Striatal dopamine uptake and olfactory dysfunction in patients with early Parkinson's disease

Olfactory dysfunction is a sensitive biomarker of neurodegeneration and a cardinal premotor symptom of Parkinson's disease (PD). Although several non-motor symptoms of PD have been correlated with decreased dopamine transporter uptake, olfactory dysfunction and reduced dopamine transporter uptake have not been widely investigated in PD. In this study, we aimed to identify the dopamine transporter status of the corpus striatum and thalamus using a magnetic resonance imaging (MRI)-guided spatial normalization method in patients with PD according to olfactory function.

Among 87 PD patients, 50 had hyposmia and 37 had normosmia. All patients underwent positron emission tomography (PET) using ¹⁸F-N-(3-fluoropropyl)-2beta-carbon ethoxy-3beta-(4-iodophenyl) nortropane (¹⁸F-FP-CIT) and T1-weighted MRI. PET images were normalized with simultaneously performed spatially normalized MRI and the regional standardized uptake value ratios (SUVR) with a volume of interest template were compared according to olfactory function.

The bilateral caudates and the left anterior and posterior putamen of the hyposmic group showed significantly reduced dopamine transporter uptake compared to the normosmic group. In partial correlation coefficient analysis, olfactory identification impairment was correlated with the SUVR values of the caudate nuclei.

More dopaminergic impairment of the bilateral caudate nuclei was found in hyposmic PD. This finding suggests that decreased dopamine uptake in the caudate nucleus may be an imaging trace of olfactory dysfunction in patients with PD.