Tertiary hyperparathyroidism is-: (A) High PO
4
 level with metastasis, (B) Secondary hyperparathyroidism with CRF, (C) Primary hyperparathyroidism with low Cam' levels, (D) Secondary hyperparathyroidism with chief cell adenoma
Answer is D. Davidson states "In very small proportion of cases of secondary hyperparathyroidism continuous stimulation of the parathyroid may result in adenoma formation and autonomous PTH secretion. This is known as tertiary ​hyperparathyroidism".