Hyperparathyroidism

Hyperparathyroidism is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

A dysfunction of the body’s normal regulatory feedback mechanisms resulting in excess production of parathyroid hormone (PTH)

  • Primary hyperparathyroidism (HPT): intrinsic parathyroid gland dysfunction resulting in excessive secretion of PTH with a lack of response to feedback inhibition by elevated calcium
  • Secondary HPT: excessive secretion of PTH in response to hypocalcemia, which can be caused by vitamin D deficiency or renal failure
  • Tertiary HPT: autonomous hyperfunction of the parathyroid gland in the setting of long-standing secondary HPT

Epidemiology

Incidence
  • Predominantly postmenopausal females
  • Female > male (3:1)

Prevalence
Primary HPT is 1 in 500 to 1 in 1,000 in the United States

Etiology and Pathophysiology

  • PTH is synthesized by the four parathyroid glands, which are located behind the four poles of the thyroid gland (locations can vary).
  • Ectopic (abnormal locations and most common is the thymus) or supernumerary glands (more than four glands)
  • PTH releases calcium from bone by osteoclastic stimulation (increasing bone resorption).
  • PTH increases reabsorption of calcium in the distal tubules of the kidneys.
  • PTH stimulates conversion of 25-hydroxycholecalciferol (25[OH]-Vit D) to 1,25-dihydroxycholecalciferol (1,25[OH]2-Vit D or active vitamin D) in the kidneys. 1,25(OH)2-Vit D increases calcium and phosphate absorption from the GI tract and kidneys, and stimulates osteoclastic activity and bone resorption.
  • Primary HPT: unregulated PTH production and release due to the loss of normal feedback control by extracellular calcium, causing increase in serum calcium
    • Solitary adenoma (80–85%)
    • Diffuse hyperplasia (10–15%) of the four parathyroid glands, either sporadically or in association with multiple endocrine neoplasia (MEN) types I or II
    • Parathyroid carcinoma (<1%), a very rare and severe form
  • Secondary HPT: adaptive parathyroid gland hyperplasia and hyperfunction
    • Dietary: vitamin D or calcium deficiency
    • Chronic renal disease resulting in the following:
      • Renal parenchymal loss causing hyperphosphatemia
      • Impaired calcitriol production causing hypocalcemia
      • General skeletal and renal resistance to PTH
  • Tertiary HPT: autonomous oversecretion of PTH following prolonged parathyroid stimulation

Genetics
  • MEN types I and II: Patients with multiple gland hyperplasia in the absence of renal disease should be screened for MEN-I gene mutation.
  • Neonatal severe primary HPT
  • HPT—jaw tumor syndrome
  • Familial hypocalciuric hypercalcemia (FHH)
  • Familial isolated HPT

Risk Factors

Chronic kidney disease, increasing age, poor nutrition, radiation, and/or family history

General Prevention

Adequate intake of calcium and vitamin D may help prevent secondary HPT.

Commonly Associated Conditions

  • Vitamin D deficiency
  • Chronic renal failure
  • MEN syndromes types I and II

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Citation

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TY - ELEC T1 - Hyperparathyroidism ID - 117547 ED - Baldor,Robert A, ED - Domino,Frank J, ED - Golding,Jeremy, ED - Stephens,Mark B, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/117547/all/Hyperparathyroidism PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -