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Differentiate dystrophic from metastatic calcification with examples.

Pathology · 2nd Professional — Para-Clinical

Definition

Pathological calcification is the abnormal deposition of calcium salts, with smaller amounts of iron, magnesium and other minerals, within tissue.

The Two Types

Feature	Dystrophic	Metastatic
Serum calcium	Normal	Raised — hypercalcaemia
Tissue involved	Dead or dying	Normal and viable
Mechanism	Local — damaged membranes can no longer exclude calcium; phosphate-rich membrane vesicles nucleate crystals	Systemic — the calcium×phosphate product exceeds solubility
Underlying disorder	Local tissue injury	Disturbed calcium metabolism
Reversibility	No	May regress if the cause is corrected

Sites of Dystrophic Calcification

Atheromatous plaques — the commonest and most important; makes the vessel rigid and complicates surgery
Damaged heart valves — calcific aortic stenosis in a bicuspid or ageing valve; rheumatic mitral disease
Old tuberculous foci — the Ghon focus and calcified nodes, seen as healed lesions on a chest radiograph
Areas of fat necrosis in acute pancreatitis and after breast trauma
Psammoma bodies — concentric lamellated calcified structures in papillary carcinoma of the thyroid, serous papillary cystadenocarcinoma of the ovary, meningioma and mesothelioma
Dead parasites — calcified cysticerci in brain and muscle, common in India and a frequent incidental radiological finding
Monckeberg medial sclerosis; old thrombi (phleboliths); degenerating fibroids

Causes of Metastatic Calcification

Mechanism	Causes
Increased parathyroid hormone	Primary hyperparathyroidism; secondary hyperparathyroidism of chronic renal failure; PTH-related peptide from tumours
Destruction of bone	Multiple myeloma, leukaemia, bone metastases, Paget disease, prolonged immobilisation
Vitamin D disorders	Vitamin D intoxication; sarcoidosis, in which macrophages activate vitamin D
Renal failure	Phosphate retention drives secondary hyperparathyroidism
Milk-alkali syndrome	Excessive calcium with absorbable alkali

Preferred sites — tissues that lose acid and so have a relatively alkaline interstitium: gastric mucosa, kidney, lung, systemic arteries and pulmonary veins

CLINICAL PEARL

Metastatic calcification picks the tissues that excrete acid. Stomach, kidney and lung all lose hydrogen ion, so their interstitium is relatively alkaline — and calcium phosphate is far less soluble at alkaline pH. That single principle predicts the whole list of sites without memorising it.

Applied Aspects

Radiologically visible calcification is a valuable clue — popcorn calcification in a pulmonary hamartoma, laminated in a granuloma, and fine stippled microcalcification on mammography suggesting carcinoma
Nephrocalcinosis from metastatic calcification causes progressive renal impairment, and the underlying hypercalcaemia must be identified
Calcification does not mean a lesion is benign — psammoma bodies occur in frankly malignant tumours
Coronary artery calcium scoring on CT quantifies atherosclerotic burden and predicts cardiovascular risk
Calcified valves cannot be repaired and generally require replacement, so the finding alters surgical planning

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