Comparison between odor discrimination, substantia nigra echogenicity and nigrostriatal dopaminergic activity measured by 18F.PR04 pet in Parkinsonian syndromes

Abstract

Objective: To evaluate the relationship between odor discrimination, substantia nigra echogenicity and nigrostriatal dopaminergic activity in patients with Parkinson ' s disease. Background: Positron emission tomography for imaging dopaminergic pathways, transcranial substantia nigra (SN) echogenicity and odor discrimination are used as complementary tools for the diagnosis of PD. However there is a lack of information about the relationship between these three diagnostic methods for helping in the diagnosis of PD. Methods: Twelve patients with PD according to established criteria were prospectively included. All subjects underwent a dynamic PET scan (Siemens mCT) for a duration of 2 h after bolus injection of 165 ± 15 MBq (mean ± SD) [18 F]PR04.MZ. Data analysis using noninvasive Simplified Reference Tissue Model (SRTM) method and Cerebellum as reference was performed for estimation of binding potential in different brain regions. Odor discrimination was evaluated by using sniffing stick test (hyposmia < 7 detections) and transcranial sonography of the SN was also conducted. Pathological echogenicity was considered as SN area more than 0.20 cm2. Study was approved by local and governmental authorities and participants signed informed consent. Results: Age (mean +/−SD) was 56.8 +/−13.9 years. Substantia nigra hyperechogenicity was found in 10 patients (SN area: 28.8 +/−14.2). Hyposmia was observed in 6 cases (7.5 +/−3 odors). PET analyses showed dopaminergic depletion in 11 patients. Percentage of Posterior putamen depletion was 66.0 +/−29.2. Nine subjects with Dopaminergic depletion also exhibited SN hyperechogenicity. There was no relationship between SN area or olfaction detection and magnitude of dopaminergic depletion. Conclusions: Evaluation of SN echogenicity and dopaminergic activity by 18FPR04.MZ PET are valuable tools in the diagnosis of PD. Larger studies are required to confirm these findings. SUPPORTED BY FONDECYT No. 11130534.