The parathyroid glands produce a chemical called parathyroid hormone (PTH), which controls the level of calcium in the blood. Calcium is quite important for nerve and muscle function and consequently is quite tightly controlled in the body.
The parathyroid glands can become overactive (hyperparthyroidism) when the excess levels of PTH cause the levels of calcium to go up and this can be detected on routine blood tests. This is called primary hyperparathyroidism.
The commonest cause is an overactive gland due to a small tumour called a parathyroid adenoma. There are normally four parathyroid glands, any of which or several of which can become overactive. These glands are small, about the size of a large grain of rice and lie behind and related to the thyroid gland normally, but their position can be very variable.
Symptoms are very varied and tend to be vague. The strongest associations are with kidney stone disease, bone pain and thinning, heart rate defects and heart disease, together with weakness, tiredness and mental difficulties.
Proving the diagnosis involves blood tests, and is followed by localisation: trying to find where the overactive gland is.
The treatment is surgical removal of the gland(s).