Myxedema: Difference between revisions

Myxedema
Myxedema
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Myxedema (British English: myxoedema) describes a specific form of cutaneous and dermal edema secondary to increased deposition of connective tissues (like glycosaminoglycans, hyaluronic acid, and other mucopolysaccharides) as seen in various forms of hypothyroidism and Graves' disease.^[1]^: 535

Terminology

The word originates from [μύξα,] Error: {{Lang}}: text has italic markup (help) taken from ancient Greek to convey 'mucus' or 'slimy substance' and [ὁίδημα] Error: {{Lang}}: text has italic markup (help) for swelling.

The term can be the cause of some confusion, because it can be used both in the context of hyperthyroid states and hypothyroid states.

Hyperthyroid: Myxedema 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 1-4% of patients with Graves' disease - a condition that causes Hyperthyroidism^[2].

Hypothyroid: Myxedema is also used to describe the clinical syndrome secondary to hypothyroidism. Symptoms can include depression, mental slowness, weakness, bradycardia, fatigue, hypothermia, alopecia, and many others (see symptoms of severe hypothyroidism). Used in this way, Myxedema can be considered the adult counterpart of cretinism.^[3]

Causes

The increased deposition of glycoaminoglycans 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 glycoaminoglycan 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 cell that expresses the TSH receptor will likely experience lymphocytic infiltrates as well. The inflammation can cause tissue damage and scar tissue formation explaining the deposition of glycoaminoglycans.

The increased deposition of glycoaminoglycans causes an osmotic edema and fluid collection.

Hashimoto's thyroiditis is the most common cause of myxodema in the United States^[4].

References

^ James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0. {{cite book}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
^ "Pretibial Myxedema", Retrieved on 2009-3-27
^ "myxedema" at Dorland's Medical Dictionary
^ "Hasihimotos Thyroiditis", Retrieved on 2009-3-27

This template is no longer used; please see Template:Endocrine pathology for a suitable replacement

[Andrews-1] James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0. {{cite book}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)

[thedoctorsdoctor_pretibial_myxedema-2] "Pretibial Myxedema", Retrieved on 2009-3-27

[3] "myxedema" at Dorland's Medical Dictionary

[4] "Hasihimotos Thyroiditis", Retrieved on 2009-3-27

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[2]

[3]

[4]

@@ Line 2: / Line 2: @@
 {{Infobox Disease |
   Name           = Myxoedema |
-  Image          = Pretibial-myxedema-16.jpg|
+  Image          = Hyaluronan.png |
-  Caption        = [[shin|Shins]] of a patient with myxedema showing characteristic orange peel appearance|
+  Caption        = [[Hyaluronan]], an example of a [[mucopolysaccharide]]. |
   ICD10          = {{ICD10|E|03|9|e|00}} |
   ICD9           = {{ICD9|244.9}} |
@@ Line 15: / Line 15: @@
   MeshID         = D009230 |
 }}
-Hypothyroid type '''myxedema''' (British English: '''myxoedema''') describes a specific form of [[cutaneous]] and [[dermal]] non-pitting [[edema]] secondary to increased deposition of [[connective tissue]] matrix components (like [[glycosaminoglycan]], [[hyaluronic acid]], and other [[mucopolysaccharide]]s). In [[Graves' disease]] the myxedema is secondary to lymphocytic infiltrate and secondary swelling from inflammatory reactions and is typically located in the periorbital tissues, [[extraocular muscles]], and in the lower legs, mostly below the knee ([[pretibial myxedema]]).<ref name="Andrews">{{cite book |author=James, William D.; Berger, Timothy G.; et al. |title=Andrews' Diseases of the Skin: clinical Dermatology |publisher=Saunders Elsevier |location= |year=2006 |pages= |isbn=0-7216-2921-0 |oclc= |doi= |accessdate=}}</ref>{{rp|535}} While both hyper- and hypo- thyroidism have forms of myxedema their etiologies are pathophysiologically distinct.
+'''Myxedema''' (British English: '''myxoedema''') describes a specific form of [[cutaneous]] and [[dermal]] [[edema]] secondary to increased deposition of [[connective tissue]]s (like [[glycosaminoglycan]]s, [[hyaluronic acid]], and other [[mucopolysaccharide]]s) as seen in various forms of [[hypothyroidism]] and [[Graves' disease]].<ref name="Andrews">{{cite book |author=James, William D.; Berger, Timothy G.; et al. |title=Andrews' Diseases of the Skin: clinical Dermatology |publisher=Saunders Elsevier |location= |year=2006 |pages= |isbn=0-7216-2921-0 |oclc= |doi= |accessdate=}}</ref>{{rp|535}}
 ==Terminology==
-The word originates from {{lang|grc|''μύξα,''}} taken from ancient Greek to convey 'mucus' or 'slimy substance' and {{lang|grc|''ὁίδημα''}} for swelling. Myxedema is also a clinical state that is intermediate between cretinism of children and hypothyroidism of adults. Clinical features of myxedema are characterized by a slowing of physical and mental activity. Symptoms include [[Depression (mood)|depression]], mental sluggishness, listlessness, cold intolerance, obesity, [[constipation]] and decreased sweating secondary to decreased [[sympathetic nervous system]] output, and also reduced [[cardiac output]] that contributes to shortness of breath and exercise intolerance. <ref>Pathological Basis of Disease, 8th Ed. Robbins and Contran, 2010. ISBN: 978 1 4377 0792 2</ref>
+The word originates from {{lang|grc|''μύξα,''}} taken from ancient Greek to convey 'mucus' or 'slimy substance' and {{lang|grc|''ὁίδημα''}} for swelling.
+The term can be the cause of some confusion, because it can be used both in the context of hyperthyroid states and hypothyroid states.
-The term can be a cause for confusion but it should not be confused with a form of myxedema seen in [[Graves' disease]] and hyperthyroid states which does '''not''' include the mental sluggishness and listless state of the aforementioned hypothyroid myxedema. In the context of hyperthyroidism, ''pretibial'' myxedema typically presents in the lower limb (below the knee) and periorbital myxedema leads to the [[exophthalmos]] (bulging eyes), both of which include autoimmune mechanisms and T cells that are not a contributing factor in hypothyroid myxedema.
+* [[Hyperthyroid]]: Myxedema typically presents in specific areas ([[pretibial myxedema]] and [[exophthalmos]]) and is related to high levels of [[Thyroid-stimulating hormone|TSH]] receptor stimulation and/or inflammation mounted against the [[Thyroid-stimulating hormone|TSH]] receptor itself.  Myxedema of the lower legs (called [[pretibial myxedema]]), can occur in 1-4% of patients with [[Graves' disease]] - a condition that causes '''[[Hyperthyroidism]]'''<ref name="thedoctorsdoctor pretibial myxedema">[http://www.thedoctorsdoctor.com/diseases/pretibial_myxedema.htm "Pretibial Myxedema"], Retrieved on 2009-3-27</ref>.
+* [[Hypothyroid]]: Myxedema is also used to describe the clinical syndrome secondary to [[hypothyroidism]]. Symptoms can include depression, mental slowness, weakness, bradycardia, fatigue, [[hypothermia]], [[alopecia]], and many others (see [[Hypothyroidism#Symptoms|symptoms of severe hypothyroidism]]). Used in this way, Myxedema can be considered the adult counterpart of [[cretinism]].<ref>{{DorlandsDict|five/000069929|myxedema}}</ref>
 ==Causes==
+The increased deposition of [[glycoaminoglycans]] is not fully understood, however two mechanisms predominate.
-[[image:Hyaluronan.png|thumb|right|[[Hyaluronan]], an example of a [[mucopolysaccharide]].]]
+* Exophthalmos in particular results from [[Thyroid-stimulating hormone|TSH]] receptor stimulation on fibroblasts behind the eyes which leads to increased glycoaminoglycan deposition. It is thought that many cells responsible for forming connective tissue react to increases in [[Thyroid-stimulating hormone|TSH]] levels.
-'''Hypothyroidism'''
+* Secondarily, in autoimmune thyroid diseases lymphocytes react to the [[Thyroid-stimulating hormone|TSH]] receptor. Thus, in addition to the inflammation within the thyroid any cell that expresses the [[Thyroid-stimulating hormone|TSH]] receptor will likely experience lymphocytic infiltrates as well. The inflammation can cause tissue damage and scar tissue formation explaining the deposition of glycoaminoglycans.
-* The skin in hypothyroidism is cool and dry. Normally, the skin contains a variety of proteins complexed with polysaccharides, chondroitin sulfuric acid and hyaluronic acid. In hypothyroidism, these complexes accumulate, promoting sodium and water retention and producing a characteristic diffuse, non-pitting puffiness of the skin (myxedema). The person's face appears puffy, with coarse features. Similar accumulation of mucopolysaccharides in the larynx may lead to hoarseness. The hair is brittle and lacking luster, and there is frequently loss of body hair, particularly over the scalp and lateral thirds of the eyebrows. If the thyroid hormone is replaced therapeutically, the protein complexes are mobilized and a diuresis ensues and the myxedema resolves. Carotenemia (yellow-orange skin) can occur because thyroid hormone is needed by the liver to convert carotene to vitamin A. In the absence of sufficient hormone, carotene accumulates in the bloodstream and skin.
-* In long-standing hypothyroidism a condition called myxedema coma may occur. Patients have typical myxedematous facies and skin, bradycardia, hypothermia, alveolar hypoventilation and severe obtundation or coma. This condition is usually precipitated by an intercurrent illness such as an infection or stroke or by a medication such as a sedative-hypnotic. The mortality rate approaches 100% unless myxedema coma is recognized and treated promptly.<ref>Pathophysiology of Diseae, An Introduction to Clinical Medicine. Stephen McpPhee and William Ganong</ref>
+The increased deposition of glycoaminoglycans causes an osmotic edema and fluid collection.
-[[Hashimoto's thyroiditis]] is the most common cause of myxedema in the United States<ref>[http://www.medicinenet.com/hashimotos_thyroiditis/article.htm "Hasihimotos Thyroiditis"], Retrieved on 2009-3-27</ref>. In third world countries [[iodine deficiency]] is a significant contributor to hypothyroidism.
+[[Hashimoto's thyroiditis]] is the most common cause of myxodema in the United States<ref>[http://www.medicinenet.com/hashimotos_thyroiditis/article.htm "Hasihimotos Thyroiditis"], Retrieved on 2009-3-27</ref>.
 ==See also==