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!