Olfactory hallucinations in Alzheimer's disease.

We assessed the frequency, duration, and degree of unpleasantness of olfactory hallucinations in Alzheimer's disease (AD). Informants of 31 AD patients were invited to rate the frequency, duration, and degree of unpleasantness of olfactory, auditory, and visual hallucinations. Analysis demonstrated little occurrence of olfactory hallucinations compared with auditory or visual hallucinations. Results also demonstrated that olfactory hallucinations span from a few seconds to one minute, a duration that was similar to that of auditory and visual hallucinations. Olfactory hallucinations were rated as unpleasant compared with auditory or visual hallucinations. Finally, olfactory hallucinations were significantly correlated with depression. Our findings demonstrate little occurrence of olfactory hallucinations but that when they occur, they are experienced as relatively unpleasant in AD patients. Our findings also demonstrate a relationship between olfactory hallucinations and psychiatric characteristics (i.e., depression) in AD.