Primary hyperparathyroidism

Etiology

• Parathyroid gland adenoma (∼ 85%): benign tumor of the parathyroid glands

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Clinical features

Symptomatic patients often have clinical features of hypercalcemia

Clinical features

• Nephrolithiasis, nephrocalcinosis (calcium oxalate > calcium phosphate stones)
• Bone pain, arthralgias, myalgias, fractures
  • Because most of the calcium is released from bones
• Constipation
  • Increase in extracellular Ca²⁺ → membrane potential outside is more positive → more amount of depolarization is needed to initiate action potential → decreased excitability of muscle and nerve tissue
• Abdominal pain
• Nausea and vomiting
• Anorexia
• Peptic ulcer disease
  • hypercalcemia-induced increase of gastric acid secretion and gastrin levels.
• Neuropsychiatric symptoms such as anxiety, depression, fatigue, and cognitive dysfunction
• Diminished muscle excitability
  • Cardiac arrhythmias
    • ECG: Shorten QT interval, see ECGs > QT interval
  • Muscle weakness, paresis
• Polyuria and dehydration
  • Due to acquired renal ADH resistance. Although ADH is being secreted, the kidneys no longer respond to it adequately (nephrogenic diabetes insipidus).

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Diagnostics

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X-ray

• Decreased bone mineral density
• Cortical thinning: especially prominent in the phalanges of the hand; manifests as acroosteolysis (a subperiosteal pattern of bone resorption)
  • Unlike the typical osteoporosis of aging, which predominantly affects trabecular bone
• Salt and pepper skull: granular decalcification manifesting as diffusely distributed lytic foci on imaging of the calvarium
• Features of osteitis fibrosa cystica

Complications

Osteitis fibrosa cystica (OFC)

• A rare skeletal disorder seen in advanced hyperparathyroidism characterized by replacement of calcified bone with fibrous tissue
• Most commonly seen in primary hyperparathyroidism but can also occur in secondary hyperparathyroidism
• ↑ PTH → ↑ RANK ligand expression → activation of osteoclasts → bone resorption, cortical bone destruction, and fibrous tissue deposition
• Features include bone pain, subperiosteal thinning, and bone cysts; multiple bone cysts in the skull may result in a salt and pepper skull (pepper pot) appearance on x-ray.
• In advanced OFC, large, cystic, vascular cavities with a tumor-like appearance on x-ray and a brown color due to hemosiderin deposition (brown tumors) can form in long bones.