Thyroid gland
Endocrine abnormalities
Thyroid gland - Hypothyroidism (adult) and myxedema

Author: Julie Guilmette, M.D. (see Authors page)
Editor: Anthony Chi, M.D.

Revised: 2 September 2016, last major update August 2016

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Hypothyroidism adult myxedema
Definition / General
Essential Features
Epidemiology
Sites
Pathophysiology
  • Secretion of thyroid hormones are regulated by the hypothalamic pituitary thyroid axis
  • In primary hypothyroidism, the following changes occur:
  • Myxedema : dermal mucinosis is caused by increased deposition of connective tissue components (glycosaminoglycans, hyaluronic acid and mucopolysaccharides) within the reticular dermis (Wikipedia-Myxedema)
    • Protein mucopolysaccharide complex binds water, resulting in nonpitting edema
  • Myxedema coma: patients with longstanding hypothyroidism often develop adaptive mechanisms, including chronic peripheral vasoconstriction, diastolic hypertension and diminished blood blood volume to preserve a normal body core temperature
  • Myxedema coma occurs when a precipitating event disrupts this homeostasis (Endotext [Internet] 2000-2015)
Etiology
Clinical Features
Diagnosis
  • For most outpatients with primary thyroid disease, serum thyrotropin (TSH) is the best screening test, although it may not be adequate for hospitalized patients (Thyroid 2012;22:1200)
  • Primary hypothyroidism is suspected when TSH is elevated, a goitrous thyroid is present, associated pituitary hormone deficiencies are absent and the thyrotropin releasing hormone stimulation test is normal (Indian J Endocrinol Metab 2011;15:S99)
  • Secondary / tertiary hypothyroidism (central hypothyroidism) is suggested by a normal to low normal TSH and low normal thyroid hormone, confirmed by the thyrotropin releasing hormone stimuation test (Indian J Endocrinol Metab 2011;15:S99)
Laboratory
Radiology Description
  • Pretibial myxedema:
    • Multiple imaging modalities may be helpful in diagnosis
    • Echo-Doppler of the lower legs may show venous and lymphatic insufficiency (An Bras Dermatol 2016;91:100)
    • Digital infrared thermal imaging, which detects surface temperature (Eur J Endocrinol 2011;164:605), shows an abnormally low focal temperature over the lower legs
    • High resolution ultrasonography shows composition changes in pretibial soft tissue (Eur J Endocrinol 2011;164:605)
  • Increased skin thickness is demonstrated by hypoechoic substance deposition in the cutaneous tissue, and blurred boundary lines between dermal and subcutaneous tissue
  • Prognostic Factors
    • Poor compliance with thyroid hormone replacement may lead to myxedema coma (Case Rep Endocrinol 2015;2015:169194)
    • Predictors of mortality in myxedema crisis or coma: bradycardia, hypotension, hypothermia, respiratory failure requiring mechanical ventilation, sepsis, intake of sedative drugs, high APACHE II score, SOFA (Sequential Organ Failure Assessment) scores greater than 6, and no response to treatment (J Thyroid Res 2011;2011:493462)
    Case Reports
    Treatment
    Gross Description
    Micro Description
    Positive Stains
    Electron Microscopy Description
    Videos