A 42-year-old woman presents with progressive central obesity, facial plethora, and proximal muscle weakness over 18 months. On examination, the structure marked **D** in the diagram is noted—broad, purple striae measuring 1.5 cm in width over the abdomen and axillae. Her blood pressure is 158/94 mmHg, and fasting glucose is 142 mg/dL. Which of the following best explains the pathophysiology of the finding marked **D**?

Explanation

## Why Option 1 is right The wide purple striae marked **D** are a pathognomonic sign of Cushing syndrome. They occur because chronic glucocorticoid excess causes collagen depletion in the dermis, rendering the skin thin and unable to resist normal stretch forces. The striae are characteristically broad (>1 cm) and purple—distinguishing them from pregnancy striae, which are narrower and pink/white. This finding reflects the catabolic effect of excess cortisol on connective tissue and is a hallmark of chronic glucocorticoid exposure (Harrison 21e Ch 386; Williams Textbook of Endocrinology 14e). ## Why each distractor is wrong - **Option 2**: While elevated ACTH can cause hyperpigmentation (especially in ectopic ACTH syndrome), hyperpigmentation manifests as darkening of skin and mucous membranes, not as purple striae. Striae are a structural skin finding, not a pigmentary one. - **Option 3**: Growth hormone elevation causes acanthosis nigricans, skin thickening, and coarse features—not striae. GH excess does not cause the collagen depletion seen in Cushing syndrome. - **Option 4**: Mechanical trauma from weight gain alone does not explain the purple color or the specific pathophysiology. Pregnancy striae, which also occur with rapid stretch, are pink/white and narrower because the skin retains normal collagen architecture. **High-Yield:** Purple striae >1 cm on abdomen, axillae, and thighs are pathognomonic for Cushing syndrome; they reflect cortisol-induced collagen depletion, not just mechanical stretch. [cite: Harrison 21e Ch 386; Williams Textbook of Endocrinology 14e]