Dystrophic versus metastatic calcification
Calcium deposited abnormally in tissues is either dystrophic (local, in damaged tissue) or metastatic (systemic, meaning throughout the body).
Remember
Dystrophic calcification is local, in damaged tissue, with a blood calcium that is usually normal; metastatic calcification is systemic, driven by a raised blood calcium or phosphate, and affects otherwise normal tissue.
Memory aid
Dystrophic = Damaged tissue, normal calcium; Metastatic = Many sites, high calcium
Use the shared first letters to recall which type goes with damaged tissue and which with many sites.
Pathological calcification means the abnormal deposition of calcium in tissues, and it comes in two types. In the dystrophic type the tissue is the problem, and in the metastatic type the blood is the problem.
Dystrophic calcification is local. Injured cells give calcium a nidus (a starting point or scaffold) to settle on, so the change stays at the site of injury. It occurs in dead or dying tissue, atherosclerotic plaques (fatty build-ups in artery walls), some tumours and heart valves. Because the damage is confined to the tissue, serum calcium and phosphate are usually normal on blood tests.
Metastatic calcification is systemic, so it occurs throughout the body. Abnormal calcium metabolism raises the blood calcium (hypercalcaemia: too much calcium in the blood), the blood phosphate or the calcium-phosphate product (calcium multiplied by phosphate); hydroxyapatite crystals (the calcium phosphate mineral found in bone) are deposited in tissue that was previously healthy. The kidneys, lungs and gastric mucosa (the lining of the stomach) are preferred sites. Chronic kidney disease is a classic setting, because it disturbs calcium and phosphate handling.
Here the word metastatic describes calcium spread by the blood, not the spread of cancer. Metastatic calcification is usually symptomless but, in some cases, can pose a serious risk to health, so symptoms do not separate the two types.
Key facts
- Dystrophic calcification
- local deposition of calcium salts in dead, dying or damaged tissue, with usually normal serum calcium and phosphate.
- Metastatic calcification
- systemic, with hypercalcaemia or a raised blood phosphate from abnormal calcium metabolism, and hydroxyapatite deposited in many tissues.
- Typical dystrophic sites
- heart valves, atherosclerotic plaques and areas of dying tissue.
- Metastatic sites
- the kidneys, lungs and gastric mucosa are preferred sites.
- Kidney disease link
- chronic kidney disease is a classic setting for metastatic calcification, because it disturbs calcium and phosphate handling.
- Meaning of metastatic
- it describes calcium spread by the blood, not the spread of cancer.
Exam traps
- Calcification confined to injured tissue does not need a raised serum calcium: it usually develops with a normal serum calcium, and a raised calcium is the hallmark of metastatic calcification.
- Calcification that primarily affects the kidneys, lungs and gastric mucosa (the lining of the stomach) describes the metastatic type, because these are its preferred sites; dystrophic calcification occurs wherever tissue is dead or damaged.
- Metastatic calcification can occur with a normal serum calcium when serum phosphate is raised, but it deposits in otherwise healthy tissue, so calcification within necrotic tissue is still dystrophic.
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