Objective: To investigate the relationship between hypothalamic D3 dopamine receptor availability and severity of sleep problems in Parkinson disease (PD).

Methods: Twelve patients were assessed with PET and the high-affinity dopamine D3 receptor radioligand [11C]-propyl-hexahydro-naphtho-oxazin ([11C]-PHNO). Severity of sleep problems was rated with appropriate subitems of the Unified Parkinson's Disease Rating Scale part I (patient questionnaire) and the Epworth Sleepiness Scale.

Results: We found that lower dopamine D3 receptor availability measured with [11C]-PHNO PET was associated with greater severity of excessive daytime sleepiness but not with problems of falling asleep or insomnia.

Conclusion: In our cohort of patients with PD, the occurrence of excessive daytime sleepiness was linked to reductions in hypothalamic dopamine D3 receptor availability. If these preliminary findings are confirmed in larger cohorts of patients with polysomnographic characterization, selective pharmacologic modulation of the dopaminergic D3 system could be used to increase daytime alertness in patients with PD.