Iodine-123-IBZM dopamine D2 receptor and technetium-99m-HMPAO brain perfusion SPECT in the evaluation of patients with and subjects at risk for Huntington's disease.

Huntington's disease (HD) is pathologically characterized by neuronal loss and neuroreceptor alterations in the striatum, including a reduction in dopamine receptor density. We evaluated the clinical usefulness of 123I-iodobenzamide (IBZM) D2 receptor SPECT imaging and 99mTc-hexamethylpropyleneamineoxime (HMPAO) brain perfusion SPECT imaging by studying four early symptomatic HD patients, 20 asymptomatic subjects at risk for HD and 22 controls. Striatal D2 receptor binding and perfusion were measured semiquantitatively by calculating striatum-to-frontal cortex IBZM and HMPAO uptake ratios, respectively. The control IBZM ratio (1.58 +/- 0.06) declined with age at 1.5% per decade (r = -0.58, p < 0.005), whereas the HMPAO ratio (1.15 +/- 0.05) did not. All four symptomatic patients had decreased IBZM ratios and three patients also had decreased HMPAO ratios. Five of 20 at-risk subjects had decreased IBZM ratios and two subjects also had decreased HMPAO ratios. Three of the five at-risk subjects showed subtle nonchoreic neurological abnormalities. Decreased striatal D2 receptor binding thus may be detected by IBZM-SPECT in the asymptomatic as well as symptomatic groups, and these changes were more marked than perfusion deficits detected by HMPAO-SPECT. IBZM-SPECT thus appears to be a promising method for early diagnosis and preclinical detection of HD.