Does olfactory dysfunction have the same relationship with limbic system integrity in Alzheimer’s and Parkinson’s disease?

Abstract

AbstractBackgroundWe have demonstrated that olfactory dysfunction is common in Alzheimer’s disease (AD), and is associated with poorer episodic memory performance and medial temporal lobe (MTL) integrity in groups at risk for AD. Olfactory decline is also common in Parkinson’s disease (PD); however, the difference in pathology between these diseases remains poorly understood.MethodUsing data from the Comprehensive Assessment of Neurodegeneration in Aging (COMPASS‐ND) study, we compared older adults with subjective cognitive decline (SCD; N=55, Mage =70.1, %female=78), mild cognitive impairment (MCI; N=100, Mage =71.2, %female=45) and AD (N=47, Mage =74.8, %female=31) with those at risk for (PD‐MCI; N=25, Mage =71.4, %female=20) and with Parkinson’s disease (PD; N=34, Mage =66.5, %female=44) on measures of olfaction (Brief Smell Identification Test), cognition (episodic, working and semantic memory), and structural MRI (volume and cortical thickness of the MTL and orbitofrontal cortex). All analyses controlled for age, sex, and education; MRI analyses also controlled for total intracranial volume.ResultOur analyses revealed that olfactory function was highest in SCD (M=10.33, SD=1.69), and declined in MCI (M=8.84, SD=2.98), and AD groups (M=6.06, SD=2.73) successively. The PD group (M=7.12, SD=2.78) did not differ from PD‐MCI group (M=5.28, SD=3.26), and was in line with the poor performance of the AD participants. These groups had poorer olfactory performance compared to the SCD and MCI groups.ConclusionOlfactory deficits are present in PD participants regardless of MCI. We will also report on whether olfactory function predicts MTL integrity in PD, as it does in individuals at risk for AD.