I-123 BETA-CIT AND I-123 IBZM-SPECT SCANNING IN LEVODOPA-NAIVE PARKINSONS-DISEASE

Striatal dopamine transporter function and dopamine D2 receptor status were evaluated in 15 patients with early untreated Parkinson's diseas e using single photon emission tomography (SPECT) with I-123-Iodo-2 be ta-carboxymethoxy-3 beta-(4-idiophenyl)tropane (beta-CIT) and I-123- I odobenzamide (IBZM) as pre- and postsynaptic ligands. Symptoms were un ilateral in five patients and bilateral but asymmetric in 10 patients. Patients with bilateral symptoms had significantly lower 18-hour stri atal/cerebellar beta-CIT binding ratios (3.59 +/- 0.79) than hemiparki nsonian patients (5.76 +/- 1.48, p < 0.05) reflecting more advanced di sease in this sub-group. Patients with bilateral parkinsonism were als o found to have a significant side-to-side difference in striatal beta -CIT binding with more marked reduction contralateral to the presentin g limb (18-hour striaral/cerebellar ratio: 4.13 +/- 0.78 [ipsilateral] versus 3.59 +/- 0.79 [contralateral], p < 0.05). Dopamine D2 receptor binding as measured by IBZM was significantly elevated contralateral to the affected side in hemiparkinsonian patients (striatal/cerebellar ratio: 2.42 +/- 0.90 [contralateral] versus 2.19 +/- 0.80 [ipsilatera l], p < 0.05). This asymmetric upregulation was absent in the patients with bilateral parkinsonism (striatal/cerebellar ratio: 1.85 +/- 0.43 [contralateral to more severely affected side] versus 1.83 +/- 0.34 [ ipsilateral], p > 0.05), Our data suggest that postsynaptic dopamine r eceptor upregulation contralateral to the presenting side occurs in un heated unilateral PD and disappears in untreated bilateral (asymmetric ) PD despite a greater loss of dopamine transporter function. Combined beta-CIT and IBZM SPECT studies may be helpful to monitor the progres sion of nigrostriatal dysfunction in early PD.