Single photon emission tomography (SPET) imaging of dopamine D2 receptors in the course of dopamine replacement therapy in patients with nocturnal myoclonus syndrome (NMS)

Abstract

Single photon emission tomography (SPET) permits the in vivo measurements of regional cerebral radioactivity in the human brain following the administration of compounds labeled with photon-emitting isotopes. According to our SPET findings of a reduced binding of [¹²³I]labeled (S)-2-hydroxy-3-iodo-6-methoxy-([1-ethyl-2-pyrrolidinyl]methyl) benzamide (IBZM) (a highly selective CNS D₂ dopamine receptor ligand) to D₂ dopamine receptors in striatal structures in untreated patients with nocturnal myoclonus syndrome (NMS) it seemed to be of interest to investigate whether there are changes in D₂ receptor binding under dopamine replacement therapy or not. We studied the uptake and distribution of [¹²³I]IBZM before and in the course of dopamine replacement therapy in four patients with severe insomnia caused by a nocturnal myoclonus syndrome (NMS). We found an increase of the IBZM binding to D₂ receptors in the course of treatment, which was associated with an improvement of sleep quality. Reasons for this are discussed. The [¹²³I]IBZM SPET technique in conclusion offers an interesting tool for in vivo investigations of functional changes in the dopaminergic neurotransmitter system in longitudinal studies.