Imaging of dopamine transporters with [I-123]FP-CIT SPECT does not suggesta significant effect of age on the symptomatic threshold of disease in Parkinson's disease

Parkinson's disease (PD) is characterized neuropathologically by degenerati on of the nigrostriatal dopaminergic pathway. With natural aging there is l oss of dopaminergic cells in the substantia nigra and, consequently, loss o f dopamine transporters in the striatum. It has been suggested that PD is c aused by an accelerated rate of cell death. Conceptually, symptoms in idiop athic PD become apparent after a critical level of cell loss, the "symptom threshold." It has been suggested that this symptom threshold is independen t of age. In this study, [I-123]FP-CIT SPECT was used to assess the effect of aging on the density of striatal dopamine transporters in vivo in contro ls (n = 36) and early, drug-naive, patients with PD (n = 32). We found a si gnificant age-associated decline of [I-123]FP-CIT binding to striatal dopam ine transporters in controls, but not in parkinsonian patients. This findin g might give further support for the existence of an age-independent thresh old in PD. In a subgroup of patients with hemi-PD, we found a significant l oss of dopamine transporters bilaterally in the caudate nucleus and putamen . This loss was more pronounced in the putamen than in the caudate nucleus and the contralateral binding was significantly lower than the ipsilateral binding. By using age-corrected data, we estimated that in our particular p atient group motor signs started when the loss of [I-123]FP-CIT binding rat ios in the putamen was 46-64%. (C) 2001 Wiley-Liss, Inc.