Hyperparathyroidism

Hyperparathyroidism is a disorder characterized by excessive secretion of parathyroid hormone (PTH), leading to hypercalcemia, hypophosphatemia, and increased bone resorption. It can be primary, secondary, or tertiary.

Definition

Epidemiology

Primary hyperparathyroidism is more common in women, especially postmenopausal
Incidence: ~1–7 per 1,000 adults, higher in older populations
Secondary hyperparathyroidism occurs commonly in chronic kidney disease (CKD)
Tertiary hyperparathyroidism develops after long-standing secondary hyperparathyroidism, usually post-renal transplantation

Etiology

Primary: parathyroid adenoma (~85%), hyperplasia (~15%), carcinoma (rare)
Secondary: chronic hypocalcemia from CKD, vitamin D deficiency, malabsorption
Tertiary: autonomous PTH secretion after prolonged secondary hyperparathyroidism
Genetic syndromes: MEN1, MEN2A, familial hyperparathyroidism

Pathophysiology

Excess PTH → increased bone resorption → release of calcium and phosphate into blood
Increased renal calcium reabsorption and phosphate excretion
Increased conversion of 25(OH)D to 1,25(OH)2D in kidneys → increased intestinal calcium absorption
Hypercalcemia develops in primary hyperparathyroidism; secondary hyperparathyroidism typically maintains normocalcemia until late stages
Tertiary hyperparathyroidism leads to hypercalcemia due to autonomous PTH secretion