Cognition in Patients With a Clinical Diagnosis of Parkinson Disease and Scans Without Evidence of Dopaminergic Deficit (SWEDD): 2-Year Follow-Up

Objective and Background: More than 10% of patients clinically diagnosed with Parkinson disease demonstrate normal dopamine uptake on dopamine transporter single-photon emission computed tomography (DaTscan), but little is known about how cognitive function differs between patients with dopamine deficiency on DaTscan and patients with scans without evidence of dopaminergic deficit (SWEDD). We compared the cognitive function of these two groups of patients over 2 years. Methods: We retrospectively analyzed data obtained from the Parkinson's Progression Markers Initiative on 309 participants clinically diagnosed with idiopathic Parkinson disease who had scored in the normal range on the Montreal Cognitive Assessment at baseline and had completed 1- and 2-year follow-up visits. We compared the Montreal Cognitive Assessment scores at 1 and 2 years between the 42 participants with SWEDD and the 267 with dopamine deficiency. Results: Mean cognitive scores did not differ significantly between groups at 1 year, but at 2 years the participants with SWEDD performed more poorly. At 2 years, 31% of the participants with SWEDD versus 15% of those with dopamine deficiency had statistically reliable cognitive impairment. Conclusions: This study provides evidence that some individuals clinically diagnosed with idiopathic Parkinson disease but with SWEDD demonstrate early cognitive decline. The results also suggest that recently diagnosed patients with SWEDD may be at even greater risk for cognitive decline than patients with DaTscan-confirmed early-stage Parkinson disease. While patients with SWEDD likely represent a heterogeneous group of etiologies, our results highlight the need to monitor these patients' cognitive function over time.