Associations of thyroid hormone serum levels with in-vivo Alzheimers disease pathologies in cognitively normal elderly individuals

Abstract

Introduction: The present study investigated the relationships between thyroid hormone serum levels or thyroid-stimulating hormone (TSH) and Alzheimers disease (AD)-specific biomarkers including cerebral amyloid beta (Aβ) burden, glucose metabolism, and brain structural changes in AD-signature brain regions in cognitively normal (CN) middle-aged and elderly individuals.

Methods: This study assessed 148 CN individuals who received comprehensive clinical and neuropsychological assessments that included 11C-Pittsburgh Compound B (PiB)-positron emission tomography (PET) scans, 18F-deoxyglucose (FDG)-PET scans, Magnetic resonance imaging (MRI) scans, and the quantification of serum triiodothyronine (T3), free T3, free thyroxine (fT4), and TSH levels.

Results: All participants were clinically euthyroid. Independent negative associations were found between serum fT4 levels and global cerebral Aβ deposition after controlling for the effects of age, gender, and the apolipoprotein E ε4 (APOEε4) genotype. Serum TSH level had significant association with CMglu in the precuneus after controlling for the effects of age, gender, and APOE ε4 genotype. No other thyroid hormones exhibited relationships with either brain Aβ burden, glucose metabolism or brain structural changes.

Conclusions: Even in a clinical euthyroid state, low serum fT4 levels appear to be associated with AD-specific brain changes.