There are three disorders affecting the parathyroids that cause spontaneous excessive secretion of parathyroid hormone. They are not amenable to long term medical treatment but respond to surgery.
The three causes are:
1. A single benign parathyroid tumour (parathyroid adenoma) - 80% of cases
2. Two or more enlarged glands (parathyroid hyperplasia) - 19% of cases
3. Parathyroid cancer - 1% of cases
The causes of such tumours are varied. Like thyroid tumours, parathyroid tumours both cancerous and non-cancerous may be induced by irradiation to the neck. In Sipple's Syndrome, multiple parathyroid tumours may co-exist with tumours of the adrenal and thyroid glands. This is part of the Multiple Endocrine Neoplasia (MEN) type 2 syndrome. Here, genetic mutations in genes such as the 'Ret' proto-oncogene predispose individuals to tumours within several endocrine glands. Parathyroid hyperplasia commonly occurs in MEN type 1 syndrome in association with pancreatic, adrenal and pituitary tumours.
Parathyroid cancer is very rare; it is often difficult to diagnose, but an indication that it exists is a very high calcium and parathyroid hormone level in the blood.