Tertiary hyperparathyroidism

Secondary hyperparathyroidism (SHP) occurs in multiple disorders, most commonly renal and gastrointestinal disease, to defend against hypocalcemia and hyperphosphatemia. If such disorders are left untreated or are undertreated, chronic stimulation of parathyroid tissue may lead to parathyroid hyperplasia. Medical therapy to correct hypocalcemia or hyperphosphatemia or to directly suppress parathyroid gland growth usually corrects SHP. Occasionally, sufficient parathyroid cell mass is achieved such that even basal (i.e., suppressed) PTH production is in excess of requirements to correct hypocalcemia. Monoclonal expansion of chief cells with reduced expression of vitamin D and calcium-sensing receptors may also contribute to parathyroid autonomy and hypercalcemia that may ensue. This state, referred to as tertiary hyperparathyroidism (THP), may require surgical treatment as hypercalcemia may limit options for medical therapy. Pseudohypoparathyroidism (PHP) is an uncommon disorder characterized by resistance to PTH action leading to hypocalcemia, hyperphosphatemia, secondary elevations in PTH and, rarely, THP. In PHP, the medical and surgical approaches to THP must be carefully planned, given that normalization of PTH concentrations may not be desirable.