Objective: To assess feasibility of identifying SN involvement on DaTi, correlate with laterality of motor symptoms and compare with loss of nigrosome-1 hyperintensity on SWI .

Background: Dopamine transporter is decreased in Parkinson’s disease(PD)and Parkinsonian syndromes(PS). Tc99mDaTSPECTimaging(DaTi) is an effective way of diagnosis of degenerative PS.It correlated well with the laterality of the dominant side of motor symptoms(DMS). Its often difficult to differentiate PD from PS,as the tracer uptake patterns vary with stage of disease(1).Susceptibility weighted imaging (SWI) based identification of loss of nigrosome-1 hyperintensity (n1H),known as swallow tail sign(STS)within substantia nigra (SN) on MRI has shown to have excellent utility in diagnosis of PD,differentiating it from PS and also correlates well with laterality of DMS(2).We hypothesized that the SN decreased tracer binding (DTB) can also be assessed visually on DaTi.The correlation of same was done with the abnormal SN on MRI.

Method: Retrospective study of 3-year database from Jan 2017-20.Only those patients with DaTi and MRI were selected.A total of 26 patients were identified and images analyzed visually.In DaTi, the presence SN DTB was documented based on the side, basal ganglia(BG) DTB asymmetry was documented.SWI images were analyzed for presence or absence of n1H and the laterality of the finding was documented.Out of these 17 had clinical details with documented side of DMS and only these were selected for correlation with DMS and abnormal SN on SWI.Correlation analysis was done by R statistical analysis software.

Results: Median age 65 (9 female and 6 male).Median duration of symptom was 12months.Dominant symptomatic side in patients was right(9), left(4), bilateral(4).In DaTi SN DTB was not clearly delineated in(2), right(6) and left(8)and bilateral(1).The BG DTB was right (11), left (4) and bilateral(2).In SWI, STS was on left(10), bilateral(2)and the n1H was maintained in 5 patients despite having abnormal DaTi.On correlation for laterality of symptoms between these modalities and DMS concordance was found in 11(73.3%) and discordance in 4(26.7%).

Conclusion: SN DBT can be identified visually on DaTi done for PS disorders and its correlates well with STS on SWI images and clinical side of dominant symptom.This feasibility study paves way for further research with larger sample size for this novel imaging finding.

References: Esmaeili A, Beiki D, Oveisgharan S, et al. Evaluation of 99mTc-TRODAT-1 SPECT in the diagnosis of Parkinson’s disease versus other progressive movement disorders. Ann Nucl Med. 2016 Feb;30(2):153–62. Imaging the Nigrosome 1 in the substantia nigra using susceptibility weighted imaging and quantitative susceptibility mapping_ An application to Parkinson’s disease | Elsevier Enhanced Reader [Internet]. [cited 2020 Feb 28].

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MDS Abstracts - https://www.mdsabstracts.org/abstract/substantianigral-involvement-on-tc99mdatspect-a-novel-and-under-recognised-imaging-finding-in-parkinsonian-disorders/