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Regional Analysis of D2 Dopamine Receptors in Parkinson's Disease Using SPECT and Iodine-123-Iodobenzamide

Geriatric Research, Education and Clinical Center, Department of Veterans Affairs Medical Center
Departments of Neurology and Radiology, University of Florida College of Medicine, Gainesville, FL
Department of Psychiatry, Medical University of South Carolina, Charleston, South Carolina

Correspondence: For correspondence or reprints contact: Stephen E. Nadeau, MD, GRECC(182), VAMC, Gainesville, FL 32608-1197.

ABSTRACT

The goal of this study was to examine the relationship between D2 dopamine receptor density and levodopa dosage, disease duration and dyskinesia in Parkinson's disease (PD). Methods: Iodine-123-iodobenzamide SPECT scans were obtained from 14 PD patients and 12 age-matched controls using a three-headed camera in conjunction with MRI and a fiducial-based image registration system to define regions of interest. Basal ganglia/cerebellum counts/voxel ratios in dorsal and ventral head of caudate and anterior and posterior putamen were measured at 30, 60, 120 and 180 min postinjection. As in ¹¹C-raclopride studies, ratios obtained at that time when they asymptomatically approach a maximum value (180 min) were accepted as the best measure of receptor density. Results: Among PD patients, a trend towards an inverse correlation between regional basal ganglia/cerebellum ratios and levodopa dosage achieved significance in ventral caudate (F = 6.244, p = 0.037); similarly, an inverse correlation between these ratios and disease duration achieved significance in anterior putamen (F = 13.144, p = 0.007). Ratios were significantly lower in anterior putamen in patients with dyskinesia (t = 3.068, p = 0.042). Conclusion: in PD, the previously observed inverse correlation between levodopa dosage and D2-receptor density appears to be most prominent in the least dopamine-deplated region, ventral caudate. There may be a genuine effect of disease duration on receptor density in putamen and reduced receptor density in anterior putamen may be associated with dyskinesia.

Key Words: dopamine receptors • D2 receptors • iodobenzamide • SPECT • Parkinson's disease