<prompt> Most common cause of primary hyperparathyroidism-IatrogenicMedullary carcinoma thyroidParathyroid adenomaParathyroid hyperplasia  <response>: Most common cause of primary hyperparathyroidism is autonomous secretion of parathyroid hormone PTH by a parathyroid adenoma. Single adenoma 90, multiple adenomas4, nodular hyperplasia5, carcinoma1. Reference : page 769 Davidsons Principles and practice of Medicine 22nd edition 