King's College London

Objectives/Background Excessive daytime sleepiness (EDS) is a common disorder, which can manifest in isolation or in combination with other neurological or psychiatric disorders. We know relatively little about the mechanisms underlying the development of EDS and the clinical management of patients with EDS remains an unmet need. In this study, we hypothesised that thalamic dopaminergic function would be altered in subjects with EDS and we sought to investigate this by assessing [123I]FP-CIT Single Photon Emission Computed Tomography (SPECT) data, which is a molecular imaging marker of dopamine transporter (DAT). Patients/Methods We performed a case-control study using people registered as healthy subjects in the Parkinson’s Progression Markers Initiative database. We assessed and compared semi-quantified identified [123I]FP-CIT-SPECT in two groups of 21 healthy subjects with and without EDS, who were matched for age, gender, age of diagnosis, years of education and disease duration. Results Our findings show increased thalamic DAT binding in people with EDS compared to matched healthy subjects without EDS. Higher thalamic DAT binding also correlated with worse EDS scores. Conclusion Our findings provide evidence that increased dopaminergic function in the thalamus may mediate excessive daytime sleepiness in humans.