Pretibial myxedema

Specialty: Endocrine and metabolic.

• thyroid dermopathy
• Graves' pretibial indurated plates
• circumscribed myxedema

Why it occurs

• Graves-Basedow disease (immune reaction mediated by TSH receptor-stimulating antibodies that activate fibroblasts of the pretibial dermis, inducing a massive accumulation of hyaluronic acid and chondroitinsulfate)
• Hashimoto's thyroiditis (rarely, associated with elevated antibody levels and severe hypothyroid state)
• Total thyroidectomy for toxic goiter with poor control and extreme oscillations of thyroid function in the postoperative period

Initial workup

Determination of antibodies against the TSH receptor (TRAb/TSI); plasma thyroid hormones (TSH, free T4 and free T3); skin biopsy of the lesion demonstrating abundant acidic mucin deposition in the dermis with separation of the collagen bundles without prominent inflammatory cellular infiltrate; and color Doppler ultrasound of the lower limbs to rule out chronic venous insufficiency or deep vein thrombosis.

Standard management

• Clobetasol propionate 0.05% — ultra-high potency topical corticosteroid applied under plastic film occlusion overnight to reduce fibroblast activity and mucopolysaccharide synthesis
• Methylprednisolone — periodic intralesional injections in hypertrophic and painful pretibial plaques resistant to topical corticosteroids
• Pentoxifylline — oral agent 400 mg three times a day that inhibits in vitro glycosaminoglycan synthesis by TRAb-stimulated pretibial fibroblasts
• Rituximab — anti-CD20 monoclonal antibody considered in exceptional cases of rapidly progressive Graves' orbitopathy and dermopathy