Hallucinations and sleep-wake cycle in Alzheimer's disease: a questionnaire-based study in 218 patients

The aim was to evaluate the relationship between hallucinations and the sleep-wake cycle in a sample of Alzheimer's disease (AD) patients in the early-moderate stage. Two hundred and eighteen AD patients (66 males, 152 females, mean age 74.3+/-6.85) were administered a sleep questionnaire in the presence of a care-giver. Twenty-six out of 218 (12%) reported the occurrence of hallucinations, mainly visual. In 18/28 (69%) hallucinations occurred when the patient was awake and in 8 (31%) hallucinations were reported to occur close to a specific phase of the sleep-wake cycle. Vivid dreams were reported in 25/218 (11%) and violent sleep-related and dream-related behaviours (probable REM behaviour episodes) in 22/218 (10%). Both REM phenomena were more frequent in AD hallucinators than in AD non-hallucinators (26.9% vs. 9.3%, and 26.9% vs. 7.8%, p<0.007). Our data indicate a lower incidence of hallucinations and presumable REM behaviour disorder (RBD) in AD, at least in the early-moderate phase, than that observed in synucleinopathies. However, the higher occurrence of vivid dreams and RBD in AD patients with hallucinations compared to those without hallucinations indicates a potential role of disordered REM sleep in influencing the occurrence of hallucinations in AD, similar to what has been observed in synucleinopathies.