Commonest cause of Cushings syndrome is
**Question:** Commonest cause of Cushing's syndrome is
A. Adrenal adenoma
B. Pituitary adenoma
C. Ectopic ACTH syndrome
D. Corticotropin-releasing hormone (CRH) deficiency
**Correct Answer:** C. Ectopic ACTH syndrome
**Core Concept:** Cushing's syndrome is a group of symptoms caused by long-term exposure to excessive cortisol levels. It is classified into two types: primary and secondary Cushing's syndrome.
**Why the Correct Answer is Right:** The correct answer, Ectopic ACTH syndrome (C), is the most common cause of Cushing's syndrome. ACTH (Adrenocorticotropic hormone) is produced by the pituitary gland and stimulates the adrenal cortex to produce cortisol. In ectopic ACTH syndrome, ACTH is secreted by a tumor outside the pituitary gland, leading to excessive cortisol production.
**Why Each Wrong Option is Incorrect:**
A. Adrenal adenoma (A) and D. Corticotropin-releasing hormone (CRH) deficiency (D) are not the primary causes of Cushing's syndrome. Adrenal adenomas are benign tumors in the adrenal gland, while CRH deficiency occurs when the hypothalamus does not produce sufficient CRH to stimulate the pituitary gland.
B. Pituitary adenoma (B) is a primary cause of Cushing's syndrome, as it produces excessive ACTH, leading to cortisol overproduction. However, it is not the most common cause of Cushing's syndrome.
**Clinical Pearl:** Ectopic ACTH syndrome should be suspected in patients with classic Cushing's symptoms but no pituitary adenoma, as it is more common in this scenario.
Diagnosis of Cushing's syndrome includes a combination of clinical examination, laboratory tests, and imaging studies. Treatment depends on the location and type of tumor causing the ACTH overproduction. Surgical removal of the tumor is usually curative in ectopic ACTH syndrome.