Calcinosis cutis is a term used to describe a group of disorders in which calcium deposits form in the skin. Virchow initially described calcinosis cutis in 1855. Calcinosis cutis is classified into 4 major types according to etiology: dystrophic, metastatic, iatrogenic, and idiopathic. A few rare types have been variably classified as dystrophic or idiopathic. These include calcinosis cutis circumscripta, calcinosis cutis universalis, tumoral calcinosis, and transplant-associated calcinosis cutis.
In all cases of calcinosis cutis, insoluble compounds of calcium are deposited within the skin due to local and/or systemic factors. These calcium salts consist primarily of hydroxyapatite crystals or amorphous calcium phosphate. The pathogenesis of calcinosis cutis is not completely understood and a variety of factors allow for different clinical scenarios to occur.
Metabolic and physical factors are pivotal in the development of most cases of calcinosis. Ectopic calcification can occur in the setting of hypercalcemia and/or hyperphosphatemia when the calcium-phosphate product exceeds 70 mg2/dL2, without preceding tissue damage. These elevated extracellular levels may result in increased intracellular levels, calcium-phosphate nucleation, and crystalline precipitation. Alternatively, damaged tissue may allow an influx of calcium ions leading to an elevated intracellular calcium level and subsequent crystalline precipitation. Tissue damage also may result in denatured proteins that preferentially bind phosphate. Calcium then reacts with bound phosphate ions leading to precipitation of calcium phosphate.
The prognosis is determined by that of any underlying disease. Calcinosis cutis alone usually is benign. Severe complications are infrequent. When present, morbidity is related to the size and location of the calcification.
Lesions may become painful, limit mobility of an adjacent joint, or compress adjacent neural structures. Ulceration and secondary infection may occur. Vascular calcification may result in ischemia and necrosis of the affected organ.