Hypothyroidism and Myxedema Coma
- Author: Erik D Schraga, MD; Chief Editor: Romesh Khardori, MD, PhD, FACP more...
Hypothyroidism is a clinical syndrome in which the deficiency or absence of thyroid hormone slows bodily metabolic processes. Symptoms can manifest in all organ systems and range in severity based on the degree of hormone deficiency. The disease typically progresses over months to years but can occur quickly following cessation of thyroid replacement medication or surgical removal of the thyroid gland.
The term myxedema refers to the thickened, nonpitting edematous changes to the soft tissues of patients in a markedly hypothyroid state. Myxedema coma, a rare, life-threatening condition, occurs late in the progression of hypothyroidism. The condition is seen typically in elderly women and is often precipitated by infection, medication, environmental exposure, or other metabolic-related stresses. Because rapid confirmatory laboratory tests are often unavailable, the diagnosis may be made on clinical grounds with treatment started promptly.
For more information, see Medscape's Hypothyroidism Resource Center.
Thyroid hormone is secreted in response to stimulation of the thyroid gland by thyroid-stimulating hormone (TSH) from the anterior pituitary gland. TSH is released through the action of thyrotropin-releasing hormone (TRH) from the hypothalamus.
Hypothyroidism can be caused by permanent loss or atrophy of functional thyroid tissue (primary hypothyroidism), insufficient stimulation of a normal thyroid gland by as a result of hypothalamic or pituitary disease (secondary hypothyroidism, often accompanied by compensatory thyroid gland enlargement), or a defect in the TSH molecule (control hypothyroidism).
Primary hypothyroidism accounts for approximately 90-95% of hypothyroidism, with a predominantly autoimmune-mediated etiology. TSH hypersecretion produces excessive thyroid tissue, resulting in goiter formation. Surgical and radiation ablation account for a large percentage of acquired cases of hypothyroidism. Congenital abnormalities, malignancies, and infiltrative disorders including amyloidosis and sarcoidosis can also lead to the disease. Iodine deficiency is rarely responsible for hypothyroidism in developed countries; however, it remains the primary cause worldwide.
Suprathyroidal disorders including hypopituitarism and hypothalamic lesions account for fewer than 10% of cases. Rarely, peripheral resistance to thyroid hormone may occur.
The congenital absence or deficiency of thyroid tissue may result in cretinism, a neurodevelopmental disorder characterized by lethargy, poor peripheral circulation, constipation, and goiter. Because infants are asymptomatic, neonatal screening is vital to prevent permanent sequelae.
Reports on screening surveys for thyroid disease show an incidence of 5.8% for subclinical thyroid abnormalities. However, those with overt signs and symptoms of hypothyroidism likely comprise less than 2% of women and 0.2% of men.
Myxedema coma occurs rarely, appearing in 0.1% of all cases of hypothyroidism.
In developed countries, the incidence of subclinical hypothyroidism is approximately 8% in women and 3% in men. Endemic goiter usually occurs in environmentally iodine-deficient areas; throughout the world, goiter is estimated to affect 200 million people. Goiter is most common in mountainous areas of the Alps, Himalayas, and Andes, possibly due to low soil iodine content as a result of leaching away of minerals as glaciers melt.
Anecdotal reports indicate the disease appears more often in white and Hispanic populations.
Incidence is greater in females than males (female-to-male ratio 5-10:1).
The incidence of primary hypothyroidism increases progressively with age, typically at 40-50 years. After age 60 years, the prevalence of hypothyroidism may be as high as 8-10% in women.
Dubbs SB, Spangler R. Hypothyroidism: causes, killers, and life-saving treatments. Emerg Med Clin North Am. 2014 May. 32 (2):303-17. [Medline].
[Guideline] Screening for congenital hypothyroidism: US Preventive Services Task Force reaffirmation recommendation. Ann Fam Med. 2008 Mar-Apr. 6(2):166. [Medline].
Teng W, Shan Z, Teng X, Guan H, et. al. Effect of iodine intake on thyroid diseases in China. N Eng J Med. Jun 2006. 354(26):2783-2793. [Medline].
Popoveniuc G, Chandra T, Sud A, Sharma M, Blackman MR, Burman KD, et al. A diagnostic scoring system for myxedema coma. Endocr Pract. 2014 Aug. 20 (8):808-17. [Medline].
Lee CH, Wira CR. Severe angioedema in myxedema coma: a difficult airway in a rare endocrine emergency. Am J Emerg Med. 2009 Oct. 27(8):1021.e1-2. [Medline].
Sanda S, Newfield RS. A child with pericardial effusion and cardiac tamponade due to previously unrecognized hypothyroidism. J Natl Med Assoc. Dec 2007. 99(12):1411-3. [Medline].
Ragland G. Hypothyroidism and myxedema coma. Tintinalli JE, Krome RL, et al, eds. Emergency Medicine: A Comprehensive Study Guide. 4th ed. New York, NY: McGraw-Hill; 1996. 964-67.
Unuane D, Tournaye H, Velkeniers B, Poppe K. Endocrine disorders & female infertility. Best Pract Res Clin Endocrinol Metab. 2011 Dec. 25(6):861-73. [Medline].
Flynn RW, MacDonald TM, Morris AD. The thyroid epidemiology, audit, and research study: thyroid dysfunction in the general population. J Clin Endocrinol Metab. 2004 Aug. 89(8):3879-84. [Medline].
Franklyn JA. The management of hyperthyroidism. N Engl J Med. 1994 Jun 16. 330(24):1731-8. [Medline].
Hehrmann R. [Coma in myxedema--a rare complication of hypothyroidism. Possible iatrogenic factors should be taken into account]. Fortschr Med. 1996 Dec 10. 114(34):474-8. [Medline].
Kinuya S, Michigishi T, Tonami N, et al. Reversible cerebral hypoperfusion observed with Tc-99m HMPAO SPECT in reversible dementia caused by hypothyroidism. Clin Nucl Med. 1999 Sep. 24(9):666-8. [Medline].
Menendez CE, Rivlin RS. Thyrotoxic crisis and myxedema coma. Med Clin North Am. 1973 Nov. (6):1463-70. [Medline].
Rimar D, Kruzel-Davila E, Dori G, Baron E, Bitterman H. Hyperammonemic coma--barking up the wrong tree. J Gen Intern Med. Apr 2007. 22(4):549-52. [Medline].
Roberts CG, Ladenson PW. Hypothyroidism. Lancet. 2004 Mar 6. 363(9411):793-803. [Medline].
Smith SA. Commonly asked questions about thyroid function. Mayo Clin Proc. 1995 Jun. 70(6):573-7. [Medline].