Hypoparathyroidism is caused by insufficient or inactive parathyroid hormone secretion or, to put it simply, low PTH. There are a number of conditions in which this happens and they all have different causes.
These conditions fall into two main types of hypoparathyroidism:
1) Iatrogenic hypoparathyroidism
The most common form of hypoparathyroidism is caused by the surgical removal of, or damage to, the parathyroid glands. It is usually called post surgical or post operative hypoparathyroidism (PoSH).
(Iatrogenic means ’caused by treatment’.)
2) Idiopathic hypoparathyroidism
The more rare forms of Hypoparathyroidism are grouped together under the heading Idiopathic hypoparathyroidism. This group of rare conditions may be either congenital (occurring in the womb ) or acquired in childhood or later in life as an inherited and/or autoimmune condition. The term ‘idiopathic’ is also used to denote a form of hypopara of unknown cause.
a) Post Surgical
This is the most common cause of hypoparathyroidism in adulthood although it is still a rare condition. Permanent hypoparathyroidism occurs in around 7-10% of all neck operations. The British Association of Endocrine & Thyroid Surgeons (BAETS) say that about 30% of those who have thyroid operations will experience temporary symptoms of low calcium and may require treatment. If treatment is still ongoing after 6 months it is known as ‘late hypocalcaemia’ or hypoparathyroidism and may be permanent, requiring lifelong medication. Late hypocalcaemia after total thyroidectomy is the commonest reported complication. The overall incidence is about 9%.*
Hypoparathyroidism can occur following any surgery to the neck (thyroid, parathyroid, laryngeal or oesophogeal) where the parathyroids have been accidentally or intentionally removed or damaged and have lost their blood supply. For example, during surgery on the thyroid gland, the parathyroid glands may be accidentally damaged or removed.
The parathyroid glands may also be intentionally removed if cancerous (although this is extremely rare) or as treatment for hyperparathyroidism when parathyroid glands are overactive.
Post surgical hypoparathyroidism may be a temporary situation – if there is sufficient undamaged parathyroid tissue left or when the remaining tissue is no longer suppressed, the parathyroid glands will recover, usually within 6 months to a year. If parathyroid hormone levels remain above 18ng/L then there is a good chance that patients will eventually be able to come off their medication. If this is not the case, permanent hypoparathyroidism results.
b) Radiation or drug treatment
Hypopara can be caused by treatment for thyroid and other cancers eg radioactive iodine thyroid ablation or external beam radiation to neck or use of chemotherapy drugs. It can also occur from cancer of the parathyroid glands, HIV and AIDS.
c) Hungry bone syndrome
This is a temporary situation which can sometimes develop after a parathyroidectomy for primary hyperparathyroidism. In this case, the body has been used to high levels of calcium which has been taken from the bones into the blood. When the parathyroid gland or glands are removed, the PTH level in the blood drops suddenly and the patient becomes temporarily hypoparathyroid. The bone, which has been starved of calcium, now grabs it back and blood calcium level falls suddenly. This requires postoperative treatment with calcium for up to several days until the hypoparathyroid state resolves, and calcium levels are stabilised.