Biomarkers

Area of Science:

• Neuroimaging
• Neuropathology
• Olfactory System

Background:

• The piriform cortex, an olfactory region, may show early Alzheimer's (AD) and Parkinson's disease (PD) pathology.
• Amyloid-tau overlap is prominent in the medial temporal lobe, but its association within the piriform cortex is not well understood.

Purpose of the Study:

• To quantify simultaneous amyloid and tau uptake in the piriform cortex and other medial temporal structures.
• To compare these pathologies across AD, mild cognitive impairment (MCI), healthy controls (HC), and PD cohorts.

Main Methods:

• Dual PET-MR imaging was used with amyloid (¹⁸F-Florbetaben) and tau (¹⁸F-PI-2620) tracers.
• Automated and manual segmentation of the piriform cortex, entorhinal-perirhinal cortices, amygdala, and hippocampus was performed.
• Cross-sectional data from 47 participants (AD, MCI, HC, PD) were analyzed.

Main Results:

• Global and regional amyloid uptake (piriform cortex, entorhinal-perirhinal, amygdala) increased with disease severity, but not in the hippocampus.
• Amyloid burden was higher in amyloid-positive HC compared to amyloid-negative HC in these regions.
• Amyloid positively correlated with tau uptake in the entorhinal-perirhinal cortex, piriform cortex, and amygdala, but not the hippocampus.

Conclusions:

• Early increases in amyloid-PET are observed in the primary olfactory cortex (piriform cortex).
• Amyloid accumulation in the piriform cortex strongly correlates with tau uptake, similar to the entorhinal cortex and amygdala.
• These findings highlight the piriform cortex's distinct pathological profile compared to the hippocampus in neurodegenerative diseases.