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Hyaluronan, an example of a mucopolysaccharide.
The term myxedema has been applied to multiple medical conditions. Most commonly, it used used as a synonym for severe hypothyroidism.
It can also be used to describe a dermatologic condition associated with Graves' disease or a dermatologic condition in long-standing hypothyroidism in which mucopolysaccharides are deposited in the dermis.
Myxedema, in the first sense, is a form of hypothyroidism developing in the older child or adult. The clinical manifestations vary with the age of the onset of the deficiency. Clinical features of myxedema are characterized by a slowing of physical and mental activity. The initial symptoms include generalized fatigue, apathy, and mental sluggishness. Speech and intellectual functions become slowed. Patients with myxedema are unenthusiastic, cold intolerant, and frequently overweight. Decreased gastrointestinal motility results in constipation, and decreased sympathetic activity reduces sweating. The skin of these patients is often cool and pale. The patients often complain about shortness of breath and decreased exercise capacity. In addition, hypothyroidism promotes atherogenic profile, and serum levels of total cholesterol and low-density lipoprotein (LDL) are increased. Patients with unexplained increase in body weight or hypercholesterolemia should be assessed for potential hypothyroidism. Measurement of serum TSH level is the most sensitive screening test for this disorder. Myxedema (BrE: myxoedema) describes a specific form of cutaneous and dermal edema secondary to increased deposition of connective tissue components (like glycosaminoglycans, hyaluronic acid, and other mucopolysaccharides) in subcutaneous tissue as seen in various forms of hypothyroidism and Graves' disease (pretibial myxedema).:535 It is more common in women than in men.
The word originates from μύξα, taken from ancient Greek to convey 'mucus' or 'slimy substance' and ὁίδημα for swelling.
Signs and Symptoms 
Symptoms of Myxedema include thickening of the skin, and other symptoms associated with hypothyroidism, including fatigue, weight gain, depression, dry skin, and brittle hair, among others. The warning signs of myxedema include an intolerance to cold, low blood pressure, shortness of breath, lethargy and seizures. Someone suffering from untreated myxedema can become comatose and die. Nonpitting edema of the lower extremities is sometimes present. The findings from a thyroid examination are usually normal, but a goiter may be present in some patients. The presence of a scar on the neck might suggest postsurgical hypothyroidism and may be an important clue in the diagnosis of a patient who is comatose. A neurologic examination may reveal decreased reflex tendon relaxation and will invariably reveal altered mentation.
Early Symptoms 
• Hard stools or constipation • Increased sensitivity to cold • Fatigue or feeling slowed down • Heavier menstrual periods • Joint or muscle pain • Paleness or dry skin • Sadness or depression • Thin, brittle hair or fingernails • Weakness • Weight gain without trying
Late Symptoms 
• Weight gain • Slow speech • Pale skin • Swelling of leg (edema) • Muscular cramps • Shortness of breath • Absence of sweat • Secretion of milk from breast • Loss of hearing sensations • Reduced taste sensations • Lowered sense of smell • Absence of menstrual periods • Rise in menstrual bleeding
- Hyperthyroid myxedema is associated with hyperthyroidism, and typically presents in specific areas (pretibial myxedema and exophthalmos) and is related to high levels of TSH receptor stimulation and/or inflammation mounted against the TSH receptor itself. Myxedema of the lower legs (called pretibial myxedema), can occur in one to four percent of patients with Graves' disease—a condition that causes hyperthyroidism—or in patients with hypothyroid myxedema.
- Hypothyroid myxedema is used to describe the clinical syndrome secondary to hypothyroidism. Used in this way, myxedema can be considered the adult counterpart of cretinism.
- Myxedema coma is a condition which can occur with or without myxedema.
The increased deposition of glycosaminoglycan is not fully understood, however two mechanisms predominate.
- Exophthalmos in particular results from TSH receptor stimulation on fibroblasts behind the eyes which leads to increased glycosaminoglycan deposition. It is thought that many cells responsible for forming connective tissue react to increases in TSH levels.
- Secondarily, in autoimmune thyroid diseases lymphocytes react to the TSH receptor. Thus, in addition to the inflammation within the thyroid, any tissue with cells expressing the TSH receptor will likely experience lymphocytic infiltrates as well. The inflammation can cause tissue damage and scar tissue formation, explaining the deposition of glycosaminoglycans.
The increased deposition of glycosaminoglycans causes an osmotic edema and fluid collection.
See also 
- Vinay Kumar (2010). Robbins and Cotran Pathologic Basis of Disease. Saunder Elsevier. p. 1111. ISBN 978-1-4160-3121-5.
- James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0.
- BRS Pathology - A.S. Schneider, P.A. Szanto - 3rd edition - page 314
- Bertram Katzung (2012). Basic and Clinical Pharmacology. McGrawHill Lange. pp. 684, 691, 693. ISBN 978-0-07-176402-5.
- "Pretibial Myxedema", Retrieved on 2009-3-27
- "myxedema" at Dorland's Medical Dictionary
- "Hasihimotos Thyroiditis", Retrieved on 2009-3-27