PRETIBIAL MYXEDEMA - FINAL MBBS REVISION

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OVERVIEW
Pretibial myxedema (PTM) or thyroid dermopathy is a rare condition occurring as part of thyroid disease. It represents localized lesions on the skin due to deposition of hyaluronic acid. Although PTM is mostly occurs in the pretibial area, it may occur anywhere on the skin, particularly ankle, dorsum of the foot, shoulders, upper back and neck. It almost always occurs in association with autoimmune thyroid disease

PATHOPHYSIOLOGY
PTM occurs due to localized deposition of hyaluronic acid in the skin and subcutaneous tissue.

It is postulated that cells called fibroblasts in the skin produce abnormally high amounts of glycosaminoglycans which get deposited in the skin. Other theories include the presence of abnormal cell mediated immunity (CMI). Since PTM frequently occurs at sites of injury, it is also postulated that trauma may stimulate the fibroblasts to proliferate

EPIDEMIOLOGY
It is a rare condition (< 5%) reported in patients with Grave’s disease and less often in patients with Hashimoto’s thyroiditis

Peak incidence is in the 5th-6th decades and it is found more often in females

CLINICAL FEATURES
Pretibial myxedema is commonly diagnosed 1-2 years after diagnosis of Grave’s disease. It is uncommon in the absence of Grave’s disease and is usually accompanied by Grave’s ophthalmopathy

Skin lesions and areas of non-pitting edema or firm, non-pitting, asymmetrical plaques or nodules appear on the anterior or lateral aspects of the legs particularly in sites of trauma in patients with Grave’s disease

DIFFERENTIAL DIAGNOSIS
• Erythema Nodosum
• Insect Bites
• Stasis dermatitis
• Lichen Myxedematosus
• Lichen Planus
• Lichen Simplex Chronicus
• Necrobiosis Lipoidica
• Necrobiosis lipoidica diabeticorum

DIAGNOSIS
In untreated Grave’s disease, TSH levels will be lower than normal with high levels of T3 and T4 thyroid hormones.
Thyrotropin-receptor antibodies (particularly TSIs) assays are almost always positive and confirm the diagnosis of Grave’s disease.

Although rarely done routinely, biopsy of the lesions show deposition of mucin (glycosaminoglycans) in the reticular dermis with weakening of collagen fibers. The mucin stains blue with Alcian-blue at a pH of 2.5 and colloidal iron stains; metachromasia is shown with toluidine blue stain

TREATMENT
The lesions of pretibial myxedema (PTM) are primarily of cosmetic concern to the patient, although severe forms may cause limb enlargement and impair normal function
• Surgical treatment is not advised as the scarring may aggravate the dermopathy
• Local application of corticosteroids (betamethasone, hydrocortisone gel, triamcinolone and fluocinonide) remains the mainstay of treatment.
• Compression wraps or stockings providing 20-40 mm Hg of pressure may help reduce swelling
• Newer treatment regimens that look promising but need further studies include octreotide, a somatostatin analog, and high-dose intravenous immunoglobulin (IVIG).

LONG TERM PROGNOSIS
Complications are rare and longterm prognosis is good. Spontaneous regression may occur in some patients and upto 25% patients undergo complete remission