Hyperparathyroidism



There are four parathyroid glands situated in four corners of the thyroid gland. The parathyroid glands, specifically the chief cells in the glands, produce parathyroid hormone in response to hypocalcaemia (low blood calcium).

Parathyroid hormone acts to raise blood calcium level by:

  • Increasing osteoclast activity in bones (reabsorbing calcium from bones)
  • Increasing calcium absorption from the gut
  • Increasing calcium absorption from the kidneys
  • Increasing vitamin D activity

Vitamin D acts to increase calcium absorption from the intestines. Parathyroid hormone acts on vitamin D to convert it into active forms. So vitamin D and parathyroid hormone act together to raise blood calcium levels.

Symptoms of Hypercalcaemia

It is worth remembering the “renal stones, painful bones, abdominal groans and psychiatric moans”  mnemonic for the symptoms of hypercalcaemia:

  • Renal stones
  • Painful bones
  • Abdominal groans refers to symptoms of constipation, nausea and vomiting
  • Psychiatric moans refers to symptoms of fatigue, depression and psychosis

 

Primary Hyperparathyroidism

Primary hyperparathyroidism is caused by uncontrolled parathyroid hormone produced directly by a tumour of the parathyroid glands. This leads hypercalcaemia: an abnormally high level of calcium in the blood.  This is treated by surgically removing the tumour.

 

Secondary Hyperparathyroidism

This is where insufficient vitamin D or chronic renal failure leads to low absorption of calcium from the intestines, kidneys and bones. This causes hypocalcaemia: a low level of calcium in the blood.

The parathyroid glands reacts to the low serum calcium by excreting more parathyroid hormone. Over time the total number of cells in the parathyroid glands increase as they respond to the increased need to produce parathyroid hormone. This is called hyperplasia. The glands become more bulky. The serum calcium level will be low or normal but the parathyroid hormone will be high. This is treated by correcting the vitamin D deficiency or performing a renal transplant to treat renal failure.

 

Tertiary Hyperparathyroidism

This happen when secondary hyperparathyroidism continues for a long period of time. It leads to hyperplasia of the glands. The baseline level of parathyroid hormone increases dramatically. Then when the cause of the secondary hyperparathyroidism is treated the parathyroid hormone level remains inappropriately high. This high level of parathyroid hormone in the absence of the previous pathology leads to high absorption of calcium in the intestines, kidneys and bones and causes hypercalcaemia. This is treated by surgically removing part of the parathyroid tissue to return the parathyroid hormone to an appropriate level.

 

Summary

Hyperparathyroidism

Cause

PTH

Calcium

Primary

Tumour

High

High

Secondary

Low vitamin D or CKD

High

Low / Normal

Tertiary

Hyperplasia

High

High

 

Last updated December 2018
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