Teaching Pearls:

• Primary hyperparathyroidism and malignancy comprise of >90% of cases of hypercalcemia.
• Primary hyperparathyroidism is the most common cause of hypercalcemia in outpatient settings.
  • Patients are often asymptomatic and/or have a history of kidney stones
• Malignancy is the most common cause of hypercalcemia in inpatient admissions.
  • Labs often display severe hypercalcemia
  • Patients with severe hypercalcemia are often volume depleted as hypercalcemia can lead to nephrogenic diabetes insipidus
• Initial Workup – First measure the PTH level
  • High PTH: diagnosis is likely primary hyperparathyroidism
  • High normal to mild elevation: think of primary hyperparathyroidism or Familial hypocalciuric hypercalcemia (FHH)
  • Low PTH: proceed onto further tests
• Other work-up labs include PTHrP and vitamin D metabolites. Other considerations include SPEP/UPEP, TSH, Vitamin A, etc.
• FHH differs from primary hyperparathyroidism in that the fractional excretion of Ca in FHH is low, whereas primary hyperparathyroidism is high.
  • Decreased fractional excretion of Calcium leads to lack of nephrolithiasis development.
• Primary hyperparathyroidism has three different pathologic conditions:
  • Adenoma – 89-90%
  • Hyperplasia – 6.8%
  • Carcinoma – 1.2%
• Should consider parathyroid carcinoma in patients with primary hyperparathyroidism and the following:
  • Severe elevations in calcium
  • Severe elevations in PTH
• Management
  • IV fluids NS at 200-300cc/hour to maintain UO at 100-150cc/hour.
    • Loop diuretics only used in the setting of fluid overload
  • Calcitonin – onset of action: hours
    • Concern for tachyphylaxis
  • Bisphosphonates (pamidronate or zolendronate)
    • Onset of action >2 days