Metastatic calcification and dystrophic calcification are pathological calcification which means abnormal calcium deposits at the places where these are normally not found.
Heterotopic ossification is another name for pathologic calcification and both metastatic and dystrophic calcification constitute heterotopic calcification.
Normally, inorganic calcium salts are found in bones and teeth.
Pathologic or heterotopic calcification is the deposition of calcium salts in tissue other than osteoid [bone] and enamel [teeth]
Here are the details of these types of calcification
In this type of calcification, the tissue being affected is normal but the main defect is an elevated blood calcium level. Elevated calcium causes deposition of the calcium in tissues and results in the removal of calcium from the bones.
This type of calcium deposition occurs in a variety of sites like kidneys, lungs, stomach, blood vessels, cornea.
Causes of Metastatic Calcification
- Chronic Renal Failure [causes secondary hyperparathryoidism]
- Excessive absorption of calcium from the bowel
- Hypervitaminosis D
- Idiopathic hypercalcemia of infancy
- Parathyroid adenoma [causes primary hyperparathyroidism]
- Multiple myeloma
- Hypopharyngeal squamous cell carcinoma
- Synovial sarcoma
- Breast carcinoma
- Destructive bone lesions
- Renal tubular acidosis
- Mechanism of metastatic calcification
The mechanism of metastatic calcification is not clear.
Metastatic calcification can be influenced by the release of excess calcium salts from the bone. Phosphate concentration, alkaline phosphatase activity, and alkaline environment may contribute.
This leads to precipitation of The calcium phosphate and calcium carbonate salts in tissues.
Metastatic calcification occurs when there is hypercalcemia but it doesn’t happen in all cases of hypercalcemia.
In dystrophic calcification, serum calcium levels are normal and the calcium salts are deposited in dead or degenerate tissues.
Mechanism of Dystrophic Calcification
The process of dystrophic calcification starts in membrane-bound vesicles within cells. When the membrane gets damaged, calcium binds to the phospholipid in the membrane. Phosphatases within the membrane add phosphate groups to the calcium, forming calcium phosphate which is the hydroxyapatite crystals in the regular bone.
Examples of Dystrophic Calcification
Following are examples of dystrophic calcification
- Calcification of caseous tissue in tuberculosis
- After fat necrosis in the breast or pancreatitis
- Calcification in thrombus such as left ventricular thrombus, coronary artery calcification, inferior vena cava, superior vena cava
- Hemorrhagic infarction in the spleen
- Calcified hematoma
- Myositis ossificans
- Atherosclerotic plaques
- Granulation tissue in chronic inflammation like constrictive pericarditis
- Monckeberg’s sclerosis – A form of arteriosclerosis
- Infection as in Schistosomiasis [Leads to calcification of the ureters, bladder, and seminal vesicles
- Degenerate colloid goiter
- Calcification in various types of cyst
- Calcinosis Cutis
- Degenerate tumor-like uterine leiomyoma