Osteopontin expression in biopsies of calciphylaxis.

BACKGROUND: Calciphylaxis combines features of vascular thrombotic occlusion and endoluminal calcification. In this study we examine the expression of osteopontin as a diagnostic marker and its role in lesional pathogenesis.

METHODS: 25 formalin-fixed, paraffin embedded skin biopsies of 20 females and 5 males (mean age of 60 years) with a diagnosis of calciphylaxis were assessed for osteopontin expression.

RESULTS: Lower extremities were the most commonly involved areas; however a truncal and genital distribution was also noted in 3 cases. Renal failure was present in 21 of 25 cases. One patient had myeloproliferative disorder and one patient had advanced colon cancer. The dominant pathology was localized to the subcutaneous fat, characterized by mural calcification and luminal thrombosis affecting capillaries, venules, arterioles and small arteries. In 2 cases, a subcutaneous thrombogenic vasculopathy without calcification was noted. Osteopontin expression was confined to the subcutis, being most striking in calcified vessels but also apparent in vessels without calcification, including mineral poor variants of calciphylaxis.

CONCLUSION: Calciphylaxis represents a unique calcific thrombogenic vasculopathy, not limited to renal failure. Ectopic osteopontin expression may define a critical and initial event in the calciphylaxis pathogenesis. Therapeutic agents designed to reduce osteopontin expression may be of value in its treatment.