Professional and Linguistic Assessments Board (PLAB) Practice Exam

In patients with Cushing's Disease, what type of tumor is typically responsible for increased ACTH secretion?

1. Cortical adenoma

2. Pituitary adenoma

3. Adrenal carcinoma

4. Neuroblastoma

The correct answer is: Pituitary adenoma

In patients with Cushing's Disease, the tumor typically responsible for increased secretion of ACTH (adrenocorticotropic hormone) is a pituitary adenoma. Cushing's Disease specifically refers to the condition resulting from excess cortisol due to an ACTH-secreting tumor in the pituitary gland. A pituitary adenoma is a benign tumor of the pituitary gland that can autonomously produce ACTH, leading to increased adrenal cortisol production. This mechanism is key in leading to the clinical manifestations associated with Cushing's, such as obesity, hypertension, and hyperglycemia, due to the excess cortisol. Understanding that Cushing's Disease arises from an excessive level of ACTH caused by a pituitary adenoma helps clarify the pathophysiology of the disease and its distinct features compared to other etiologies of Cushing's syndrome, which can arise from adrenal tumors or ectopic ACTH production. In this context, while adrenal carcinoma and neuroblastoma can also lead to excess cortisol but do so via different mechanisms and are not the cause of Cushing's Disease, the pituitary adenoma is quintessential for this specific diagnosis.