There are three causes of primary hyperparathyroidism. Some eighty- five per cent of patients have a single benign adenoma of one of the four parathyroid glands. Most of the remainder have hyperplasia of four parathyroid glands.
This occurs more commonly in patients with familial hyperparathyroidism syndromes, and particularly in patients with multiple endocrine neoplasia (MEN). Less than one per cent of all patients have a carcinoma of one of the four parathyroid glands. In rare cases, carcinoma seems to follow a previous adenoma.
