Relationship Between Thyroid Hormone Levels and Regional Cerebral Blood Flow in Alzheimer Disease

Abstract

Subclinical thyroid disease and even variations in thyroid function within the normal range is associated with cognitive function and a risk of Alzheimer disease (AD). Several studies reported the effect of thyroid hormones on cerebral blood flow. The aim of this study was to objectively evaluate regional cerebral blood flow (rCBF) in association with thyroid hormone levels within the normal range in patients with AD. Serum thyroid-stimulating hormone (TSH), free T3, and free T4 levels were measured in 62 patients with AD (23 men and 39 women; age 56 to 91 y; mean age 77.3 y) and 27 control subjects (9 men and 18 women; age 61 to 93 y; mean age 75.8 y). The 99mTc ethylcysteinate dimer single photon emission computed tomography was performed in all subjects. The rCBF in the region of interest was measured by the noninvasive Patlak plot method and calculated using FineSRT, which is a fully automated region of interest technique. No significant correlation was found between thyroid hormone levels and Mini-Mental State Examination scores or global CBF values. Serum levels of TSH, but not free T3 or free T4, were significantly inversely correlated with rCBF in the middle and inferior temporal regions of right cerebral hemisphere in patients with AD. Control subjects showed no significant correlation between thyroid hormone levels and rCBF. Although these findings of a regional relationship must be considers preliminary, this study proposed the hypothesis that altered TSH levels within the normal range may be related to brain perfusion in right temporal region.

Evaluation of Regional Cerebral Blood Flow in Alzheimer's Disease Patients with Subclinical Hypothyroidism

“…Similarly, our AD patients with SCH did not show any decreased rCBF in the mesial temporal lobe. Moreover, the results of the present study are supported by our previous findings that serum TSH levels are inversely correlated with rCBF in the temporal lobe in AD patients [10]. …”

“…The Mini-Mental State Examination (MMSE) was used to evaluate cognitive function. Routine laboratory tests, including TSH, free triiodothyronine (fT 3 ), and free thyroxine (fT 4 ) levels, were performed according to previous studies (normal ranges: TSH, 0.35-4.94 µIU/ml; fT 3 , 1.7-3.71 pg/ml; fT 4 , 0.7-1.48 ng/dl) [10]. SCH was defined as normal levels of fT 3 and fT 4 in the presence of a high TSH level [4].…”

Functional correlates of TSH, fT3 and fT4 in Alzheimer disease: a F-18 FDG PET/CT study

“…found that serum levels of TSH, but not free T3 or free T4, were significantly inversely correlated with regional cerebral blood flow (rCBF) in the middle and inferior temporal regions of right cerebral hemisphere in patients with AD. Control subjects showed no significant correlation between thyroid hormone levels and rCBF 46 . The differences in the results from Kimura N. et al .…”

Subclinical Hypothyroidism and Cognitive Dysfunction in the Elderly

“…In order to explain why the correlation at multiple regression analysis between subclinical hypothyroidism and cognitive status, as explored by MMSE, is lost when examining single aspects such as long-term memory (PMT) and selective attention (MT), we can hypothesize a different degree of sensitivity for the specific brain areas playing diverse functions to hormonal and metabolic changes as well as alterations in perfusion [42,43]. There is, in fact, evidence, using SPECT, that cerebral hypoperfusion may have effects on areas controlling attention, motor speed, memory and visual-spatial processes in overt hypothyroidism [42], even if the mechanisms by which thyroid failure can affect the regional cerebral perfusion have not yet been elucidated.…”