The exact mechanism for the deposition of glycosaminoglycans in the skin of the lower legs is uncertain. Pretibial myxoedema is nearly always associated with Graves disease. Graves disease is an autoimmune disorder that affects the thyroid gland in which there are antibodies to TSH-R activate the receptor, often causing an increase in circulating thyroid hormone.
This is hyperthyroidism or thyrotoxicosis. Symptoms of thyrotoxicosis include weight loss, palpitations, sweating hyperhidrosis , and tremors.
Classic triad of Graves disease Pretibial myxoedema. Pretibial myxoedema can appear before, during, or after the thyrotoxic state. It is not related to thyroid function. It is generally seen 12—24 months after diagnosis. Pretibial myxoedema Pretibial myxoedema in Graves disease. Diagnosis of pretibial myxoedema is made by taking a history and finding characteristic clinical appearance on examination of the patient. Skin biopsy is rarely necessary for diagnosis, especially if there is a history of hyperthyroidism, or Graves ophthalmopathy.
If a biopsy is done, histopathology typically shows deposition of mucin glycosaminoglycans throughout the dermis and subcutis. Deposited mucin promotes dermal oedema by promoting the retention of fluid in the skin. The biopsy also shows attenuation of collagen fibres; they may be frayed, fragmented and widely separated. Stellate star-shaped fibroblasts are often observed, but the number of fibroblasts remains normal. Often a mild, superficial lymphocytic infiltrate around blood vessels is seen, and the overlying epidermis may show hyperkeratosis increased scale.
The prognosis is generally quite good. Most patients with asymptomatic pretibial myxoedema do not require treatment or follow-up. Even with more severe disease, it resolves in more than half of patients after several years. The elephantiasic form is the most difficult to treat, and is the least likely to clear up. The likelihood of remission depends on the severity of the initial disease rather than its treatment. See smartphone apps to check your skin. Books about skin diseases Books about the skin Dermatology Made Easy book.
Cutaneous mucinosis is a heterogeneous group of diseases caused by an abnormal accumulation of dermal mucin, an amorphous substance composed mainly of hyaluronic acid and glycosaminoglycans, uncommon in the pretibial region. Dermal mucinosis as a sign of venous insufficiency. J Cutan Pathol. Even though the terms pretibial myxedema and pretibial mucinosis have been frequently used as synonyms, pretibial myxedema is a kind of mucinosis associated with autoimmune thyroid disease.
Pretibial Myxedema - Pathophysiology and Treatment Option. Am J Clin Dermatol. Although usually limited to the pretibial area, it has also been described in other regions, with terms like thyroid dermopathy or localized myxedema being considered the most appropriate ones. In initial case reports of pretibial mucinosis in patients with normal thyroid function it was still questioned if they would develop thyroid disease in the future.
Euthyroid pretibial myxedema. Am J Med. Int J Dermatol. Later other conditions that could lead to pretibial mucin deposition, among those trauma, venous insufficiency, lymphedema and obesity were described. In Kim et al reported a case of pretibial mucinosis in a patient without evidence of autoimmune thyroid disease. This patient presented the symptom after a car crash trauma with subsequent venous insufficiency, lymphedema and recurring cellulitis on the lower limbs.
A case of pretibial mucinosis without thyroid disease. J Dermatol. In Tokuda et al reported 3 cases of pretibial mucinosis in patients with morbid obesity and chronic edema of lower limbs.
Chronic obesity lymphoedematous mucinosis: three cases of pretibial mucinosis in obese patients with pitting oedema. Br J Dermatol. In Rongioletti et al described 5 patients with similar symptoms to the ones described by Tokuda. Obesity - associated lymphoedematous mucinosis. In Pugashetti, R et al described two cases of dermal mucinosis in the lower extremities as a sign of venous insufficiency. The mechanism of dermal mucin accumulation in a stasis context is still uncertain, but hypoxia may be a determinant.
Venous insufficiency leads to decreasing levels of oxygen and extravasation of plasma proteins, such as albumin and coagulation factors. Formation of microthrombi worsens ischemia and triggers angiogenesis, while albumin and other plasma proteins increase production of mucopolysaccharides. Stasis in protein-rich lymph fluid in chronic lymphedema may stimulate mucin production in a similar way. Localization in the pretibial area relates to mechanical factors and dependent position.
Diagnosis of thyroid dermopathy is based on signs and typical pretibial skin lesions in association with a history of Graves' hyperthyroidism and ophthalmopathy. In some cases, skin biopsy is needed for confirmation. The lesions are usually mild and are overshadowed by more symptomatic ophthalmopathy.
Most cases of thyroid dermopathy do not require any therapy. In mildly severe symptomatic cases and when there is cosmetic concern, topical corticosteroids applied under occlusive dressing are beneficial. In more severe cases, systemic immunomodulation may be necessary; however, conclusive evidence for long-term efficacy of these modalities is lacking. When significant edema and elephantiasis are present, local compressive therapy may have added benefit.
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