Calciphylaxis : Population, Risk Factors, Diagnostic Practice, Therapeutic and Outcome

Inclusion Criteria: * patients ≥ 18 years with chronic renal failure with Glomerular Filtration Rate \< 30ml/min/1,73m² * diagnosis of calciphylaxis between 2006 and 2016 * living in the Regions of Bretagne, Pays de la Loire, Poitou-Charentes or Centre Val de Loire. Exclusion Criteria: * realized biopsy in favor of differential diagnosis * significant arterial lesion of lesion area or differential diagnosis more valid * if the diagnosis is not based on the following criteria: 3 clinical criteria or 2 clinical criteria and biopsy in favor, criteria which are : * Patient in chronic hemodialysis or stade 4 chronic kidney disease * At least 2 painful sores and hardly curable with concomitant painful purpura * Sore and purpura localisation in trunk, extremities and penis.