A 60-year-old woman with small cell carcinoma of the lung notes rounding of her face, upper truncal obesity, and muscle weakness. Physical examination reveals thin, wrinkled skin, abdominal striae, and multiple purpuric skin lesions. The patient’s blood pressure is 175/95 mm Hg. Laboratory studies will likely show elevated serum levels of which of the following hormones?

**Core Concept**
The patient's presentation is suggestive of Cushing's syndrome, a disorder caused by excess levels of cortisol, a steroid hormone produced by the adrenal gland. The symptoms and signs mentioned, including rounding of the face, upper truncal obesity, thinning of skin, and purpuric skin lesions, are characteristic of cortisol excess.

**Why the Correct Answer is Right**
The elevated blood pressure and skin manifestations are hallmarks of Cushing's syndrome. Cortisol promotes gluconeogenesis, lipolysis, and protein catabolism, leading to the characteristic redistribution of fat and muscle weakness. The thin, wrinkled skin is due to cortisol's inhibitory effect on collagen synthesis.

**Why Each Wrong Option is Incorrect**
**Option A:** Growth hormone (GH) is primarily involved in growth and development, particularly during childhood and adolescence. While GH can cause growth of soft tissues, it does not lead to the characteristic truncal obesity and skin changes seen in Cushing's syndrome.

**Option B:** Adrenocorticotropic hormone (ACTH) is a hormone produced by the pituitary gland that stimulates the release of cortisol from the adrenal gland. While elevated ACTH levels can cause Cushing's syndrome, the question asks for the hormone that is elevated, not the hormone that stimulates its release.

**Option D:** Insulin is a hormone involved in glucose metabolism, and its excess can cause hypoglycemia and weight gain, particularly in the abdominal region. However, it does not cause the characteristic skin changes and muscle weakness seen in Cushing's syndrome.

**Clinical Pearl / High-Yield Fact**
Cushing's syndrome is often associated with a "buffalo hump" - a collection of fat in the upper back, which is a classic sign of cortisol excess. This can be remembered using the mnemonic "CUSH" - Cushing's syndrome (C), Upper truncal obesity (U), Skin changes (S), and Hump (H).

**Correct Answer:** C. Cortisol

✓ Correct Answer: B. Coicotropin