Phosphate Metabolism and Pathophysiology in Parathyroid Disorders and Endocrine Tumors

Abstract

The advent of new insights into phosphate metabolism must urge the endocrinologist to rethink the pathophysiology of widespread disorders, such as primary hyperparathyroidism, and also of rarer endocrine metabolic bone diseases, such as hypoparathyroidism and tumor-induced hypophosphatemia. These rare diseases of mineral metabolism have been and will be a precious source of new information about phosphate and other minerals in the coming years. The parathyroid glands, the kidneys, and the intestine are the main organs affecting phosphate levels in the blood and urine. Parathyroid disorders, renal tubule defects, or phosphatonin-producing tumors might be unveiled from alterations of such a simple and inexpensive mineral as serum phosphate. This review will present all these disorders from a ‘phosphate perspective’.

Secondary hyperparathyroidism: Update

“…Secondary hyperparathyroidism with normal renal function is generally associated with low serum phosphate levels due to the inhibitory effect of PTH on sodium-phosphate cotransporters in renal tubules. However, this situation is not similar in patients with chronic kidney disease since, in addition to the decreased excretion of phosphate due to reduced glomerular filtration, there is also a resistance to the phosphaturic effect of FGF23 due to decreased αKlotho expression at the tubular level [27].…”

Phosphaturic Mesenchymal Tumors with or without Phosphate Metabolism Derangements

“…On suspicion of PMT, the clinician should bear in mind that 80% of filtered phosphate is reabsorbed in the proximal tubule and that when hypophosphatemia is diagnosed, a 24 h urinary phosphate >100 mg can be used to suspect renal leak of phosphate. A recent review summarizes the diagnostic algorithm of hypophosphatemia and when to consider TIO based on laboratory parameters [ 14 ]. Briefly, two calculations can be easily made to figure out if phosphate is lost through the kidneys.…”