Sleepiness, parkinsonian features and sustained attention in mild Alzheimer's disease

Background: we previously demonstrated that patients with mild Alzheimer's disease and parkinsonian features (AD + PF) are at a higher risk of having daytime sleepiness than mild AD patients without PF (AD - PF). Objective: to determine whether AD + PF patients demonstrate a known a consequence of daytime sleepiness, reduced performance-based sustained attention, compared with AD - PF patients. Methods: a nocturnal polysomnogram and a next-day multiple sleep latency test (MSLT) were performed. Between MSLT nap opportunities, a 10-min psychomotor vigilance test (PVT) was administered and analysed for reciprocal mean response times (IMEAN), number of lapses (LAPSE) and reciprocal mean slowest 10% (ISLOW). Results: a total of 35 patients met criteria (AD + PF, n = 16; AD - PF, n = 19). Comparatively, the AD + PF group had slower IMEAN results [F-(1,F-28) = 6.64, P < 0.05] and higher LAPSE rates [F-(1,F-27) = 7.57, P < 0.05]. ISLOW measures were not different between groups. When accounting for MSLT results, IMEAN and LAPSE results were no longer significantly different between groups during morning tests, but remained significantly different on afternoon tests. Conclusion: PFs in mild AD are associated with decreased sustained attention as measured by the PVT. Sleepiness did not fully account for the impairment in sustained attention, suggesting that the presence of PFs has an independent negative association with sustained attention in mild AD.