excessive, spontaneous movements that are irregularly timed, nonrepetitive, randomly distributed, and abrupt in character characterize chorea, an involuntary movement disorder.1 Causes of chorea include levodopa treatment for Parkinson's disease; Huntington's disease; and more rarely, infection, metabolic disorders, and cerebrovascular insults.1, 2 Some cases of chorea can be successfully treated medically using neuroleptics such as tetrabenazine,2 but previously fit and healthy older adults presenting with an acute disabling movement disorder, refractory to medical treatment, pose a special therapeutic challenge. Thalamotomies and pallidotomies are targeted brain lesional procedures that can be performed using heat, cold, or chemical means, the most common procedure currently being stereotactic radiofrequency thermocoagulation. Such ablative procedures were first introduced for chorea more than half a century ago3 but because of only modest improvements were largely abandoned soon after. They have recently been revisited because of an increasing demand for therapeutic options for debilitating movement disorders, not least in a growing older population and in third world countries.4, 5 An 88-year-old right-handed woman presented with acute onset of large-amplitude unilateral right-leg chorea. Her symptoms were unremitting, persisting during daytime and noted during sleep. She could move her leg voluntarily. She received treatment with tetrabenazine 25 mg daily with little effect. She had mild hypertension. Medications included aspirin, dipyridamole, and a statin daily. On examination, she had no neurological abnormalities other than the large-amplitude choreiform movements of the right leg. Brain magnetic resonance imaging (MRI) showed high signal changes in the periventricular white matter consistent with small-vessel ischemic disease. The acute hemiballistic chorea was thought to be the result of a new ischemic lesion of the contralateral (left) subthalamic nucleus. Two months after onset of the chorea, a left-sided stereotactic neurosurgical procedure was scheduled under local anesthesia, enabling the patient to self-report her symptoms and remain neurologically assessable. Aspirin and dipyridamole were stopped 1 week before surgery. A Brown-Roberts-Wells stereotactic head frame was positioned, and a computed tomography scan of the head was performed and fused with the MRI scan. The left ventrooralis posterior (VOP) nucleus of the thalamus was targeted using a stereotactic planning software workstation (StereoPlan, Radionics, Burlington, MA), targeting the anatomical coordinates at a predefined distance from the anterior commissure–posterior commissure line and verified on the Schaltenbrand anatomical atlas.6 Perioperative test stimulation in the VOP nucleus of the thalamus was performed at 100 Hz, 500 μs, and 2 V, producing mild contralateral leg sensory symptoms. A permanent left-sided thalamic VOP lesion was performed using radiofrequency thermocoagulation (Cosman, Boston, MA) in three steps by heating the electrode tip to 80°C for 70 seconds each time (Figure 1). The choreiform movements of the right leg were markedly reduced immediately postoperatively, although she developed mild right-sided limb weakness and mild dysarthria in the immediate postoperative days that gradually resolved over 6 weeks. Postoperative T1 axial magnetic resonance imaging brain image showing the left-sided thalamotomy lesion (arrow). On follow-up 6 weeks postoperatively, she continued to have excellent relief of the right-sided leg chorea. Her right-sided weakness and dysarthria had largely resolved. She was walking with a frame, displaying occasional mild choreiform movements of the right foot. On last follow-up, 6 months after the procedure, the effect was not fully maintained, although she continued to be significantly better than preoperatively. Although deep brain stimulation has provided benefits in certain types of chorea in recent years,7, 8 ablative surgery has also been used successfully for levodopa-induced dyskinesia, both choreic and ballistic, in Parkinson's disease.9 Also, in a patient with hemichorea after a subthalamic hemorrhage, ventralis oralis complex thalamotomy abolished choreiform movements over a sustained period of time.10 Chorea and ballism are thought to be the result of a loss of subthalamic excitatory output to the basal ganglia output nuclei (the globus pallidus internus and substantia nigra pars reticulata), resulting in unrestrained activity of the thalamocortical projections with resulting choreic or ballistic movements.11 Thus it appears that the choreiform symptoms can be successfully relieved through interference with these mechanisms using thalamic ablative or deep brain stimulation therapy. Deep brain stimulation is considered to be safer than lesional surgery, particularly for bilateral procedures, with lower risk of hemorrhage and speech disturbances,4 although there remain situations in which ablational surgery may provide a feasible alternative.5 Advantages of lesional therapy over deep brain stimulation include less need for access to specialists and clinical follow-up, no risk of hardware failure requiring reoperation, greater affordability, and lower risk of infection.4, 5 Ablative surgery may therefore be particularly useful in the setting of a previously healthy and independent older person with limited life expectancy who presents with a sudden-onset disabling movement disorder refractory to medical therapy. Conflict of Interest: The authors declare no conflict of interest. Author Contributions: AA, PS, CJ, BF, WT, and TA recruited subject and performed the case study. AA, EP, AG, and TA wrote the letter. Sponsor's Role: None.