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Hypothyroidism

Not to be confused with Hyperthyroidism.

Hypothyroidism
Other namesUnderactive thyroid, low thyroid, hypothyreosis
Molecular structure of the thyroxine molecule
Molecular structure of thyroxine, which is deficient in hypothyroidism
Pronunciation
SpecialtyEndocrinology
Symptomsextreme fatigue, poor ability to tolerate cold, feeling tired, muscle aches, constipation, weight gain,[3] depression, anxiety, irritability[4]
ComplicationsDuring pregnancy can result in cretinism in the baby[5]
Usual onset> 60 years old[3]
CausesIodine deficiency, Hashimoto's thyroiditis[3]
Diagnostic methodBlood tests (thyroid-stimulating hormone, thyroxine)[3]
Differential diagnosisDepression, dementia, heart failure, chronic fatigue syndrome[6]
PreventionSalt iodization[7]
TreatmentLevothyroxine[3]
Frequency5% (USA)[8]

Hypothyroidism (also called underactive thyroid, low thyroid or hypothyreosis) is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormones.[3] It can cause a number of symptoms, such as poor ability to tolerate cold, extreme fatigue, muscle aches, constipation, slow heart rate, depression, and weight gain.[3] Occasionally there may be swelling of the front part of the neck due to goitre.[3] Untreated cases of hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome.[5]

Worldwide, too little iodine in the diet is the most common cause of hypothyroidism.[8][9] Hashimoto's thyroiditis is the most common cause of hypothyroidism in countries with sufficient dietary iodine.[3] Less common causes include previous treatment with radioactive iodine, injury to the hypothalamus or the anterior pituitary gland, certain medications, a lack of a functioning thyroid at birth, or previous thyroid surgery.[3][10] The diagnosis of hypothyroidism, when suspected, can be confirmed with blood tests measuring thyroid-stimulating hormone (TSH) and thyroxine (T4) levels.[3]

Salt iodization has prevented hypothyroidism in many populations.[7] Thyroid hormone replacement with levothyroxine treats hypothyroidism.[3] Medical professionals adjust the dose according to symptoms and normalization of the thyroxine and TSH levels.[3] Thyroid medication is safe in pregnancy.[3] Although an adequate amount of dietary iodine is important, too much may worsen specific forms of hypothyroidism.[3]

Worldwide about one billion people are estimated to be iodine-deficient; however, it is unknown how often this results in hypothyroidism.[11] In the United States, hypothyroidism occurs in approximately 5% of people.[8] Subclinical hypothyroidism, a milder form of hypothyroidism characterized by normal thyroxine levels and an elevated TSH level, is thought to occur in 4.3–8.5% of people in the United States.[8] Hypothyroidism is more common in women than in men.[3] People over the age of 60 are more commonly affected.[3] Dogs are also known to develop hypothyroidism, as are cats and horses, albeit more rarely.[12] The word hypothyroidism is from Greek hypo- 'reduced', thyreos 'shield', and eidos 'form', where the two latter parts refer to the thyroid gland.[13]

  1. ^ "hypothyroidism". Dictionary.com Unabridged (Online). n.d.
  2. ^ "hypothyroidism - definition of hypothyroidism in English from the Oxford dictionary". OxfordDictionaries.com. Archived from the original on March 11, 2013. Retrieved 2016-01-20.
  3. ^ a b c d e f g h i j k l m n o p q "Hypothyroidism". National Institute of Diabetes and Digestive and Kidney Diseases. March 2013. Archived from the original on 5 March 2016. Retrieved 5 March 2016.
  4. ^ "Psychological symptoms and thyroid disorders". British Thyroid Foundation. 11 September 2019.
  5. ^ a b Preedy V (2009). Comprehensive Handbook of Iodine Nutritional, Biochemical, Pathological and Therapeutic Aspects. Burlington: Elsevier. p. 616. ISBN 9780080920863.
  6. ^ Ferri FF (2010). Ferri's differential diagnosis : a practical guide to the differential diagnosis of symptoms, signs, and clinical disorders (2nd ed.). Philadelphia, PA: Elsevier/Mosby. p. Chapter H. ISBN 978-0323076999.
  7. ^ a b Syed S (April 2015). "Iodine and the "near" eradication of cretinism". Pediatrics. 135 (4): 594–6. doi:10.1542/peds.2014-3718. PMID 25825529. S2CID 27647943.
  8. ^ a b c d Garber JR, Cobin RH, Gharib H, Hennessey JV, Klein I, Mechanick JI, Pessah-Pollack R, Singer PA, Woeber KA (December 2012). "Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association". Thyroid. 22 (12): 1200–35. doi:10.1089/thy.2012.0205. PMID 22954017.
  9. ^ Chakera AJ, Pearce SH, Vaidya B (2012). "Treatment for primary hypothyroidism: current approaches and future possibilities". Drug Design, Development and Therapy (Review). 6: 1–11. doi:10.2147/DDDT.S12894. PMC 3267517. PMID 22291465.
  10. ^ Persani L (September 2012). "Clinical review: Central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges". The Journal of Clinical Endocrinology and Metabolism (Review). 97 (9): 3068–78. doi:10.1210/jc.2012-1616. PMID 22851492.
  11. ^ Cooper, DS, Braverman LE, eds. (2012-07-12). Werner & Ingbar's the thyroid : a fundamental and clinical text (10th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins Health. p. 552. ISBN 978-1451120639. Archived from the original on 2016-05-20.
  12. ^ "Hypothyroidism". Merck Veterinary Manual, 10th edition (online version). 2012. Archived from the original on 2012-08-23. Retrieved 2013-12-25.
  13. ^ Mosby's Medical Dictionary (9 ed.). Elsevier Health Sciences. 2013. p. 887. ISBN 9780323112581. Archived from the original on 2016-03-07.

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