Pretibial Myxedema (Thyroid Dermopathy)

What pretibial myxedema is

In Graves' disease, the immune system makes antibodies against the TSH receptor, which over-stimulate the thyroid. The same receptor is found on fibroblasts, the cells that make connective tissue in the skin and behind the eyes. When these antibodies and immune cells activate skin fibroblasts, they produce large amounts of glycosaminoglycans, especially hyaluronic acid. These water-loving molecules swell the deeper skin layer, making it thick and firm.

The shins are thought to be affected because of pressure, gravity and the slower circulation in the lower legs. Pretibial myxedema is part of a group of Graves' disease features outside the thyroid:

• Thyroid eye disease (Graves' orbitopathy), present in almost all people with dermopathy
• Thyroid dermopathy (pretibial myxedema)
• Thyroid acropachy: swelling of the fingers and toes with clubbing, the rarest

The name can be confusing. "Myxedema" also describes the generalized puffy skin of severe hypothyroidism, which is a different condition. Pretibial myxedema can occur when the thyroid is overactive, normal or underactive after treatment.

Symptoms and appearance

• Raised, firm plaques or nodules on the front of the shins, usually on both legs
• Skin that looks waxy and shiny, with enlarged hair follicles and pores, like orange peel (peau d'orange)
• Color ranging from skin-toned to pink, purplish, brown or yellow
• Non-pitting swelling: pressing a finger in does not leave a dent
• Sometimes thicker hair over the plaques
• Usually painless, though it can itch
• Less commonly on the tops of the feet, toes, ankles, arms, shoulders or previous scars

Forms

Risk factors

• Graves' disease, especially when long-standing
• Severe thyroid eye disease
• Smoking, which worsens both eye and skin disease
• High levels of TSH receptor antibodies
• Leg injury or trauma, which can trigger lesions at that site

It usually appears 1 to 2 years after Graves' disease is diagnosed, often after eye disease, but can occasionally come first.

Diagnosis

Most cases are diagnosed by a doctor recognizing the typical appearance in someone with Graves' disease and eye signs. Tests include:

• Thyroid function tests and TSH receptor antibodies (TRAb), which are usually high
• Skin biopsy, only if the diagnosis is uncertain. It shows mucin deposits in the dermis. Biopsy wounds can heal poorly in affected skin.

Conditions that can look similar include lymphedema, stasis dermatitis from poor vein circulation, cellulitis, necrobiosis lipoidica in diabetes, and other forms of skin mucinosis.

Treatment

Treating the overactive thyroid itself does not reliably improve pretibial myxedema, but keeping thyroid levels normal is still important. Avoiding hypothyroidism after treatment may matter, because high TSH levels can worsen the dermopathy.

Mild, painless cases may not need treatment. Options include:

• High-potency topical corticosteroids, often applied under plastic wrap (occlusion) overnight for several weeks. This is the first-line treatment.
• Steroid injections directly into plaques or nodules.
• Compression stockings or wraps to reduce swelling, sometimes with lymphatic drainage therapy.
• Stopping smoking, which also protects the eyes.
• For severe or resistant disease: treatments such as pentoxifylline, IV immunoglobulin, rituximab, octreotide or, more recently, teprotumumab (an antibody used for thyroid eye disease) have been reported to help in some people. These are specialist options with limited evidence.
• Surgical removal is generally avoided because lesions can recur at the scar.

Outlook

Pretibial myxedema is not dangerous. In about half of people with mild disease, it partly or completely fades over several years. Severe, elephantiasic forms are less likely to resolve. Its presence suggests more active autoimmune disease, so regular eye checks are recommended.

Frequently asked questions

What does pretibial myxedema look like?

It looks like thick, firm, raised patches or lumps on the front of the shins, often skin-colored, pink, brown or yellowish. The surface is waxy with large pores, like orange peel. Pressing on it does not leave a dent.

Is pretibial myxedema only in Graves' disease?

Almost always. Most people with pretibial myxedema have Graves' disease, usually with thyroid eye disease. It is rarely seen with Hashimoto's thyroiditis. It is different from the generalized puffy skin of severe hypothyroidism, despite the similar name.

Does pretibial myxedema go away?

Mild cases often improve or fade slowly over years, especially with treatment. Severe, long-standing cases are less likely to resolve fully. Steroid treatment, compression and stopping smoking improve the chances of improvement.

Will treating my thyroid cure pretibial myxedema?

Usually not by itself. The skin changes are driven by the autoimmune antibodies rather than the thyroid hormone level. Keeping your thyroid levels normal is still important, but the skin usually needs its own treatment, such as steroid creams under occlusion.

Is pretibial myxedema painful?

Usually not. It is typically painless, though it can itch or feel tight, and severe forms can make shoes or socks uncomfortable. New pain, heat and redness suggest a different problem such as infection and should be checked.