FreeSurfer-based amygdala subfield volumetry in long COVID and ME/CFS: clinical and immunological correlations

Abstract

Background Long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) share debilitating symptoms and have been associated with limbic-system dysfunction. We investigated amygdala subfield volumes to identify disease-specific neuroanatomical features and their clinical and immunological correlates. Methods We prospectively examined 27 patients with long COVID, 38 patients with ME/CFS, and 47 healthy controls (HCs). Amygdala subfields were segmented using high-resolution 3-T MRI and FreeSurfer software. Group comparisons were performed using analysis of covariance, and partial correlations with clinical and immunological indices, including autoantibodies, plasmablasts, regulatory T cells (Tregs), and Eomesodermin-positive helper T cells (Eomes+ Th cells), were assessed. Results Patients with long COVID had nominally larger right cortical nucleus volumes than HCs (raw p = 0.040; Bonferroni-adjusted p = 0.119), whereas patients with ME/CFS had a nominally larger left paralaminar nucleus (raw p = 0.048; Bonferroni-adjusted p = 0.145). In long COVID, G-protein-coupled receptor (GPCR) autoantibodies were nominally negatively associated with right medial nucleus volume. In ME/CFS, performance status was nominally positively associated with the right basal nucleus, right paralaminar nucleus, and right whole amygdala, and plasmablasts were nominally positively associated with the right corticoamygdaloid transition area. No group difference or partial correlation remained significant after correction for multiple testing. Conclusion Although no finding survived correction for multiple testing, the exploratory results suggest that amygdala-related structural variation may be relevant to both long COVID and ME/CFS. The nominal, uncorrected within-group patterns centered on olfactory-related amygdala nuclei and GPCR autoantibodies in long COVID, and on amygdala structure, functional severity, and plasmablasts in ME/CFS; however, these patterns do not support a conclusion of between-group differences. These observations are hypothesis-generating and do not establish disease-specific mechanisms. Prespecified validation in larger longitudinal and independent cohorts is required.