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SOURCE

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Source: Jonklaas J, Kane MP. Thyroid disorders. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146066204. Accessed April 14, 2017.

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CONDITION/DISORDER SYNONYMS

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  • Thyrotoxicosis.

  • Overactive thyroid.

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DEFINITION

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  • Clinical and biochemical syndrome resulting from increased thyroid hormone production.

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ETIOLOGY

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  • TSH-secreting pituitary adenomas.

  • Graves’ disease.

  • Trophoblastic diseases.

  • Thyroid autonomy.

  • Toxic adenoma.

  • Multinodular goiter.

  • Subacute thyroiditis.

  • Painless thyroiditis.

  • Ectopic thyroid tissue.

  • Struma ovarii.

  • Exogenous thyroid hormone sources.

  • Medications.

  • Foods.

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PATHOPHYSIOLOGY

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  • Thyrotoxicosis results when tissues exposed to excessive levels of thyroxine (T4), triiodothyronine (T3), or both.

  • TSH-secreting pituitary tumors release active hormone unresponsive to normal feedback control.

  • In Graves’ disease, hyperthyroidism results from action of thyroid-stimulating antibodies (TSAb).

  • Autonomous thyroid nodule (toxic adenoma) is thyroid mass whose function is independent of pituitary control.

  • In multinodular goiters, follicles with autonomous function generate more thyroid hormone than required.

  • Painful subacute thyroiditis often develops after viral illness.

  • Painless thyroiditis may have underlying autoimmune cause.

  • Amiodarone may induce thyrotoxicosis and may also cause destructive thyroiditis with loss of thyroglobulin and thyroid hormones.

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EPIDEMIOLOGY

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  • In National Health and Nutrition Examination Survey III:

    • 0.7% of those surveyed had subclinical hyperthyroidism and 0.5% had clinically significant hyperthyroidism.

    • Prevalence of suppressed TSH peaked for people aged 20–39, declined in those 40–79, and increased again in those 80 or older.

    • Abnormal TSH levels were more common among women than men.

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CLINICAL PRESENTATION

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SIGNS AND SYMPTOMS
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  • Symptoms:

    • Nervousness.

    • Anxiety.

    • Palpitations.

    • Emotional lability.

    • Easy fatigability.

    • Heat intolerance.

    • Weight loss with increased appetite.

    • Increased frequency of bowel movements.

    • Proximal muscle weakness.

    • Scanty or irregular menses in women.

  • Signs:

    • Thyroid enlargement.

    • Exophthalmos.

    • Pretibial myxedema.

    • Warm, smooth, moist skin and unusually fine hair.

    • Onycholysis.

    • Lid lag.

    • Resting tachycardia, widened pulse pressure, and systolic ejection murmur.

    • Gynecomastia in men.

    • Fine tremor of protruded tongue and outstretched hands.

    • Hyperactive deep tendon reflexes.

  • Thyroid storm:

    • Decompensated thyrotoxicosis.

    • High fever (often above 39.4°C [103°F])

    • Tachycardia.

    • Tachypnea.

    • Dehydration.

    • Delirium.

    • Coma.

    • Nausea.

    • Vomiting.

    • Diarrhea.

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DIAGNOSIS

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LABORATORY TESTS
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  • TSH, total T4, free T4, T3 resin uptake, free thyroxine index, 24-hour radioactive iodine uptake (RAIU).

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IMAGING
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  • Thyroid scan shows areas of autonomously functioning thyroid tissue in multinodular goiters.

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DIFFERENTIAL DIAGNOSIS
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DESIRED OUTCOMES

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  • Eliminate excess thyroid hormone.

  • Minimize symptoms and long-term consequences.

  • Provide individualized therapy based on:

    • Disease type and severity.

    • Patient age and sex.

    • Existence of nonthyroid conditions.

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