THE METABOLIC TOPOGRAPHY OF IDIOPATHIC TORSION DYSTONIA

We used [F-18]fluorodeoxyglucose (FDG) and PET with a statistical mode l of regional metabolic covariation to study brain topographic organiz ation in idiopathic torsion dystonia (ITD). We studied 11 patients wit h predominantly right-sided ITD and 11 age-matched controls, and measu red global, regional cerebral and normalized metabolic rates for gluco se (GMR, rCMRGlc, uCMRGlc/GMR). The Scaled Subprofile Model was applie d to the combined rCMRGlc dataset to identify topographic covariance p rofiles associated with ITD. We found that global and regional metabol ic rates were normal in ITD. The SSM analysis of the combined groups o f ITD patients and normals revealed a significant topographic profile characterized by relative bilateral increases in the metabolic activit y of the lateral frontal and paracentral cortices, associated with rel ative covariate hypermetabolism of the contralateral lentiform nucleus , pens and midbrain. Subject scores for this profile correlated signif icantly with Fahn-Marsden disease severity ratings (r = 0.67, P < 0.02 ). In contrast to parkinsonism, lentiform and thalamic metabolism were dissociated in dystonia. We conclude that ITD is characterized by rel ative metabolic overactivity of the lentiform nucleus and premotor cor tices. The presence of lentiform thalamic metabolic dissociation sugge sts that in this disorder hyperkinetic movements may arise through exc essive activity of the direct putameno-pallidal inhibitory pathway.