Pathologic calcification in dystrophic calcification occurs in dead or dying tissue despite normal serum calcium and phosphate. The initiating event at the cellular level is:

• A Elevated PTH levels directing hydroxyapatite deposition in injured tissues
• B Metastatic deposition requires elevation of calcium × phosphate product above 70 mg2/dL2
• C Macrophage-derived alkaline phosphatase raising local pH to precipitate calcium salts
• D Membrane vesicles from necrotic cells acting as nucleation sites for calcium phosphate crystal deposition ✓

Explanation

Dystrophic calcification occurs in necrotic tissues with normal serum calcium levels. The initiating event involves membrane vesicles (matrix vesicles or apoptotic vesicles) released from necrotic and dying cells that concentrate calcium via annexin-mediated transport and provide a phospholipid nucleation surface for hydroxyapatite crystal formation. Metastatic calcification is due to hypercalcemia/hyperphosphatemia and deposits in normal tissue. PTH does not direct local calcification in this mechanism.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.