Pretibial myxedema is associated with which condition?

• A. Hashimoto thyroiditis
• B. Graves' disease
• C. Subacute thyroiditis
• D. Medullary thyroid carcinoma

Answer: (B)

Pretibial myxedema comes from autoimmune activity seen in Graves disease. In Graves, antibodies stimulate TSH receptors not only on the thyroid but also on fibroblasts in skin, especially in the shins, causing them to produce excess mucopolysaccharides (glycosaminoglycans). This leads to thickened, nonpitting edema and a characteristic pretibial skin change. It often appears alongside other Graves features like thyrotoxicosis and eye changes.

These skin changes aren’t typical of Hashimoto thyroiditis (hypothyroidism with different autoimmunity), subacute thyroiditis (painful, usually transient thyroiditis without mucopolysaccharide dermopathy), or medullary thyroid carcinoma (a thyroid cancer with calcitonin issues, not pretibial dermopathy).