Thursday, 23 July 2009

What is the commonest cause of primary hyperparathyroidism?

Primary hyperthyroidism is due to pathologically excessive and autonomous secretion of PTH by the parathyroid glands. The key concept is that the excess secretion is autonomous - it doesn't care what the serum calcium levels are, and consequently the serum calcium ends up getting rather high. (Contrast this with secondary hyperparathyroidism, where the increased PTH secretion is appropriate in the context of a low serum calcium.)

Theoretically, excess parathyroid hormone could come from a place outside of the parathyroid glands (for instance, ectopic secretion by a tumour), but in practice this fundamentally never occurs. This is helpful, as it narrows our search down to one or more of these glands, which sit embedded in the much larger thyroid gland. There, the possibilities are:
  • an adenoma (a benign neoplasm)
  • a carcinoma (a malignant neoplasm)
  • diffuse hyperplasia (a general, non-neoplastic increase in the size of all four glands)
And the winner is...

A parathyroid adenoma, which accounts of about 85% of all cases. Congratulations to it!

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