Pretibial myxedema, which is also called thyroid dermopathy and localized myxedema, nearly always occurs in patients who have severe Graves’ ophthalmopathy, an eye disease also known as thyroid eye disease or TED.
Autoimmune Nature
The underlying disease process in pretibial myxedema is not well known. Pretibial myxedema is thought to be caused by the activation of dermal fibroblasts, the basic cell precursors that make up our skin cells and by the stimulation of connective tissue cells by TSH receptor antibodies. High levels of the thyroid hormone T3, high levels of stimulating and blocking TSH receptor antibodies, and immune system chemicals known as cytokines are also suspected of contributing to the disease process. In PTM, activated fibroblasts tend to produce excess deposits of hyaluronic acid, and it is this imbalance in glycosaminoglycan proteins that leads to dermal changes.
Who is Affected?
It’s estimated that about 4 percent of patients with thyroid eye disease develop pretibial myxedema. Of these, about 25 percent of patients go on to develop the extreme form of PTM known as thyroid acropachy, which is a form of elephantiasis. Women with Graves’ disease are 3.5 times more likely to develop PTM than men. The peak incidence of PTM occurs during the 5th to 6th decades of life.
PTM can also rarely develop in patients with Graves’ disease who have no evidence of TED. In addition, PTM can occur after surgical or radioiodine treatment of Graves’ disease, and it can also rarely occur in patients with Hashimoto’s thyroiditis and stasis dermatitis.
Symptoms
Pretibial myxedema is characterized by localized thickening of the skin, primarily in the pretibial region, including the shins and lower legs. The upper legs, arms, shoulders, back, torso, neck, ears, and face may also be affected. The skin thickening may be accompanied by a non-pitting edema, waxy lesions, dryness, and itching. The lesions in PTM are considered to primarily be a cosmetic nuisance. However, if lesions compress nerves or blood vessels, symptoms can include pain and impaired blood circulation.
Diagnosis
PTM is suggested when the characteristic skin changes are seen in patients with a history of Graves’ disease or Graves’ ophthalmopathy. A skin biopsy is required to definitively confirm PTM. Biopsy reveals excess hyaluronic acid although there is no increase in fibroblasts. In longstanding PTM, a secondary hyperkeratosis may occur, which causes a crusting of lesions.
Treatment
Most patients with PTM do not require treatment as lesions are likely to be mild. In 50 percent of patients with mild cases, symptoms spontaneously resolve within 3-5 years. When treatment is required, topical applications of corticosteroids are applied to the affected areas and covered with cellophane or other occlusive dressings. When areas other than the pretibial region are affected, systemic involvement is suspected and oral corticosteroids may be needed. In severe cases of PTM, treatment with intravenous immunoglobulins is reported to show benefits.
Resource:
Elaine Moore, Graves' Disease, A Practical Guide, McFarland and Company, Jefferson, NC:2000.
