The parathyroid glands should release parathyroid hormone in response to low or falling calcium. Parathyroid hormone (PTH) causes increased calcium and decreased phosphate.
Primary hyperparathyroidism
Primary hyperparathyroidism is the inappropriate secretion of PTH, resulting in hypercalcaemia.
Presentation was classically with the signs/symptoms of hypercalcaemia (‘bones, stones, abdominal groans and psychic moans’) but now 80% of cases are detected incidentally on bloods.
Biochemically there is a raised serum calcium, elevated or inappropriately normal PTH and often a low serum phosphate due to renal phosphate wasting.
85% of cases are caused by a single adenoma.
Parathyroid carcinoma is rare, affecting <0.5% of those with hyperparathyroidism.
Primary hyperparathyroidism may be hereditary – it is a feature of MEN I and MEN IIa.
Treatment
- Parathyroidectomy
- if calcium > 1.0mg/dl above upper limit of normal or creatinine clearance <60ml/min or osteoporosis or aged under 50
- 95% cure
- small risk of recurrent laryngeal nerve palsy
- risk of 'hungry bone syndrome' - associated with hypocalcemia, hypophosphatemia, and low urinary calcium excretion
- Medical management
- Adequate hydration
- Avoid immobility
- Alendronate to increase bone mineral density
NB it is important to differentiate primary hyperparathyroidism from familial hypocalciuric hypercalcaemia as the latter does not require any treatment.
Secondary hyperparathyroidism
Secondary hyperparathyroidism is characterised by raised PTH with low calcium - it is therefore an appropriate homeostatic response.
The commonest causes of secondary hyperparathyroidism are chronic renal failure and vitamin D deficiency.
Tertiary hyperparathyroidism
Tertiary hyperparathyroidism is seen after long-term secondary hyperparathyroidism due to hyperplasia of the parathyroid glands. It results in raised calcium and very raised PTH. It generally occurs in end stage renal failure.
Summary
Small print gem: Hyperparathyroidism-jaw tumour syndrome is a rare condition in which there is a solitary parathyroid adenoma with associated bone lesion in the jaw and either Wilms’ tumour or renal cysts.
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