Effect of age on caudate dopaminergic function in idiopathic Parkinsonism.

Aging has long been implicated in the pathogenesis of Idiopathic Parkinsonism (IP). However, postmortem studies have demonstrated that the pathological changes in aging and IP affect the dopaminergic function in putamen and caudate nuclei differently. This has been considered by some authors as evidence against the role of aging in IP. We performed fluorodopa (FD) positron emission tomography (PET) in 36 patients with IP and 25 normal controls to test the hypothesis that the effect of aging on the striatal dopaminergic function in IP differs from the effect of aging in normal controls. We found that the FD uptake constant (Ki) in the caudate nucleus of patients with IP declines with both age (p = 0.002) and duration (p = 0.05) of symptoms. This effect was over and above that of normal aging (p = 0.007). We did not find a similar superimposed effect of age in the putamen. We conclude that the effect of aging on the dopaminergic function in the caudate nucleus in IP differs from that in normal aging. Whether this abnormal aging precedes and even predisposes to IP or is triggered by pathogenetic factors in IP is unclear.