This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Most common cause of hyperparathyroidism: March 2009 
Select and explain. 
A. Carcinoma, B. Hyperplasia, C. Adenoma, D. Familial isolated hyperparathyroidism
C: Adenoma
Answer: C: Adenoma 
Explanation: Ans. C: Adenoma Hyperparathyroidism causes hypercalcemia through the excessive secretion of parathyroid hormone, usually by an adenoma (benign tumors) of the parathyroid glands (nearly 80%). Chief cell parathyroid hyperplasia accounts for nearly 15% cases.