**Core Concept**
Cushing syndrome is a rare endocrine disorder caused by prolonged exposure to excess cortisol, leading to various systemic effects. This condition can result from various etiologies, including endogenous production (e.g., adrenal tumors) or exogenous administration (e.g., glucocorticoid medications). The pathophysiology involves the disruption of the hypothalamic-pituitary-adrenal (HPA) axis.

**Why the Correct Answer is Right**
The correct answer involves understanding the HPA axis and the consequences of cortisol excess. Cortisol stimulates gluconeogenesis, lipolysis, and protein catabolism, leading to characteristic clinical features such as weight gain, hypertension, and hyperglycemia. In Cushing syndrome, the increased cortisol production disrupts the normal feedback inhibition of the HPA axis, resulting in elevated adrenocorticotropic hormone (ACTH) levels.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be incorrect if it suggests a different pathophysiological mechanism or etiology for Cushing syndrome.
**Option B:** This option might be incorrect if it implies that Cushing syndrome is caused by a single factor or is not a complex endocrine disorder.
**Option C:** This option might be incorrect if it incorrectly identifies the primary cause or consequence of Cushing syndrome.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of Cushing syndrome is the presence of purple striae, which are a result of skin thinning and atrophy due to prolonged cortisol exposure. These striae are a distinctive clinical finding that can aid in the diagnosis of Cushing syndrome.

**Correct Answer: C.**