<prompt> The most common cause of hyperparathyroidism isParathyroid adenomaParathyroid hyperplasiaMEN 1Medullary carcinoma of thyroid  <response>: 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 