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KEY POINTS

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  • For patients with hypo- or hyperthyroidism, MTM providers should review the medication list for drugs that may be contributing to thyroid dysfunction.

  • MTM providers should be aware of and inquire about symptoms that may indicate under- or overtreatment of a thyroid condition. A thyroid function panel must confirm clinical suspicion.

  • MTM providers should assess for conditions (eg, interacting medications or nonadherence) that may alter dosage requirements of thyroid medications.

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INTRODUCTION TO THYROID DISORDERS

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The thyroid normally synthesizes 2 thyroid hormones, thyroxine (T4) and triiodothyronine (T3), after glandular stimulation by thyroid-stimulating hormone (TSH).1 Prior to this, thyrotropin-releasing hormone (TRH) produced by the hypothalamus stimulates the anterior pituitary to release TSH. This hypothalamic-pituitary-thyroid axis maintains thyroid hormone homeostasis through a negative feedback loop. That is, adequate thyroid hormone levels inhibit the release of TRH and TSH from the hypothalamus and pituitary, respectively (Figure 36-1).

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Figure 36-1.

Hypothalamic-Pituitary-Thyroid Hormone Axis

Source: Reproduced with permission from Greenspan FS: The thyroid gland. In: Greenspan FS, Gardner D. eds. Basic and Clinical Endocrinology. 6th ed. New York, NY: McGraw-Hill, 2001, p 217.

In both the hypothalamus and pituitary, 3,5',3-triiodothyronine (T3) is primarily responsible for inhibition of thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH) secretion. T4 = thyroxine.

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Thyroid hormones regulate metabolism and affect essentially every organ system in the human body. T4 is produced in greater amounts than T3, but T4 exhibits less biological activity. Production of T3 occurs primarily through peripheral conversion of T4 by deiodinase enzymes (80%), with approximately 20% of T3 produced directly by the thyroid gland.1

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Hyperthyroidism

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Hyperthyroidism is a condition in which there is inappropriate synthesis and secretion of thyroid hormone (either T3, T4, or both) from the thyroid gland2,3. Thyroid hormone excess results either from overproduction (eg, Graves disease, toxic multinodular goiter, toxic adenoma) or, infrequently, thyroid inflammation (eg, thyroiditis). Graves disease, an autoimmune disorder, accounts for 60% to 80% of cases of hyperthyroidism.

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Other Terms Associated with Hyperthyroidism

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  • Thyrotoxicosis—a clinical state marked by inappropriately high thyroid hormone action in the peripheral tissues

    • Hyperthyroidism may cause thyrotoxicosis, but the terms are not synonymous.

  • Thyroid storm—a sudden and life-threatening condition with an increase in thyrotoxicosis signs and symptoms, including fever greater than 102°F, tachycardia, tachypnea, nausea, vomiting, diarrhea, abdominal pain, and psychosis

    • Usually precipitated by trauma, surgery, or infection

    • Arrhythmias, heart failure, ischemic heart disease, or coma may develop

    • Requires prompt treatment and hospitalization

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Hypothyroidism

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Hypothyroidism indicates a failure of the thyroid gland to produce or secrete adequate thyroid hormone to match the ...

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