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Journal of Clinical Endocrinology & Metabolism , doi:10.1210/jc.2007-1957
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The Journal of Clinical Endocrinology & Metabolism Vol. 93, No. 5 1730-1736
Copyright © 2008 by The Endocrine Society

Health Status, Mood, and Cognition in Experimentally Induced Subclinical Thyrotoxicosis

M. H. Samuels, K. G. Schuff, N. E. Carlson, P. Carello and J. S. Janowsky

Division of Endocrinology, Diabetes and Clinical Nutrition (M.H.S., K.G.S.), Division of Biostatistics (N.E.C.), and Department of Behavioral Neurosciences (P.C., J.S.J.), Oregon Health & Science University, Portland, Oregon 97239

Address all correspondence and requests for reprints to: Mary H. Samuels, M.D., CR107, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239. E-mail: samuelsm{at}ohsu.edu.

Objective: Our objective was to determine whether subclinical thyrotoxicosis alters health status, mood, and/or cognitive function.

Design: This was a double-blinded, randomized, cross-over study of usual dose L-T4 (euthyroid arm) vs. higher dose L-T4 (subclinical thyrotoxicosis arm) in hypothyroid subjects.

Patients: A total of 33 hypothyroid subjects receiving L-T4 were included in the study.

Measurements: Subjects underwent measurements of health status, mood, and cognition: Short Form 36 (SF-36); Profile of Mood States (POMS); and tests of declarative memory (Paragraph Recall, Complex Figure), working memory (N-Back, Subject Ordered Pointing, and Digit Span Backwards), and motor learning (Pursuit Rotor). These were repeated after 12 wk on each of the study arms.


Figure 1
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  		FIG. 1. Study flow diagram.

 
Results: Mean TSH levels decreased from 2.15 to 0.17 mU/liter on the subclinical thyrotoxicosis arm (P < 0.0001), with normal mean free T4 and free T3 levels. The SF-36 physical component summary and general health subscale were slightly worse during the subclinical thyrotoxicosis arm, whereas the mental health subscale was marginally improved. The POMS confusion, depression, and tension subscales were improved during the subclinical thyrotoxicosis arm. Motor learning was better during the subclinical thyrotoxicosis arm, whereas declarative and working memory measures did not change. This improvement was related to changes in the SF-36 physical component summary and POMS tension subscales and free T3 levels.

Conclusions: We found slightly impaired physical health status but improvements in measures of mental health and mood in L-T4 treated hypothyroid subjects when subclinical thyrotoxicosis was induced in a blinded, randomized fashion. Motor learning was also improved. These findings suggest that thyroid hormone directly affects brain areas responsible for affect and motor function.




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