OLFACTION IN NEURODEGENERATIVE DISEASE - A METAANALYSIS OF OLFACTORY FUNCTIONING IN ALZHEIMERS-AND-PARKINSONS-DISEASES

Background: Olfactory deficits in Alzheimer's disease (AD) and idiopat hic Parkinson's disease (PD) have been well established. Objective: To clarify and review the literature by evaluating the evidence for olfa ctory deficits in 3 olfactory domains, including odor identification, recognition, and detection threshold. Data Sources: A literature searc h of English-language studies of olfaction in AD, PD, and healthy cont rols was conducted via online databases (PsycInfo and MEDLINE) and ref erence lists from review articles. Study Selection: To meet selection criteria for metaanalysis, each study required a control group and com plete and usable data. This review yielded 26 publications of olfactor y identification, recognition, and/or detection threshold. Because of the inclusion of more than 1 relevant study of olfaction in several of these publications leg, both identification and threshold assessed), 43 studies were ultimately appropriate for meta-analysis. Data Extract ion: Effect sizes were calculated for each study by expressing differe nces between patient and control group means in SD units (Cohen's d). Data Synthesis: Extremely large effect sizes were shown across all tas ks in both AD and PD groups. Both between-group analyses using the Man n-Whitney U test and within-group analyses using Friedman 2-way analys is of variance did not reveal any significant differences (all P > .30 ). Conclusions: As expected, severe deficits were found for both patie nts with AD and PD in each of the 3 olfactory domains relative to cont rols. However, no discriminating olfactory deficits were seen between patient groups or among the 3 measured olfactory domains, suggesting a similar disturbance in olfactory function between patients with AD an d PD.