Association of daytime sleepiness with nigrostriatal dopaminergic degeneration in early Parkinson's disease

Abstract

Many patients with Parkinson's disease (PD) report daytime sleepiness. Its etiology, however, is still not fully understood. The aim of this study was to examine if the amount of nigrostriatal dopaminergic degeneration is associated with subjective daytime sleepiness in patients with PD. We investigated 21 patients with PD clinically and by means of [(123)I] FP-CIT-SPECT (DaTSCAN(R)). Each patient filled in the Epworth sleepiness scale (ESS), the Parkinson's Disease Sleep Scale (PDSS), and the self-rating depression scale according to Zung (SDS) to assess sleepiness, sleep quality, and depressive symptoms. The mean specific dopamine transporter binding in the 21 PD patients (60.8 +/- 10.4 years, nine females, median Hoehn and Yahr stage 2.0) was decreased. Nine patients were in Hoehn and Yahr stage 1 (58.7 +/- 6.6 years, four females; ESS score 7.4 +/- 4.5; PDSS score 105.1 +/- 30.9), the other 12 patients were in Hoehn and Yahr stage 2 (62.4 +/- 12.6 years, five females; ESS score 6.7 +/- 4.7, PDSS score 97.1 +/- 25.6). Age, gender, ESS, and PDSS scores were not significantly different in both groups. However, ESS scores showed an inverse correlation with mean DAT binding in the striatum (r = -0.627, p = 0.03), the caudate nucleus (r = -0.708, p = 0.01), and the putamen (r = -0.599, p = 0.04) in patients with Hoehn and Yahr stage 2. There was no correlation of the ESS score with age, disease duration, UPDRS motor score, PDSS score, or depression score. Subjective daytime sleepiness seems to be associated with dopaminergic nigrostriatal degeneration in early PD.