Pretibial myxedema: pathophysiology and treatment options.

Pretibial myxedema or localized myxedema or thyroid dermopathy is an autoimmune manifestation of Graves' disease. It also occasionally occurs in Hashimoto's thyroiditis. Lesions of thyroid dermopathy are usually asymptomatic and have only cosmetic importance. Advanced forms of dermopathy are associated with elephantiasis or thyroid acropachy. Almost all cases of thyroid dermopathy are associated with relatively severe ophthalmopathy. Usually ophthalmopathy appears first and dermopathy much later. All patients with localized myxedema have high serum concentrations of thyroid-stimulating hormone receptor antibodies, indicating the severity of the autoimmune condition. Occurrence of thyroid dermopathy in areas other than pretibial skin indicates a systemic process. Similar to Graves' ophthalmopathy, thyroid-stimulating hormone receptors in the connective tissue may be the antigen responsible for the immune process. Both humoral and cellular immune mechanisms are involved in the stimulation of fibroblasts and the production of large amounts of glycosaminoglycans. 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. In mild cases that do not require treatment, 50% of patients achieve complete remission after several years. Severe cases that receive topical corticosteroids or other therapies do not have a better outcome than untreated milder cases. Current treatment modalities for thyroid dermopathy and acropachy are at best palliative. Better and safer means of immunomodulation are needed.