Presynaptic nigro-striatal function in a group of Alzheimer's disease patients with parkinsonism: evidence from a dopamine transporter imaging study

The occurrence of parkinsonism in Alzheimer's disease (AD) is quite common, however the molecular and neurochemical changes underlying such extrapyramidal features in AD have been not fully understood. Post-mortem as well as in vivo imaging study have produced conflicting results as regards the existence of dopaminergic changes in AD. Aim of the present study was to investigate in vivo the nigro-striatal dopaminergic function in a group of AD patients with parkinsonism. Thirteen patients with AD and extrapyramidal features not related to past neuroleptic use (AD-P) underwent SPECT with I-123-FP-CIT, a ligand of dopamine transporter, and the data were compared with those obtained in 15 patients with Diffuse Lewy Body Dementia (DLBD), 20 patients with Parkinson's disease (PD), and 8 healthy elderly controls. The analysis of the data was performed by regions-of-interest approach and calculations of the striatal-to-non specific (occipital lobes) radioactivity ratios were made. The I-123-FP-CIT striatal uptake in patients with AD-P was similar to that obtained in the control population. Both the DLBD and PD groups showed significantly lower I-123-FP-CIT uptake in all striatal areas with respect to AD-P and control groups (p<0.005). The lack of dopamine transporter changes in our series of AD-P patients can indicate that dopaminergic presynaptic function is preserved in this population and that different dopaminergic changes such as postsynaptic ones, or different neurotransmitter alterations might underlie the extrapyramidal features in AD.