Effect of olfactory bulb pathology on olfactory function in normal aging

Decline of olfactory function is frequently observed in aging and is an early symptom of neurodegenerative diseases. As the olfactory bulb (OB) is one of the first regions involved by pathology and may represent an early disease stage, we specifically aimed to evaluate the contribution of OB pathology to olfactory decline in cognitively normal aged individuals without parkinsonism or dementia. This clinicopathological study correlates OB tau, amyloid beta (A beta) and alpha-synuclein (alpha Syn) pathology densities and whole brain pathology load to olfactory identification function as measured with the University of Pennsylvania Smell Identification Test (UPSIT) and clinical data measured proximate to death in a large autopsy study including 138 cases considered non-demented controls during life. Tau pathology was frequently observed in the OB (95% of cases), while both A beta (27% of cases) and alpha Syn (20% of cases) OB pathologies were less commonly observed. A weak correlation was only observed between OB tau and olfactory performance, but when controlled for age, neither OB tau, A beta or alpha Syn significantly predict olfactory performance. Moreover, whole brain tau and alpha Syn pathology loads predicted olfactory performance; however, only alpha Syn pathology loads survived age correction. In conclusion, OB tau pathology is frequently observed in normally aging individuals and increases with age but does not appear to independently contribute to age-related olfactory impairment suggesting that further involvement of the brain seems necessary to contribute to age-related olfactory decline.

Automated summary

The decline of olfactory function is frequently observed in aging. This study found that tau pathology is commonly observed in the olfactory bulb of normally aging individuals, but it does not independently contribute to age-related olfactory decline. Further involvement of the brain seems to be necessary for age-related olfactory impairment.