Secondary Hyperparathyroidism

• Secondary hyperparathyroidism:
  • Is overproduction of parathyroid hormone (PTH):
    • Due to a nonparathyroid cause:
      • Usually a result of renal failure
  • Renal failure decreases the production of 1,25(OH)2 D3:
    • Impairing intestinal absorption of calcium:
      • Leading to hypocalcemia:
        • Which increases PTH secretion by the parathyroid glands:
          • Leading to diffuse or nodular hyperplasia
  • Hyperphosphatemia:
    • From decreased renal excretion also contributes to PTH secretion:
      • The resulting calcium level is low or normal
  • Less common causes of secondary hyperparathyroidism include:
    • Osteomalacia
    • Long-term lithium therapy
    • Vitamin D deficiency
    • Malabsorption syndromes
    • Secondary hyperparathyroidism has beenv increasingly described following bariatric surgery:
      • Most commonly Roux-en-Y gastric bypass and duodenal switch:
        • Due to prolonged vitamin D deficiency:
          • It occurs despite vitamin D replacement
• The pathophysiology of secondary hyperparathyroidism:
  • Is multifactorial and can result from:
    • Phosphorous retention
    • Altered vitamin D metabolism and resistance
    • Altered metabolism of PTH
    • Impaired calcemic response to PTH
    • Possible genetic mutations
• The condition most commonly occurs in patients:
  • With a history of chronic renal failure
• Gastric bypass:
  • Has also been an increasingly recognized cause of altered vitamin D metabolism
• Patients will commonly have:
  • An elevated PTH level and normal or low serum calcium:
    • In such a setting, vitamin D levels should be measured:
      • If low, treated for a minimum of 6 weeks with supplemental vitamin D
• Secondary hyperparathyroidism:
  • Is most commonly managed medically with the use of:
    • Calcimimetic agents:
      • For example cinacalcet
    • Phosphate binders
    • Adequate calcium intake
    • Vitamin D replacement
• Cinacalcet:
  • Works by binding the calcium-sensing receptors on the chief cells of the parathyroid gland:
    • Increasing its sensitivity to extracellular calcium
• Surgical treatment is indicated in patients with:
  • Renal osteodystrophy
  • Calciphylaxis:
    • Calciphylaxis is a rare complication of secondary hyperparathyroidism resulting in acute deposition of calcium in tissues and skin necrosis:
      • That may lead to a systemic inflammatory response:
        • It is associated with a high rate of mortality (87 to 93%)
    • Calcium phosphate product of ≥ 70
    • Soft tissue calcium deposition and tumoral calcinosis
    • Calcium level greater than 11 mg/dL with an inappropriately high level of PTH
• Renal osteodystrophy:
  • Is a major issue in hemodialysis patients:
    • The aluminum present in the dialysate bath:
      • Accumulates in the bone:
        • Contributes to the development of osteomalacia
• Osteitis fibrosa cystica:
  • A type of renal osteodystrophy:
    • Is characterized by marrow fibrosis and increased bone turnover
  • Bone cysts, osteopenia, and decreased bone strength develop
  • To halt the progression of this disease process:
    • These patients with secondary hyperparathyroidism are treated surgically
• Calciphylaxis:
  • Is a rare vascular disorder:
    • In which calcium is deposited in the media of small- to medium-sized arteries
      • As a result, ischemic damage:
        • To the dermal and epidermal structures develops
  • The ulcerated lesions:
    • Are extremely painful and can become infected with subsequent sepsis, and eventually death
  • Patients with early signs of calciphylaxis:
    • Should undergo an urgent parathyroidectomy:
      • Although there is some evidence that aggressive management of serum calcium and parathyroid levels:
        • With cinacalcet may be beneficial
  • Care should be taken in wound care management:
    • Because aggressive debridement can lead to chronic nonhealing wounds:
      • Since wound healing is very poor in these patients
• Uremic pruritus:
  • Is characterized by severe itching:
    • That is thought to result from increased deposition of calcium salt in the dermis:
      • Without the visible lesions of calciphylaxis
  • Parathyroidectomy:
    • Seems to alleviate these symptoms and halts progression to the more serious skin and vascular complications seen with calciphylaxis

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