Pretibial myxedema or localized myxedema is an autoimmune manifestation of Graves' disease.

It may also occasionally occur in Hashimoto's thyroiditis.

Cases have been reported in  euthyroid patients with stasis dermatitis.

Almost all cases  are associated with relatively severe exophthalmos.

Smoking and chewing tobacco, are known risk factors for the development of pretibial myxedema.

Site: The lesions are located on the anterior aspect of the legs and rarely on the dorsum of the feet.

Clinical presentation: The lesions present as well circumscribed, yellowish, waxy nodules or plaques.

There is diffuse non-pitting edema.

The most severe variant, elephantiasis nostras verrucosa, is found in less than 1% of cases.

Microscopic features

- Mucin deposits in the dermis ( mainly in the mid and lower third of the dermis).

- Wide spaced collagen bundles due to increased amount of interstitial mucin

- Mild superficial perivascular chronic inflammatory cellular infiltrate is present.

- Dermal mucin is demonstrated by alcian blue stain.

Diagnosis of Pretibial myxedema is based on signs and typical pretibial skin lesions in association with a history of Graves' hyperthyroidism and ophthalmopathy. Skin biopsy is needed for confirmation of the clinical diagnosis.

Nodular pretibial myxedema.

Elephantiasic pretibial myxoedema: study of five cases

Preradial myxedema in a euthyroid male: A distinct rarity.

Pretibial myxedema.

Severe pretibial myxedema.

Graves' dermopathy on the big toe

Evidence for thyrotropin receptor immunoreactivity in pretibial connective tissue from patients with thyroid-associated dermopathy.