Striatal Dopamine Transporter Binding Assessed by [I-123]IPT and Single Photon Emission Computed Tomography in Patients With Early Parkinson's Disease

Background

Specific binding to dopamine transporters may serve as a tool to detect early loss of nigrostriatal dopaminergic neurons in patients with Parkinson's disease.

Objective

To determine striatal dopamine transporter binding using the cocaine analogue [I-123]N-(3-iodopropen-2-yl)-2β-carbomethoxy-3β-(4-chlorophenyl) tropane ([I-123]IPT) and single photon emission computed tomography.

Patients and Methods

We studied 9 control subjects (mean age, 58 years; range, 41-69 years) and 28 patients with early Parkinson's disease (Hoehn and Yahr stages I [n = 14] and II [n = 14] [symptom duration, <5 years]; mean age, 55.5 years; range, 36-71 years). Single photon emission computed tomography was performed 90 minutes after injection of 120 to 150 MBq of radioactive [I-123]IPT.

Results

Specific striatal [I-123]IPT binding (mean ± SD) was significantly reduced in patients with early Parkinson's disease (ipsilateral striatum: 4.09 ± 0.97; range, 2.46-6.40; contralateral striatum: 3.32 ± 0.76; range, 1.80-5.13) compared with controls (left striatum: 7.28 ± 0.94; range, 5.78-8.81; right striatum: 7.41 ± 1.28; range, 5.58-9.44). IPT binding ratios (mean ± SD) were significantly lower in patients with Hoehn and Yahr stage II (ipsilateral striatum: 3.47 ± 0.75; contralateral striatum: 2.96 ± 0.73) compared with those with Hoehn and Yahr stage I (ipsilateral striatum: 4.72 ± 0.75; contralateral striatum: 3.69d ± 0.61) (P<.001). The ipsilateral striatum of patients with Hoehn and Yahr stage I showed a significant mean ± SD reduction of IPT binding (ipsilateral striatum: 4.72 ± 0.75) compared with either right or left striatum of controls (P<.001). Only in 1 patient was IPT binding to the ipsilateral striatum (ratio, 6.40) higher than the lowest value observed in the striatum of a control subject (ratio, 5.58).

Conclusions

Use of [I-123]IPT and single photon emission computed tomography demonstrates a reduction of dopamine transporter binding in patients with early Parkinson's disease. Significantly reduced IPT binding already observed in the ipsilateral striatum of patients with Hoehn and Yahr stage I demonstrates the potential of this method to detect preclinical disease.