Scan without evidence of dopaminergic deficit (SWEDD) in degenerative parkinsonism and dementia with Lewy bodies: A prospective study

Background I-123-FP-CIT SPECT imaging is a reliable method to assess presynaptic dopaminergic pathways in degenerative parkinsonisms and dementia with Lewy bodies (DLB). Methods: We aimed at examining sensitivity of combined visual and semi-quantitative I-123-FP-CIT SPECT analyses in a prospective cohort of subjects with DLB and degenerative parkinsonisms - Parkinson's disease (PD), multiple system atrophy (MSA), corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP) to determine prevalence and clinical significance of scans without evidence of dopaminergic deficit (SWEDD). 372 scans performed from 2013 to 2016 with the same SPECT acquisition and processing protocol were analyzed. We identified 155 patients with degenerative parkinsonism and 53 with DLB. Diagnoses relied on validated clinical criteria for each condition. Semi-quantitative assessment was based on previously established local reference limits (including striatal volumes of interest uptake, caudate-to-putamen ratio and striatal asymmetry index). Results: 3/155 (2.1%) subjects with degenerative parkinsonism (1 CBS, 1 MSA-C and 1 PD) and 1/53 (1.9%) with DLB had a normal visual SPECT. Subsequent semi-quantitative analysis showed mild striatal uptake impairment for the DLB and the PD subject. Therefore, only two patients (1 CBS and 1 MSA) had a strictly normal combined assessment. Conclusions: The present study shows that SWEDD cases represent a negligible proportion of patients with degenerative conditions (1.3%), when stringent diagnostic criteria are applied, a thorough follow-up is performed and visual SPECT analysis is combined with precise semi-quantitative assessment.