Subperiosteal resorption, a characteristic feature of hyperparathyroidism

why subperiosteal resorption happens on radial side in hyperparathyroidism?

Subperiosteal resorption, a characteristic feature of hyperparathyroidism, is the excessive breakdown and resorption of bone tissue on the periosteal (outer) surface of bones. In hyperparathyroidism, this phenomenon commonly occurs on the radial aspect of the phalanges (fingers) and other bones. Here’s why subperiosteal resorption tends to happen on the radial side:

  1. Vascular Distribution:
  • The periosteum is a connective tissue membrane that covers the outer surface of bones. It is highly vascularized, meaning it has an abundant blood supply. In hyperparathyroidism, elevated levels of parathyroid hormone (PTH) stimulate bone resorption.
  1. Bone Resorption Stimulation:
  • PTH directly activates osteoclasts, which are cells responsible for breaking down bone tissue. In hyperparathyroidism, the increased levels of PTH lead to increased osteoclastic activity and bone resorption.
  1. Pressure on Periosteum:
  • The radial aspect of the phalanges, being closer to the surface and having less surrounding soft tissue, is more susceptible to pressure effects. In individuals with hyperparathyroidism, the resorption of bone on the radial side may be accentuated due to increased pressure or mechanical stress on the periosteum.
  1. Distribution of Osteoclasts:
  • Osteoclasts, the bone-resorbing cells, may be more abundant or active on the radial side of bones. The specific distribution and activity of osteoclasts can vary based on the bone and individual factors.
  1. Bone Architecture:
  • The bone structure and architecture can also influence the pattern of resorption. The radial aspect of bones, particularly the phalanges, may have a particular microarchitecture that makes it more susceptible to the effects of increased osteoclastic activity.
  1. Clinical Presentation:
  • The development of subperiosteal resorption on the radial side is often observed clinically, particularly in the hands. Patients with hyperparathyroidism may present with “brown tumors” or localized bone lesions on the radial aspect of phalanges due to this resorption.

In summary, the specific distribution of subperiosteal resorption on the radial side in hyperparathyroidism is influenced by factors such as the vascularity of the periosteum, bone architecture, mechanical stress, and the action of osteoclasts under the influence of elevated PTH levels. The radial side is more prone to this resorption due to these factors, leading to characteristic bone changes seen in hyperparathyroidism.