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Hyperthyroidism

Medical form for ordering blood tests, stethoscope and pen

What is Hyperthyroidism

Hyperthyroidism is an imbalance of metabolism caused by overproduction of thyroid hormone. The thyroid gland is located in the neck. It produces several hormones which control the way that every cell in the body uses energy (metabolism). The thyroid is part of the endocrine system.

Statistics on Hyperthyroidism

Hyperthyroidism affects 2-5% of all women mainly between 20 and 40 years old. One study estimated the incidence to be 1-2 cases/1000 per year with women affected 10 times more often than men.

Risk Factors for Hyperthyroidism

  • Graves’ disease – most common cause (due to IgG antibodies binding to the TSH receptor and stimulating thyroid hormone production).
  • Toxic multinodular goitre: many patients are euthyroid for years before development of thyrotoxicosis. Occurs in older women, drug therapy rarely successful in inducing a prolonged remission
  • Toxic adenoma
  • Thyroiditis (De Quervain’s Thyroiditis, factitia – surreptitious T4 consumption), drugs (amiodarone), metastatic differentiated thyroid carcinoma and TSH-secretion tumours (e.g. of pituitary).
  • Thyroid crisis precipitated by infection, stress, surgery or radioactive iodine therapy in an unprepared patient.

Progression of Hyperthyroidism

With the exception of Graves’ disease and subacute thyroiditis, none of the known causes are associated with spontaneous remission. Thus therapeutic intervention is necessary to alter the natural history of the disease.

The severity of complications varies with the duration of the hyperthyroidism and presence of underlying disease. Older patients tolerate hyperthyroidism less well than younger patients, especially the cardiac manifestations.

How is Hyperthyroidism Diagnosed?

  • Full blood count – may see a mild normocytic normochromic anameia and a mild granulocytopaenia with relative lymphocytosis.
  • Urea and Electrolytes
  • Calcium and Phosphate – may see elevated calcium
  • ALP – may be elevated.
  • Lipids – may see hypocholesterolaemia

Prognosis of Hyperthyroidism

Hyperthyroidism caused by Graves’ disease is usually progressive and has many associated complications, some of which are severe and affect quality of life. These include complications caused by use of radioactive iodine, surgery, and medications to replace thyroid hormones. However, hyperthyroidism is generally treatable and rarely fatal.

How is Hyperthyroidism Treated?

Anti-thyroid drugs

  • Carbimazole – blocks thyroid hormone sythesis and some immunosuppressive effects. May take 10-20 days to see clinical benefits. May use Beta blockers to provide rapid symptomatic control.
  • Reduce carbimazole over 12-18 months.
  • Another option is to use full doses of carbimazole while replacing thyroid activity with thyroxine.
  • If develop sore throat or unexplained fever must seek urgent blood count (agranulocytosis is the most serious side effect of carbimazole).

Radioactive Iodine

  • accumulates in gland and destroys it by local irradiation.
  • Indications are a recurrence after drug treatment, poor compliance or side effects with carbimazole.
  • More commonly used in older patients.
  • Effective in 75% in 4-12 weeks.

Surgery

  • subtotal thyroidectomy – only in patients that have been rendered euthyorid (normal thyroid hormone levels). Antithyroid drugs stopped 10-14 days before operation and replaced with potassium iodide (inhibits thyroid hormone release and reduces the vasuclarity of the gland).
  • Indications for surgery – large goitres, recurrence after drug treatment, poor compliance or side effects with carbimazole.

Management of thyroid crisis

Take blood for full blood count, glucose, urea and electrolytes and thyroxine. Large doses of carbimazole and propanolol, iodine to blockacutely the release of theyroid hormone from the gland and dexamehtasone which inhibits peripheral conversion of T4 to T3. Supportive treatment (oxygenm fluids and management of hyperpyrexia).

Hyperthyroidism References

  1. Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001
  2. Cotran, Kumar, Collins 6th edition. Robbins Pathologic Basis of Disease. WB Saunders Company. 1999.
  3. Hurst JW (Editor-in-chief). Medicine for the practicing physician. 4th edition Appleton and Lange 1996.
  4. Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002 Pg 427-430.
  5. Longmore M, Wilkinson I, Torok E. OXFORD HANDBOOK OF CLINICAL MEDICINE. Oxford Universtiy Press. 2001
  6. MEDLINE Plus

Dates

Posted On: 7 September, 2003
Modified On: 30 September, 2015

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