A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
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Abbreviations & Definitions

Pituitary-thyroid feed-back regulation. The pituitary gland behaves like a thermostat and the thyroid gland acts as a furnace while thyroid hormones play a role much like ambient heat.

TSH (thyrotropin) is pituitary Thyroid Stimulating Hormone, which stimulates the thyroid gland to release thyroid hormone.

Hypothyroidism occurs when the thyroid fails to make sufficient thyroid hormone and the patient develops gradations of hypothyroidism from overt to subclinical.

Thyroxine (T4) is the main form of thyroid hormone made by the thyroid gland but much of it is converted in the body to Triiodothyronine Triiodothyronine (T3) is the most potent form of thyroid hormone.

Hyperthyroidism = overactive thyroid gland.

Thyrotoxicosis A syndrome caused by an excess of thyroid hormone.

Subclinical hyperthyroidism An asymptomatic condition with a low TSH and normal thyroid hormone levels.

Euthyroid = is normal thyroid function

SF-336 A multipurpose health survey of health and

POMS The Profile of Mood States (below for links to SF-36 and POMS)

What is the study about? Health status, mood and cognition in experimentally induced subclinical thyrotoxicosis.

The full article title: “Health status, mood and cognition in experimentally-induced subclinical thyrotoxicosis.” It is in the May 2008 Issue of the Journal of Clinical Endocrinology and Metabolism (volume 93 Issue 5, pages 1730-36). The authors are MH Samuels, KG Schuff, NE Carlson, P Carello, and JS Janowsky.The abstract can be obtained:

What is known about the problem being studied? The authors recently found that subclinical hypothyroidism leads to decrements in health status, mood, and working memory.

What was the aim of the study? The aim of this double-blind, randomized, crossover study was to establish whether subclinical thyrotoxicosis also alters health status, mood, and cognitive function.

Who was studied? In all, 33 adult volunteers with hypothyroidism were studied.

How was the study done? Subjects were randomly assigned to receive either their usual doses of levothyroxine (L-T4) (euthyroid arm) or higher doses of L-T4 aimed at achieving a low serum TSH mU/L (subclinical thyrotoxicosis arm). Subjects were then tested with SF-36 and POMS (See Box) and Hyperthyroid Symptom Scale for symptoms of thyrotoxicosis. A battery of tests for different forms of memory was administered to assess different cognition areas of the brain.

What were the results of the study? Study subjects were unable to reliably predict which arm was the subclinical thyrotoxicosis arm. The study found a slight impairment of self-perceived physical health status but found improvements in mental health and mood in subclinically thyrotoxic volunteers. Motor learning was also improved.

What are the Limitations of this study? This study model circumvents the limitations in studying endogenous subclinical hyperthyroidism, such as subject recruitment and subjects’ awareness of their thyroid status. It also circumvents limitations in studying patients receiving suppressive L-T4 doses for nodular thyroid disease or thyroid cancer,

What are the implications of this study? Patients with subclinical thyrotoxicosis experience significant improvements in mood and motor learning but have minor declines in self-perceived general and physical health status. The two studies suggest that different parts of the brain are affected with subclinical hyperthyroidism and hypothyroidism.

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