Amygdala subregion MRI alterations in Parkinson's disease correlate with olfactory function

Olfactory dysfunction affects 80-90% of Parkinson's disease (PD) patients. The amygdala, a key olfactory node, comprises functionally distinct subregions. We investigated volumetric changes in nine amygdala subregions across PD stages and their relationship with olfactory function.

In this cross-sectional study, 65 PD patients (40 early stage, Hoehn-Yahr 1.0-2.5; 25 late- stage, 3.0-5.0) and 45 healthy controls underwent high-resolution 3D-T1WI MRI. Automated segmentation quantified bilateral volumes of nine amygdala subregions. Olfactory function was assessed using Sniffin' Sticks (threshold, discrimination, identification, TDI score). Cognitive function was evaluated by MMSE. Statistical analyses included ANCOVA/GLM with Bonferroni correction and Spearman partial correlation.

PD patients exhibited significant volume reductions in bilateral cortical nucleus (Co), accessory basal nucleus (AB), cortico-amygdaloid transition area (CAT), and right anterior amygdaloid area (AAA) versus controls (P < 0.05). Bilateral Co and right AAA were already reduced in early stage PD. Controlling for age, sex, education, and intracranial volume, amygdala subregion volumes showed no statistically significant correlations with olfactory scores, though right AAA volume weakly correlated with threshold (R = 0.27) and TDI total score (R = 0.24) (P > 0.05). Additionally, the volume of the left medial subdivision (Me) of the amygdala showed a significant positive correlation with MMSE scores (R = 0.29, P = 0.026).

PD involves subregion-selective amygdala atrophy, with Co and AAA affected early, followed by AB and CAT, exhibiting a right-lateralized pattern. The weak correlation between right AAA volume and olfactory function suggests a specific role in PD-related olfactory dysfunction, providing novel insights into its structural basis. Additionally, left Me volume correlated with MMSE independent of stage, implying a structural biomarker for cognition.