THE METABOLIC TOPOGRAPHY OF PARKINSONISM

We used [F-18]fluorodeoxyglucose/positron emission tomography (F-18-FD G/PET) and a statistical model of regional covariation to study brain topographic organization in parkinsonism. We studied 22 patients with Parkinson's disease (PD), 20 age-matched normal volunteers, and 10 age - and severity-matched patients with presumed striatonigral degenerati on (SND). We used FDG/PET to calculate global, regional, and normalize d metabolic rates for glucose (GMR, rCMR(glc), rCMR(glc)/GMR). Metabol ic parameters in the three groups were compared using an analysis of v ariance, with a correction for multiple comparisons, and discriminant analysis. The scaled subprofile model (SSM) was applied to the combine d rCMR(glc) dataset to identify topographic covariance profiles that d istinguish PD patients from SND patients and normals. GMR, rCMR(glc), and rCMR(glc)/GMR were normal in PD; caudate and lentiform rCMR(glc)/G MR was reduced in the SND group (p < 0.01). SSM analysis of the combin ed group of patients and normals revealed a significant topographic pr ofile characterized by increased metabolic activity in the lentiform n ucleus and thalamus associated with decreased activity in the lateral frontal, paracentral, inferior parietal, and parietooccipital areas. I ndividual subject scores for this profile were significantly elevated in PD patients compared with normals and SND patients (p < 0.001) and discriminated the three groups. In the PD group, subject scores for th is factor correlated with individual subject Hoehn and Yahr (H&Y) scor es (p < 0.02), and with quantitative rigidity (p < 0.01) and bradykine sia (p < 0.03) ratings, but not with tremor ratings. SSM analysis of r ight-left metabolic asymmetries yielded a topographic contrast profile that accurately discriminated mildly affected PD patients (H&Y Stage I) from normals. Our findings demonstrate that abnormal topographic co variance profiles exist in parkinsonism. These profiles have potential clinical application as neuroimaging markers in parkinsonism.