Primary hyperparathyroidism is usually caused by a benign tumor in one or more of the parathyroid glands. In most cases, the tumor grew spontaneously. It was not due to anything that you did, and we do not have an explanation for why it occurred.

There are a few known conditions that will cause primary hyperparathyroidism, though these only apply to a small number of patients. Here are the known causes: * MEN (multiple endocrine neoplasia) syndromes 1 and 2a: These are rare genetic syndromes that commonly cause primary hyperparathyroidism through hyperplasia (enlargement of all four parathyroid glands). MEN1 is also associated with pituitary and pancreatic endocrine tumors, while MEN2a is also associated with medullary thyroid cancer and pheochromocytoma (an adrenal tumor). Most patients with MEN will have other family members with it. * Lithium: Long-term lithium usage can cause problems with calcium and the parathyroids. This does not appear to happen with short-term use, so if you were only on lithium for 2 months for example, it is unrelated. People who have been on lithium for many years are at risk of having multiple parathyroid tumors or hyperplasia (all four glands involved). * Familial primary hyperparathyroidism: Sometimes primary hyperparathyroidism just runs in families. Patients tend to get it at a younger age than in spontaneous cases, and are more likely to have multiple parathyroids involved.

Primary hyperparathyroidism can also be caused by cancer, a malignant tumor in the parathyroids, but this is exceedingly rare - so rare that you do not need to worry about it if you have just been diagnosed with parathyroid disease.