Olfactory recognition deficit in Alzheimer's and Parkinsonian dementias

The central olfactory apparatus is adversely affected by the pathological changes of Alzheimer's disease (AD) and Parkinsonian dementia (PD). We investigated the ability to recognize odors (using a 20 item forced choice paradigm variant) in these diseases compared to normal subjects, demented alcoholics and non-demented alcoholics over a wide age range. Stimuli used were 10 pairs of strong smelling common odorants (e.g.: garlic and onion). Subjects were also tested with the Guild Memory Scale to establish disease stage (GDS) or normal memory for age. Potential subjects with substantial verbal comprehension deficits were eliminated by a control task. Results were that the AD and PD patients, whose performance was statistically equivalent and close to chance, performed significantly worse than all other groups (whose scores were all close to 100% correct) by one way ANOVA. An ANCOVA with GDS and age as covariates confirmed the effect of diagnosis per se on olfactory recognition performance (p=.015).