Sleepiness at the Time of Testing Impairs Olfactory Performance

We aimed to investigate the differential roles of hypocretin versus dopamine dysfunction versus excessive daytime sleepiness (EDS) in the development of hyposmia. Olfaction in patients with Parkinson disease, restless leg syndrome, narcolepsy with cataplexy, EDS, and healthy controls was compared.Sixty-six subjects participated in the study: 14 with PD, 13 with NC, 12 with RLS, 8 with EDS, and 20 healthy controls. Olfaction was tested using standardized Sniffin'Sticks test. Sleepiness was assessed using Karolinska, Stanford and Epworth sleepiness scales.Olfactory discrimination correlated negatively with subjective momentary sleepiness. A significant deficit in olfaction was found in PD patients with respect to all other groups in all olfactory domains. No significant differences were found between the other groups.We could not confirm decreased olfaction in patients with NC. Yet the significant correlation between momentary sleepiness and olfactory function suggests that sleepiness is a potential confounding factor in the assessment of olfaction, e.g. in NC. Furthermore, our results confirm that olfaction is impaired in PD, whereas it is normal in RLS.