TRODAT-1 and Tc-99m ECD observations in hyperglycemia hemichorea

We describe two cases of right hyperglycemia hemichorea (HGHC) with identical Tc-99m TRODAT-1/ Tc-99m ECD scan findings. While the brain MRI showed signal alterations within the left putamen, there was evidence of hyperperfusion on Tc-99m TRODAT-1 but hypoperfusion on Tc-99m ECD within the left putamen, in association with hyperperfusion within left thalamus on Tc-99m ECD. The discrepancy between the Tc-99m TRODAT-1 and Tc-99m ECD scan provides insight into the imbalance between direct and indirect circuits along the nigrostriatal pathway, as the fundamental genesis of HGHC. Furthermore, the hyperperfusion at the left thalamus represents thalamic disinhibition secondary to loss of pallidal negative control, which ultimately leads to HGHC through re-entrant outflow to the motor cortex. Neurology Asia 2016; 21(1) : 85 – 87 Address correspondence to: Dr. Min-Chien Tu, Department of Neurology, Buddhist Tzu Chi General Hospital Taichung Branch, No.66, Sec. 1, Fengxing Rd., Tanzi Dist., Taichung City 427, Taiwan (R.O.C.) Tel: +886-4-3606-0666 ext 4913, E-mail: [email protected] INTRODUCTION Hyperglycemia hemichorea (HGHC) is a rare syndrome characterized by unilateral chorea in the context of a hyperglycemic state and characteristic neuroradiological findings within the contralateral striatum. Patchy hyperintensities within the putamen and/or caudate nucleus in T1 weighted imaging of magnetic resonance imaging (MRI) are regarded as the main radiological features. Although HGHC has been recognized as a unique clinical-radiological syndrome for years, its mechanisms have remained obscure. While histological studies using biopsy specimens have described gemistocytic astrocytosis, autopsy cases of more complicated clinical profiles have shown infarct, reactive astrocytosis, or inconsistent mineral deposits. Studies dedicated to structural neuroimaging once proposed microhaemorrhage, mineral deposition, ischemic insults, and altered hemodyamics from a venous anomaly as the favored causes of HGHC. However, there have been few functional imaging reports in the literature. We herein elaborate two cases of HGHC and probe its underlying pathogenesis by incorporating MRI findings with observations from a Technetium-99m TRODAT-1 scan (Tc-99m TRODAT-1) and Technetium-99m ethyl cysteinate dimmer (Tc-99m ECD). CASE REPORTS