Acta Neurochir (Wien) (2008) 150: 395–397 DOI 10.1007/s00701-008-1549-2 Printed in The Netherlands Case Report Subthalamic nucleus metastasis causing hemichorea-hemiballism treated by gamma knife stereotactic radiosurgery I. Karampelas 1 , M. B. Podgorsak 2 , R. J. Plunkett 1 , R. A. Fenstermaker 1 1 Department of Neurosurgery, School of Medicine and Biomedical Sciences, Roswell Park Cancer Institute, State University of New York, NY, USA 2 Department of Radiation Medicine and Physics, School of Medicine and Biomedical Sciences, Roswell Park Cancer Institute, State University of New York, NY, USA Received 28 March 2007; Accepted 18 January 2008; Published online 3 March 2008 # Springer-Verlag 2008 Introduction The subthalamic nucleus (STN) is an important re- lay that modulates the activity of the basal ganglia [1]. Hemichorea-hemiballism (HC-HB), characterized by in- voluntary unilateral flinging movements of the limbs, has been linked to lesions of the STN. Reported cases of metastatic tumours of the STN are distinctly rare [2]. We present the case of a woman who became symptom- atic from a metastatic brain tumour involving the STN and was treated with gamma knife stereotactic radiosur- gery (GKSR). To our knowledge, this is the first report of GKSR used as treatment for metastatic tumour caus- ing HC-HB. Case presentation A 62 year-old woman with carcinoma of the breast presented with 6 weeks of difficulty controlling her right upper extremity due to abrupt involuntary, mostly proximal, flailing movements. Examination showed spontaneous, choreiform movements of the right arm and hand with associated pseudo-purposeful gestures. MRI revealed a 10 mm lesion in the left subthalamus (Fig. 1A and B). We treated the patient’s tumour with a Leksell gam- ma knife. The treatment plan consisted of 9 isocenters delivered using a 4 mm collimator helmet. The pre- scription dose was 18 Gy administered to the 50% iso- dose surface at the tumour margin. Tumour coverage was 99% with a dose-volume histogram ratio of 1.25 (Fig. 1C and D). The patient was placed on topiramate 50 mg twice daily with some improvement in her HC-HB, as docu- mented by serial video recording. A post-radiosurgical MRI scan at 1 month revealed a decrease in the maxi- mal diameter of the tumour to 8 mm. The patient’s clinical neurological status remained stable. Three months after treatment, she died of systemic complica- tions of her cancer. Discussion A range of disease processes can cause HC-HB, with stroke being the most common. The differential diagnosis includes primary and metastatic neoplasms, haemorrhage, vascular malformations, tuberculomas, demyelinating plaques, tuberous sclerosis and toxo- plasmosis [3]. Other medical conditions can cause HC-HB, such as non-ketotic hyperglycemia, hypocal- caemia, lupus vasculitis, leukaemic infiltration of the Correspondence: Ioannis Karampelas, MD, Department of Neuro- logical Surgery, Weill Medical College of Cornell University, 525 E 68 th Street, Box 99, NY 10021, USA. e-mail: ikarampelas@yahoo.com