What is tertiary hyperparathyroidism?

Five patients who had gross abnormalities of calcium and phosphorus metabolism due to long standing renal failure are described to illustrate the difficulties with the term "tertiary hyperparathyroidism". One patient who had unequivocal biochemical tertiary hyperparathyroidism was found histologically to have nodular hyperplasia of all four glands even though one gland weighed twice as much (12g) as the combined weight of the other three. Another patient was not hypercalcaemic but had all the other features of the condition including rapid onset of osteitis fibrosa, vascular calcification and a probable parathyroid adenoma, with hyperplasia of the three glands. The other three had hypercalcaemia only after a reduction in the plasma inorganic phosphorus due either to renal transplantation or aluminum hydroxide therapy. The bone histology of the five patients varied from severe osteomalacia to severe osteitis fibrosa. A consideration of the factors involved in causing hypercalcaemia in these patients and a review of the literature leads to the conclusion that the term tertiary hyperparathyroidism is often misleading and best avoided.