Correlation of clinical response in apomorphine test with D2-receptor status as demonstrated by 123I IBZM-SPECT.

The knowledge of functional capacities of postsynaptic dopaminergic receptors in parkinsonian syndromes is important for differential diagnosis and for planning therapeutic approaches. Subcutaneous apomorphine challenges serve as a pharmacological tool in testing dopaminergic responsiveness, but discrepancies between results of the apomorphine test and long-term levodopa treatment remain. 123I IBZM (I-123 labeled iodobenzamide) as a dopaminergic receptor ligand allows depiction of D2-receptors by means of SPECT methods. The correlation between dopaminergic responsiveness and D2-receptor status as demonstrated by 123I IBZM-SPECT imaging was assessed by applying an apomorphine test to 41 patients with parkinsonian syndromes. All subsequently underwent an 123I IBZM-SPECT. Apomorphine responders showed a significantly higher binding of 123I IBZM than nonresponders, and patients with idiopathic Parkinson's disease (IPD) had higher D2-receptor density as visualized by SPECT than patients with other parkinsonian syndromes. The marked overlap between the groups allowed a reliable prediction only in patients with an abnormally low basal ganglia/frontal cortex ratio of 123I IBZM binding.