The foot in acquired systemic diseases

Abstract

The deposition of calcium salts is favored by an alkaline envh'onment and is cata/yzed by the enzyme alkaline phosphatase. The formation of calciufn phosphate is a function of the product'of the concentrations of calcium and phosphate ions. When the concentration of circulating calcium in milligrams per cent multiplied by the concentration of circulating phosphate in milligrams per cent exceeds 75, the serum becomes oversaturated and metastatic or metabolic calcification occurs. =~ This situation obtains in l~ypervitaminosis D and the milk-alkali syndrome where the excess of circulating calcium and phosphate i's due to increased absorption from the gastrointestinal tract associated with impaired excretion from the kidneys. Metastatic calcification is an important feature of renal failure v,,itl~ secondary l~ypeq)arathyroidism, in which a marked elevation of serum phosphate is accompanied by ,'t nearly normal serum calcium. Figure 1 demonstrates the pattern of soft-tissue calcification characteristie of hypervitaminosis D, milk-,-dkali syndrome, and renal failure with secondary hyperparathyroidism. Calcium deposits occur in the walls of blood vessels, periarticular synovial spaces, tendon sheaths, and bursal sacs. '`'=' Streaks, beads, and bands of calcium are scattered through the subcutaneous tissue with a predileetion for extensor surfaces, such as the dorsum of the foot. Large lobulated masses may appear in the periarticular tissues, s Prominent globular deposits may also represent dystrophic calcification as a feature