In hypoparathyroidism the parathyroid glands do not secrete enough parathyroid hormone. This results in a low blood calcium level (hypocalcaemia) where blood calcium is less than 2.25mmol/l (10 mgs/100mls). This results in a variety of symptoms.
The causes of hypoparathyroidism are:
The common cause is thyroidectomy. The reported incidence varies from 40% to 0%. The realistic figure is 3-4%.
Very rarely autoimmune processes where the glands are attacked by the body's own immune system. This can arise for example in Polyglandular Autoimmune Syndrome Type 1 (APECED), where hypoparathyroidism occurs with adrenal insufficiency, thyroid disease and diabetes mellitus type 1. This syndrome is dealt with more specifically in its own section.
It is important to realise that hypoparathyroidism is not the only cause of hypocalcaemia, as explained in the section 'What are the parathyroids? - the importance of calcium'. Other causes of hypocalcaemia include:
1. Low serum magnesium (hypomagnesaemia) - causes reduced release of parathyroid hormone from normal parathyroids. 2. Pseudohypoparathyroidism - the parathyroid hormone is normal or increased but the due to a genetic defect, tissues are insensitive to it. Calcium levels therefore remain low. 3. Low albumin - Any reason for a low serum albumin will cause low serum calcium due to the calcium particles not being carried properly in the blood, allowing them to be excreted and lost. 4. Drugs - A variety of drugs cause hypocalcaemia due to liver or kidney damage.