Calcifying uremic arteriolopathy (or uremic calciphylaxis) is a rare disease (prevalence \<1% of dialysis patients), but the prognosis is often catastrophic. The main non-modifiable risk factors are age, female gender, diabetes, obesity and length of time on dialysis. Today, there is no specific treatment for this pathology, and the therapeutic management is poorly codified. However, it is commonly accepted that the treatment is based on the control of risk factors, local care, and the possible addition of treatment with sodium thiosulfate. Hyperbaric oxygen therapy has also been proposed by some authors, but remains not very accessible in practice. Recently, it has been proposed to use Rheopheresis as an adjuvant treatment for severe forms of uraemic calciphylaxis. It is a technique of apheresis in double filtration, allowing the extraction of molecules of high molecular weight, and thus the improvement of the rheological conditions of microcirculation. The expected effect is the improvement of tissue oxygenation and the acceleration of the healing of skin lesions, with the consequent reduction of infectious complications. The aim of this study is to propose a large national retrospective study, studying the evolution of patients with uremic calciphylaxis and treated by rheopheresis, compared to a control group. This will allow to have a more precise idea of the contribution of Rheopheresis in this indication.