Objective: To investigate the differences and similarities between SWEDD patients and PD patients using smell test.

Background: The concept of SWEDD(scans without evidence of dopaminergic deficit) originates from the clinical trial literature for Parkinson’s disease (PD). Some debate that SWEDDS contain various disease spectrums (idiopathic PD, essential tremor, dystonic tremor, and other parkinsonism). There is only one report about olfactory function in patients with SWEDD. Hyposmia occurs in 80-100% of PD cases, and because smell identification in SWEDD is normal or only mildly decreased, smell tests have also been suggested as a way to help distinguish PD from SWEDD.

Methods: Parkinson’s disease patients were enrolled at movement disorders center. This study enrolled 28 patients with SWEDDs (bradykinesia with decremental response (SWEDD-A) = 17, bradykinesia without decremental response (SWEDD-B)=11), 35 patients with PD and 14 healthy controls. KVSS (Korean version of Sniffin stick test) has been performed on all subjects for evaluation of olfactory function, and parameters including threshold, discrimination and identification were compared among the all groups.

Results: The mean total, threshold, discrimination and identification scores in the PD group were the lowest of the three groups. Smell test scores in the SWEDD group were not significantly difference from that of PD or control. But intermediate scores of smell tests in the SWEDD patients is defined between PD and control. Additionally, in subgroup of SWEDD, the mean threshold and total scores in the SWEDD-A were significantly lower than that of control group.

Conclusions: The intermediate status of smell test in the SWEDD patients in our study may have been due to the heterogeneity of the SWEDD patients. In SWEDD group, olfactory dysfunctions of SWEDD-A are more close to the PD group, and SWEDD-B is more close to the control group. In sight of olfactory dysfunction as prodromal nonmotor features of PD, patients with SWEDD-A might be convert to PD more than patients with SWEDD-B, although clinically and dopamine transporter imaging follow up studies will be needed. To conclude, in common with PD, SWEDD with Parkinsonian bradykinesia symptoms tended to have olfactory dysfunction, but not in SWEDD without Parkinsonian bradykinesia. So smell test could not distinguish between PD and SWEDD, because of heterogeneity of SWEDD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/could-smell-test-differ-from-scans-without-evidence-of-dopaminergic-deficit-and-parkinsons-disease/