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: Medicine
The most common cause of hyperparathyroidism is 
Select and explain. 
A. Parathyroid adenoma, B. Parathyroid hyperplasia, C. MEN 1, D. Medullary carcinoma of thyroid
A: Parathyroid adenoma
Answer: A: Parathyroid adenoma 
Explanation: Primary hyperparathyroidism is a generalized disorder of calcium, phosphate, and bone metabolism due to an increased secretion of PTH. The elevation of circulating hormone usually leads to hypercalcemia and hypophosphatemia.Solitary adenomas: A single abnormal gland is a cause in ~80% of patients; the abnormality in the gland is usually a benign neoplasmor adenoma and rarely a parathyroid carcinoma.Ref: Harrison; 19th edition; Page no: 2470