Objective: To investigate the simple parameter by which fully represent the level of nigral dopamine in putamen by means of routine 18F-FP-CIT positron emission tomography (PET) data in Parkinson’s disease (PD).

Background: Dopaminergic neuronal degenerations, the pathologic hallmark of Parkinson’s disease (PD), are well known to progress from ventrolateral to medial region of substantia nigra, which lead to more predominant loss of dopamine in posterodorsal area of putamen compared to that of anteroventral area. A semiquantitative analysis of nigral dopaminergic neurons via volumetric assessment of dopamine transporter imaging is useful to investigate the severity of dopaminergic loss and their relationship to a variety of clinical parameters in patients with PD. Unfortunately, this approach requires much more time intensive process and is not easy to be performed routinely in clinical practice. We set to investigate the simple parameter by which fully represent the level of nigral dopamine in putamen by means of routine 18F-FP-CIT positron emission tomography (PET) data in PD.

Methods: This study included subjects with de novo PD (n = 21) and drug induced parkinsonism (DIP) (n = 17) who underwent 18F-FP-CIT PET scan at their initial workup. All the PET images were analyzed with volume-of-interest of putamen and caudate nucleus, and subsequently nondisplaceable binding potential (BPND) were calculated. To estimate the ratio of putamen-to-caudate nucleus, the maximum diameter of caudate head (A) and a length from the mid point of caudate head diameter to the visually defined extreme posterior pole of putamen (B) were measured at mid thalamic level of axial plane, . Then, the ratio of “B/A” was estimated.

Results: The mean values of putamen-to-caudate ratio in PD were lower than those in DIP on both side (right, 1.16 vs 2.58, p < 0.001; left, 1.15 vs 2.6, p < 0.001). The putamen-to-caudate ratio showed strong associations with BPND of putamen in either more affected (r = 0.805, p < 0.001) and less affected side (r = 0.797, p < 0.001) in PD, respectively. 

Conclusions: Our study suggests the putamen-to-caudate ratio as a simple and reliable surrogate marker for dopaminergic volume of putamen, which might be a useful tool to easily estimate the severity of dopaminergic loss in PD in clinical practice.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-putamen-to-caudate-nucleus-ratio-a-simple-surrogate-marker-for-dopaminergic-volume-in-putamen/