Metastatic calcification and its organ manifestation

1. Definition

• Deposition of Ca²⁺ salts in otherwise normal tissue due to hypercalcemia (elevated serum Ca²⁺).
• Contrast dystrophic calcification (damaged tissue, normal serum Ca²⁺).
• Caused by altered metabolism, ↑Ca²⁺ absorption, or ↓excretion.

2. Sites & Morphology

• Deposits where pH is relatively alkaline favors precipitation: lungs, stomach (gastric mucosa), kidneys (also systemic arteries, pulmonary veins).
• Usually asymptomatic; severe → respiratory dysfunction, nephrocalcinosis.
• Histology resembles dystrophic deposits (basophilic, granular; von Kossa positive).

3. Causes of Hypercalcemia

• Hyperparathyroidism: ↑PTH (adenoma/carcinoma) → ↑intestinal Ca²⁺ absorption.
• Bone destruction: Ca²⁺ released — multiple myeloma, Paget disease, metastatic breast cancer.
• Vitamin D–related disorders (excess, sarcoidosis).
• Chronic renal failure → secondary hyperparathyroidism:
  • Failing kidney can’t excrete phosphate → ↑serum PO₄³⁻.
  • Ca²⁺ and PO₄³⁻ are inversely related (↑PO₄ → ↓Ca²⁺) → hypocalcemia → ↑PTH → Ca²⁺ mobilization → metastatic calcification.

💡 High-yield: Metastatic calcification = normal tissue + hypercalcemia. Top causes: hyperparathyroidism, bone-destroying malignancy, vitamin D excess, and CKD → secondary hyperparathyroidism. Favored sites are relatively alkaline: lung, stomach, kidney.