THE METABOLIC ANATOMY OF TREMOR IN PARKINSONS-DISEASE

Objective: To identify regional metabolic brain networks related speci fically to the presence of tremor in PD, Background: The pathophysiolo gy of parkinsonian tremor is unknown. Because tremor in PD occurs main ly in repose, we used resting state PET with F-18-fluorodeoxyglucose ( FDG) to identify specific metabolic brain networks associated with thi s clinical manifestation. Methods: We studied two discrete groups of e ight PD patients with and without tremor using FDG/PET. Both patient g roups were matched for gender, age, and Unified Parkinson Disease Rati ng Scale ratings for akinesia and rigidity. Ten normal volunteer subje cts served as controls. Results: Network analysis with the Scaled Subp rofile Model was performed in two steps. 1) We computed the expression of the PD-related pattern (PDRP) identified by us previously in each of the PD patients and control subjects. Although PDRP subject scores were abnormally elevated in the combined PD cohort (p < 0.005), these values did not differ in the PD patient groups with and without tremor (p = 0.36), 2) We used SSM to analyze the data from the combined PD c ohort comprising both patient groups. We found that PD patients with t remor were characterized by increased expression of a metabolic networ k comprising the thalamus, pens, and premotor cortical regions. Subjec t scores for this pattern were elevated in the tremor group compared w ith the atremulous patient group and the normal control group (p < 0.0 05), Conclusions: The findings suggest that PD patients with tremor ar e characterized by distinct increases in the functional activity of th alamo-motor cortical projections. Modulation of this functional anatom ic pathway is likely to be the mechanism for successful interventions for the relief of parkinsonian tremor.