Minimal parkinsonism in the elderly is associated with striatal dopamine loss and pontine structural damage

Introduction: To investigate whether neurodegeneration underlying Parkinson's disease (PD) accounts for a substantial proportion of cases of minimal parkinsonism in the elderly. Methods: We recruited 48 consecutive subjects with minimal parkinsonism who visited the clinic with cognitive complaints. All subjects did not show findings compatible with PD on ¹⁸F-FP-CIT PET scans, and had no evidence of other neurodegenerative disorders. Striatal dopamine transporter (DAT) availability was quantified, and mean diffusivity (MD) values in the pons were calculated to characterize structural damage using diffusion tensor imaging. Additionally, 35 patients with PD and 21 healthy controls were included as reference groups. Results: Individuals with minimal parkinsonism (mean age, 73.23 ± 7.03 years) exhibited mild decrease in DAT availability in the posterior putamen, which was at a level between that of healthy controls and patients with PD. DAT availability in the caudate and anterior putamen was also mildly decreased in the minimal parkinsonism group. Individuals with minimal parkinsonism also tended to have higher MD values in the pons compared to healthy controls. Conclusions: Our results suggest that a substantial proportion of minimal parkinsonism is associated with nigrostriatal dopamine depletion and pontine structural damage, which may be related to the disease process of prodromal PD.