Studying cognitive function in patients with a long-standing diagnosis of SWEDD.

Introduction: The cognitive profile of patients with longstanding clinical Parkinsonism possessing scans without evidence of dopaminergic deficit (SWEDD) remains unclear from previous studies.

Methods: We studied 47 patients recruited in the Parkinson's Progression Markers Initiative with SWEDD as baseline diagnosis. They were subdivided by final clinical diagnoses after a 2-year follow-up period into 25 patients with either clinical evidence of Parkinson's Disease (PD) or unclassified parkinsonism and normal SPECT imaging ("true SWEDDs"), 6 patients with a psychogenic illness exhibiting Parkinsonism, 6 patients who had phenoconverted to PD based on reduced striatal dopaminergic activity on imaging, and 10 patients with another tremulous condition. Cognitive symptoms were compared between these subgroups, as well as with 62 PD patients and 195 healthy controls (HCs), at baseline and follow-ups.

Results: A significant difference in working memory was found between true SWEDDs and HCs (P = 0.009), but not true SWEDDs and PD patients (P = 0.432), nor PD patients and HCs (P = 0.154). The prevalence of attentional impairment was also significantly different between the three groups (P < 0.001). SWEDD subgroups possessed similar cognitive symptoms irrespective of their final clinical diagnosis. Psychogenic, phenoconverted and tremulous SWEDDs also possessed stable cognitive symptoms over the 2-year period whilst true SWEDDs, PD patients and HCs experienced significant changes in working memory.

Conclusions: Our results, particularly relating to working memory and attention, add to the knowledge of other true SWEDD non-motor symptoms to facilitate earlier diagnosis and improved management strategies for these patients.