Subcutaneous calcinosis: Is it different between systemic sclerosis and dermatomyositis?

Calcinosis cutis is the deposition of insoluble calcium in the skin and subcutaneous tissues. It is a manifestation of several autoimmune connective tissue diseases, most frequently with systemic sclerosis and juvenile dermatomyositis, followed by adult dermatomyositis. Autoimmune connective tissue disease-associated calcinosis is of the dystrophic subtype, which occurs at sites of damaged tissue in the setting of normal serum calcium and phosphate levels. In juvenile dermatomyositis, calcinosis is considered a marker of ongoing disease activity and possibly inadequate treatment, while in adult dermatomyositis, it is a hallmark of skin damage due to chronic rather than active disease. Calcinosis is associated with long disease duration in systemic sclerosis and dermatomyositis, anti-polymyositis/sclerosis autoantibodies in systemic sclerosis and NXP-2 and melanoma differentiation-associated gene 5 in dermatomyositis. Calcinosis in systemic sclerosis occurs most frequently in the hands, particularly the fingers, whereas in dermatomyositis, it affects mainly the trunk and extremities. The primary mineral component of calcinosis is hydroxyapatite in systemic sclerosis and carbonate apatite in dermatomyositis. Calcinosis in dermatomyositis and systemic sclerosis share some pathogenic mechanisms, but vascular hypoxia seems to play a more important role in systemic sclerosis, whereas the release of calcium from mitochondria in muscle cells damaged by myopathy may be a primary mechanism contributing to dermatomyositis-related calcinosis. Multiple treatment strategies for dermatomyositis and systemic sclerosis-related calcinosis have been used with variable results. Early aggressive treatment of underlying myositis in patients with dermatomyositis may improve long-term outcomes of calcinosis. A better understanding of the pathogenesis of calcinosis is needed to improve treatment options.