Thyroid function in patients with Alzheimer disease: Implications on response to anticholinesterase treatment

Increasing evidence supports an extensive interrelationship between thyroid hormones and the cholinergic system, which is selectively and early affected in Alzheimer disease (AD). The aim of the present study was to explore thyroid function in patients with AD before and after acetylcholinesterase inhibition treatment to possibly identify variances in response. Thyroid function tests were evaluated in 28 AD patients and 24 age and sex-matched controls. Nineteen of the patients were reevaluated after (4 mo) treatment with donepezil. Serum thyrotropin (TSH), triiodothyronine (T-3), thyroxine (T-4), the free fractions (fT(3), fT(4)) and thyroid autoantibodies were determined using standard methods. All subjects were clinically euthyroid. Patients presented with higher fT(4) and anti-thyroperoxidase levels, as compared with the controls. Significant reduction in T-4, fT(3), fT(4), and anti-thyroperoxidase levels were observed 4 months after treatment. Responders had higher T-4 and fT(4), than nonresponders, followed by significant reductions after treatment. The above, within the normal range alterations, may represent a direct effect on hormone release from the thyroid gland and/or increased conversion of T-4 to T-3 within the brain. Higher T-4 and fT(4) levels before treatment might predict a favorable response to donepezil treatment.