SPECT study of the nigrostriatal dopaminergic system in Huntington's disease

The pathological process of Huntington's disease (HD) preferentially targets spiny neurons in the striatum, with later involvement of the substantia nigra and other structures. The purpose of this study is to investigate the nigrostriatal dopaminergic system in a genetically confirmed HD family.

We used single photon emission computed tomography (SPECT) with the radiotracers [(99m) Tc]TRODAT-1 and [123I]IBZM to study the binding potentials of dopamine transporter (DAT) and dopamine D2 receptors in the striatum of 3 symptomatic HD patients, 1 mutation-negative member of the HD family, and 7 healthy controls. Specific binding potentials were calculated as (striatum-occipital lobe)/occipital lobe.

Reduced binding potential of striatal dopamine D2 receptors was found in the 3 symptomatic HD patients. The DAT binding potential was reduced in 1 symptomatic HD patient. We also found that the more severe the clinical status, the lower the DAT and D2 receptor binding potentials, and the larger the bicaudate ratio.

We showed that the postsynaptic part of the nigrostriatal pathway was involved. The presynaptic part is usually not affected but could occur in very advanced cases. Our findings suggest that SPECT imaging of D2 receptors is useful for diagnosing and monitoring HD.