Objective: To examine the clinical characteristics of SWEDDs and to compare to that of Parkinson’s disease (PD).

Background: Patients with SWEDDs are defined as clinically diagnosed PD ones with normal nigrostriatal presynaptic dopaminergic tracer imaging. The frequency of SWEDDs has been reported to be about 5-20% of clinically diagnosed PD patients. In Japan, DAT scintigraphy using FP-CIT has been available to use from 2014 and SWEDDs patients have been being identified in our hospital.

Methods: We enrolled 174 clinically diagnosed PD patients. SWEDDs is defined as fulfilling the following three criteria; 1: Average Specific binding ratio (SBR) is more than 3.5, 2: Asymmetry Index is less than 15% and 3: striatal FP-CIT accumulation is normal by visual assessment judged by three neurologists who are familiar with DAT scintigrapgy.

We examined clinical characteristics and ancillary diagnostic tests including age at onset, duration, Hoehn-Yahr(H-Y) stage, UPDRS score, H/M ratio of MIBG cardiac scintigraphy, olfactory function by OSIT-J test, ACE-R, and an existence of REM sleep behavior disorder (RBD) or depression.

Results: In clinically diagnosed 174 PD patients, 14 patients (8.5%) are diagnosed as having SWEDDs. H-Y stage of SWEDDs was lower than that of PD (2.0 vs 2.25) (p=0.001). Mean SBR of SWEDDs was significantly higher than that of PD (4.56 vs 2.16) (P=0.001). Early and delayed H/M ratios of SWEDDs were significantly higher than those of PD, respectively (2.64 vs 1.93, 2.78 vs 1.59) (p=0.002). Three of 14 SWEDDs patients had decreased H/M ratio and one of whom had RBD. SBR in SWEDDs is significantly correlated with age (r=-0.874, P=0.001) and delayed H/M ratio (r=0.574, P=0.032).

Conclusions: The frequency of SWEDDs in clinically diagnosed PD patients was 8.5% and was similar to the previous reports. In most of SWEDDs patients, motor symptoms were weak and H/M ratios were within normal limit, in contrast to the findings in PD. These results suggest that the pathophysiological status of SWEDDs is different from that of PD. However, the presence of the patient with both decreased MIBG uptake and RBD in SWEDDs patients suggests that early phase of PD patients can exist in SWEDDs patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/clinical-characteristics-of-scan-without-evidence-of-dopaminergic-deficits-swedds-in-japan/