This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
Which of the following statements about Cushing's disease is true? 
Select and explain. 
A. Serum adrenocoicotropin (ACTH) levels usually are low, B. Pituitary microadenoma usually is present, C. There is a high incidence of nonendocrine tumors, D. Nonsuppression of coisol production by the high-dose dexamethasone suppression test is a characteristic finding
B: Pituitary microadenoma usually is present
Answer: B: Pituitary microadenoma usually is present 
Explanation: Cushing's syndrome is due to increased adrenal coisol production, regardless of aetiology.Cushing's disease usually is caused by a pituitary microadenoma producing high adrenocoicotropin (ACTH) levels.In most patients, coisol levels would be suppressed as a result of the high-dose dexamethasone suppression test.Transsphenoidal microsurgical removal of the microadenoma is the treatment of choice in most centres.