A 58-year-old woman from rural India presents with progressive fatigue, cold intolerance, and weight gain over 6 months. On examination, she has the clinical findings marked **A** in the diagram: puffy facies, periorbital edema, loss of lateral eyebrows, and macroglossia. Her serum TSH is 45 mIU/L and free T4 is 0.8 ng/dL. Which of the following best explains the pathophysiology of the cutaneous and tissue manifestations marked **A**?

Explanation

## Why option 1 is right The clinical findings marked **A** — puffy facies, periorbital edema, macroglossia, and loss of lateral eyebrows — constitute the classic presentation of myxedema in severe, long-standing hypothyroidism. The pathophysiology is well-established: thyroid hormone deficiency impairs fibroblast metabolism, leading to accumulation of hydrophilic glycosaminoglycans (primarily hyaluronic acid and chondroitin sulfate) in the dermis, subcutaneous tissues, and other organs. These GAGs bind water, producing the characteristic NON-PITTING, doughy, myxedematous edema that distinguishes this condition from simple fluid retention. This mechanism explains all the features shown: the puffy facies and periorbital edema result from GAG accumulation in facial tissues, macroglossia from GAG infiltration of the tongue, and the loss of lateral eyebrows (madarosis/Queen Anne sign) reflects the broader metabolic derangement of hypothyroidism. (Harrison 21e Ch 376) ## Why each distractor is wrong - **Option 2 (Immune complexes and complement)**: While Hashimoto thyroiditis (the most common cause of hypothyroidism in iodine-sufficient regions) is autoimmune with anti-TPO and anti-thyroglobulin antibodies, the cutaneous manifestations of myxedema are NOT due to immune complex deposition or vasculitis. The edema is non-pitting and tissue-infiltrative, not inflammatory in nature. - **Option 3 (Lymphocytic infiltration and granulomas)**: Lymphocytic infiltration occurs in the thyroid gland itself in Hashimoto thyroiditis, not in the dermis. Granulomatous dermatitis is not a feature of myxedema. This describes thyroid pathology, not the skin manifestations marked **A**. - **Option 4 (Lipid-rich foam cells and xanthomas)**: While hypothyroidism does cause hypercholesterolemia (from reduced LDL receptor activity), xanthomatous deposits are not the mechanism of myxedematous edema. Xanthomas would present as firm nodules, not the doughy, non-pitting edema and facial puffiness seen here. **High-Yield:** Myxedema = GAG infiltration → non-pitting edema; distinguish from pitting edema (heart/liver/kidney disease) and from immune-mediated swelling (Graves ophthalmopathy). [cite: Harrison 21e Ch 376 — Hypothyroidism; clinical features and pathophysiology of myxedema]