FP-CIT- and IBZM-SPECT in Corticobasal Syndrome: Results from a Clinical Follow-Up Study

Objective: To evaluate the striatal presynaptic dopamine transporter (FP-CIT-SPECT) and postsynaptic D2 receptor (IBZM-SPECT) binding in patients with corticobasal syndrome (CBS). Background: FP-CIT and IBZM are commercially available and approved SPECT tracers for in vivo molecular imaging of pre- and postsynaptic nigrostriatal neuronal degeneration, but only few data for CBS are available. Methods: 23 patients meeting clinical criteria for early- to mid-stage CBS (disease duration ≤4 years) were examined with SPECT radiotracers FP-CIT and IBZM. All suspected CBS patients underwent a clinical follow-up examination and were re-evaluated after 19.7 ± 15.2 months (mean ± SD). Postmortem diagnosis was available for 2 patients. In patients who met research criteria for probable CBS at the final follow-up visit (n = 19; disease duration: 1.95 ± 0.91 years), SPECT binding values were compared to those of age- and gender-matched Parkinson's disease (PD) patients (n = 18, disease duration: 1.92 ± 0.91 years; clinical follow-up: 32 ± 29.6 months) and neurologically normal control subjects (n = 19). Results: In comparison to the healthy control subjects, both patient groups showed significant and asymmetric reduction of the striatal presynaptic dopamine transporter binding, but PD patients had significantly lower FP-CIT binding ratios than probable-CBS patients. FP-CIT binding values of probable-CBS patients and healthy controls demonstrated marked overlaps, and in 7 patients (39%) scans revealed no dopaminergic deficit. IBZM uptake did not show significant between-group differences. Conclusion: Our data indicate that in the early- to mid-stage CBS the degree of nigrostriatal impairment is only mild with a significant proportion of preserved dopamine transporter binding.