Objective: To examine the clinical and biological characteristics of participants with scans without evidence of dopaminergic deficit (SWEDD) during a two-year follow-up.

Background: Study participants with SWEDD at screening DAT imaging have clinical and imaging progression inconsistent with typical PD. DAT imaging has been increasing utilized as an eligibility criterion in PD clinical trials to enrich the study cohort for PD pathology.

Method: The Parkinson’s Progression Markers Initiative (PPMI) is an observational longitudinal study of progression biomarkers for PD.  Untreated PD participants were required to have abnormal DAT scan (visual read) for enrollment. Participants with the investigator diagnosis of PD and SWEDD were followed prospectively for 2 years as a separate cohort. All SWEDD participants were assessed with motor and non-motor scales, repeat DAT imaging and biologic variables. DAT imaging was assessed both visually and with quantitative analysis. Specific binding ratio (SBR) < 65%, >=65 to <80% and >=80% of age expected lowest putamen were used as cut offs for PD, indeterminate and non-PD quantitative classification respectively].

Results: 16% of PD subjects were SWEDDs (81/503). 64/81 SWEDDs were enrolled in follow up. At baseline there was no age/ gender, disease duration difference between SWEDDs and PD subjects. SWEDDs had lower MDS-UPDRS Part III scores and higher part I scores. At baseline, 4/81 participants with SWEDD on visual read had <65% age expected lowest putamen SBR. Two-year scans were completed in 51/64 participants with SWEDD.  At two years 4/51 had <65% age expected lowest putamen SBR (2 had baseline <65 and 2 had baseline indeterminate).  At two years 5 participants had a positive visual read (including all 4 of those with <65% at 2 years). [TS1]80 or 81?

Conclusion: There is approximately a 5% variance between visual and quantitative definition of SWEDDs suggesting that a visual/quantitative hybrid may provide the best accuracy. In this study, when readers were required to have very high certainty of DAT deficit at visual read at baseline approximately 5% of subjects defined as SWEDD had a DAT deficit at 2-year follow-up.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/clinical-and-dat-imaging-characteristics-of-participants-with-scans-without-evidence-of-dopaminergic-deficit-swedds-ppmi-cohort-2-year-follow-up/