Striatal dopamine transporter binding assessed by [I-123]IPT and single photon emission computed tomography in patients with early Parkinson's disease - Implications for a preclinical diagnosis

Background: Specific binding to dopamine transporters may serve as a tool t o detect early loss of nigrostriatal dopaminergic neurons in patients with Parkinson's disease. Objective: To determine striatal dopamine transporter binding using the coc aine analogue [I-123]N-(3-iodopropen-2-yl)-2 beta-carbomethsxy-3 beta-(4- c hlorophenyl) tropane ([I-123]IPT) and single photon emission computed tomog raphy. Patients and Methods: We studied 9 control subjects (mean age, 58 years; ra nge, 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 tomog raphy was performed 90 minutes after injection of 120 to 150 MBq of radioac tive [I-123]IPT. Results: Specific striatal [I-123]IPT binding (mean +/- SD) was significant ly 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; r ange, 1.80-5.13) compared with controls (left striatum: 7.28 +/- 0.94; rang e, 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 Y ahr 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: 3.69 +/- 0.61) (P<.001). T he ipsilateral striatum of patients with Hoehn and Yahr stage I showed a si gnificant mean +/- SD reduction of IPT binding (ipsilateral striatum: 4.72 +/- 0.75) compared with either right or left stria rum of controls (P<.001) . Only in 1 patient was IPT binding to the ipsilateral striatum (ratio, 6.4 0) higher than the lowest value observed in the striatum of a control subje ct (ratio, 5.58). Conclusions: Use of [I-123]IPT and single photon emission computed tomograp hy demonstrates a reduction of dopamine transporter binding in patients wit h early Parkinson's disease. Significantly reduced IPT binding al ready obs erved in the ipsilateral striatum of patients with Hoehn and Yahr stage I d emonstrates the potential of this method to detect preclinical disease.