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KEY CONCEPTS

KEY CONCEPTS

  • image Thyrotoxicosis is most commonly caused by Graves’ disease, which is an autoimmune disorder in which thyroid-stimulating antibody (TSAb) directed against the thyrotropin receptor elicits the same biologic response as thyroid-stimulating hormone (TSH).

  • image Hyperthyroidism may be treated with antithyroid drugs such as methimazole (MMI) or propylthiouracil (PTU), radioactive iodine (RAI: sodium iodide-131 [131I]), or surgical removal of the thyroid gland; selection of the initial treatment approach is based on patient characteristics such as age, concurrent physiology (eg, pregnancy), comorbidities (eg, chronic obstructive lung disease), and convenience.

  • image MMI and PTU reduce the synthesis of thyroid hormones and are similar in efficacy, although their dosing ranges differ by 20-fold. Overall, PTU has a greater incidence of side effects. Agranulocytosis is a rare but severe adverse effect associated with both medications.

  • image Response to MMI and PTU is seen in 4 to 6 weeks and therefore β-blocker therapy may be concurrently initiated to reduce adrenergic symptoms. Maximal response is typically seen in 4 to 6 months; treatment usually continues for 1 to 2 years, and therapy is monitored by clinical signs and symptoms and by measuring the serum concentrations of TSH and free thyroxine (FT4).

  • image Adjunctive therapy with β-blockers controls the adrenergic symptoms of thyrotoxicosis but does not correct the underlying disorder; iodine may also be used adjunctively in preparation for surgery and acutely for thyroid storm.

  • image Many patients choose to have ablative therapy with 131I rather than undergo repeated courses of MMI or PTU treatment; most patients receiving RAI eventually become hypothyroid and require thyroid hormone supplementation.

  • image Hypothyroidism is most often due to an autoimmune disorder known as Hashimoto’s thyroiditis.

  • image The drug of choice for replacement therapy in hypothyroidism is levothyroxine.

  • image Studies of combination therapy with levothyroxine and liothyronine have not shown reproducible benefits. This approach to the treatment of hypothyroidism requires further study.

  • image Monitoring of levothyroxine replacement therapy is achieved by observing clinical signs and symptoms and by measuring the serum TSH level. An elevated TSH indicates under-replacement; a suppressed TSH indicates over-replacement.

BEYOND THE BOOK

BEYOND THE BOOK

To get a basic understanding of hyperthyroidism and hypothyroidism, visit the Websites of National Institutes of Health and National Institute of Diabetes and Digestive and Kidney Diseases for a quick overview:

https://www.niddk.nih.gov/health-information/endocrine-diseases/hyperthyroidism

https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism

INTRODUCTION

Thyroid hormones affect the function of virtually every organ system. In a child, thyroid hormone is critical for normal growth and development. In an adult, the major role of thyroid hormone is to maintain metabolic stability. Substantial reservoirs of thyroid hormone in the thyroid gland and blood provide constant thyroid hormone availability. In addition, the hypothalamic-pituitary-thyroid axis is exquisitely sensitive to small changes in circulating thyroid hormone concentrations, and alterations in thyroid hormone secretion maintain peripheral free thyroid hormone levels within a narrow range. Patients seek medical attention for evaluation of symptoms due to abnormal thyroid ...

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