A 42-year-old woman with Graves disease (TSI-positive, treated with carbimazole and now on levothyroxine after thyroidectomy) presents with bilateral, non-pitting, indurated, waxy plaques on the anterolateral shins with a characteristic peau d'orange surface and prominent follicular ostia. She also has bilateral proptosis and digital clubbing. The structure marked **B** in the diagram shows the characteristic skin manifestation. Which of the following best describes the pathophysiology underlying this lesion?
A. Immune-mediated collagen necrosis with lipid deposition in the dermis, associated with diabetes mellitus
B. Deposition of glycosaminoglycans (hyaluronic acid) in the dermis driven by TSH-receptor antibodies cross-reacting with dermal fibroblasts
C. Chronic inflammation with lichenification secondary to repeated scratching and impaired venous return
D. Chronic venous insuffocation leading to lipodermatosclerosis and dermal fibrosis
Explanation
Why option 1 is correct
The structure marked B represents pretibial myxedema (thyroid dermopathy), an infiltrative dermopathy pathognomonic to Graves disease. The hallmark pathophysiology is glycosaminoglycan (predominantly hyaluronic acid) deposition in the dermis, driven by TSH-receptor antibodies (TRAb) that cross-react with fibroblasts in dermal connective tissue. Histologically, this produces widely separated collagen bundles with mucin deposition in the mid-to-deep dermis, staining positive with colloidal iron or Alcian blue. This occurs in 1–5% of Graves disease patients, almost always with concurrent ophthalmopathy and high TRAb titers, and can paradoxically appear after biochemical euthyroidism is achieved (Bolognia Dermatology 5e; Endocrine Reviews on Graves Orbitopathy 2024).
Why each distractor is wrong
Option 2 (Chronic venous insufficiency): This describes lipodermatosclerosis (marked A in the diagram), not thyroid dermopathy. Venous insufficiency produces fibrosis and hemosiderin deposition, not glycosaminoglycan accumulation, and is not associated with Graves disease or TSI positivity.
Option 3 (Collagen necrosis with lipid deposition): This describes necrobiosis lipoidica diabeticorum (marked C in the diagram), a diabetic dermopathy characterized by immune-mediated collagen necrosis and lipid deposition. It is not driven by TSH-receptor antibodies and is not a feature of Graves disease.
Option 4 (Lichenification from scratching): This describes stasis dermatitis with secondary lichen simplex chronicus (marked D in the diagram), a consequence of chronic venous insufficiency and repeated trauma. It lacks the characteristic glycosaminoglycan deposition and TSI-mediated pathophysiology of thyroid dermopathy.
High-YieldNEET PG
Pretibial myxedema is a TSI-driven infiltrative dermopathy with hyaluronic acid deposition; it occurs in ~1–5% of Graves disease, almost always with ophthalmopathy, and can appear even after euthyroidism is restored.
Bolognia Dermatology 5e; Endocrine Reviews on Graves Orbitopathy 2024
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