Long-term follow-up study of SWEDD patients with mild parkinsonian signs.

Background: Whether scan without evidence of dopaminergic deficit (SWEDD) can be a reliable indication of a clinical entity of Parkinson's disease (PD) is controversial. Objective: To evaluate the proportion of SWEDD patients with mild parkinsonian signs who are classifiable as idiopathic PD. Methods: 32 SWEDD patients with unilateral or asymmetric finger tremor with a rest component and unilateral rigidity (Unified Parkinson's Disease Rating Scale (UPDRS)-III scores of 3-5) were enrolled. They underwent longitudinal examination by UPDRS-III, Mini-Mental State Examination (MMSE), smell test and Results: At follow-up, 21 of 32 SWEDD patients (65.6%) showed significantly reduced specific binding ratios below the normal range, that is, positive DaTSCAN, sometimes with increased asymmetry index (n=11). Among these 21 patients, the mean (SD) UPDRS-III score at follow-up was significantly higher than that at baseline (5.5 (2.2) vs 4.0 (0.5)) (p=0.003). The mean (SD) MMSE scores in SWEDD patients (n=32) at baseline and follow-up were not significantly different compared with those in controls. Olfactory function both in SWEDD patients with positive and negative DaTSCAN was significantly impaired versus controls (p<0.001), although no significant difference was recognised between patients with positive (n=21) and negative (n=11) second DaTSCAN. Conclusion: The majority of SWEDD patients with mild rest tremor and rigidity could be classified as having idiopathic PD in this longitudinal and long-term follow-up study.