Why may a spontaneous fracture occur in persons with hyperparathyroidism?
Hyperparathyroidism, characterized by excessive secretion of parathyroid hormone (PTH), has long been recognized to potentially lead to the development of spontaneous fractures. This increased fracture risk is primarily attributed to the derangements in calcium and phosphate homeostasis caused by excessive PTH production.
Here's why spontaneous fractures may occur in individuals with hyperparathyroidism:
1. Loss of Bone Density:
- PTH regulates bone metabolism by promoting bone resorption (the breakdown of old bone tissue) and inhibiting bone formation.
- In hyperparathyroidism, excessive PTH levels lead to an imbalance in bone remodeling, favoring resorption over formation. This results in a net loss of bone mass and decreased bone density, making the bones weaker and more susceptible to fractures.
2. Altered Bone Microarchitecture:
- PTH affects the structural composition of bone tissue.
- It disrupts the normal arrangement of collagen and mineral components within the bone matrix, leading to the development of weaker, more brittle bone tissue.
- The changes in bone microarchitecture further increase the risk of fractures.
3. Increased Bone Fragility:
- Hyperparathyroidism causes an imbalance in the levels of calcium and phosphate in the body.
- High PTH levels promote increased urinary excretion of phosphate, resulting in hypophosphatemia (low phosphate levels).
- This combination of hypercalcemia (high calcium levels) and hypophosphatemia further compromises bone mineralization and weakens bone tissue, contributing to the risk of fractures.
4. Bone Cyst Formation:
- In some cases of severe hyperparathyroidism, the excessive PTH can lead to the formation of bone cysts or brown tumors.
- These are localized areas of bone destruction and replacement by fibrous tissue.
- Cyst formation weakens the bone structure, making it more prone to pathological fractures.
It's important to note that not all individuals with hyperparathyroidism will experience spontaneous fractures. However, the presence of this condition significantly increases the risk, making early diagnosis and appropriate management essential to prevent fractures and maintain bone health.