Reduced cerebrospinal fluid level of thyroxine in patients with Alzheimer's disease

Background: Little is known of the association between thyroid hormones in the central nervous system and Alzheimer's disease (AD). We determined thyroid hormone levels in serum and cerebrospinal fluid (CSF) in a well-defined homogeneous mono-center population. Methods: Fifty-nine consecutive patients under primary evaluation for cognitive impairment were recruited. The participants included patients with AD or mild cognitive impairment (MCI) diagnosed with AD upon follow-up (n = 31), patients with stable MCI (SMCI, n = 13), patients with other dementias (n = 15), and healthy controls (n = 19). Thyroid hormones in serum and CSF and AD biomarkers in CSF were analyzed using established immunochemical assays. Cognitive impairment was estimated using mini-mental state examination (MMSE). Results: Serum levels of free and total thyroxine (T4) and triiodothyronine (T3) were similar in all groups whereas a marginal increase in serum thyroid-stimulating hormone (TSH) level was observed in the AD patients. The CSF level of total T4 was decreased in patients with AD and other dementias compared to SMCI (both P = 0.01) and healthy controls (both P = 0.001), whereas CSF levels of TSH and total T3 were unchanged. In the total study population, CSF total 14 level correlated positively with MMSE score (r = 0.26, P < 0.05) and negatively with CSF total-tau (T-Tau) level (r = -0.23, P < 0.05). Conclusion: Patients with AD as well as other dementias had signs of mild brain hypothyroidism, which could only to a small extent be detected in serum values. (C) 2012 Elsevier Ltd. All rights reserved