BACKGROUND: Peritoneal dialysis (PD) patients rarely develop sclerosing peritonitis (SP), a severe, life-threatening condition of unknown pathogenesis. Ossification of the peritoneum (PO) is a rare occurrence, which has, however, been reported in PD patients with SP. OBJECTIVE: To investigate etiopathogenetic correlations between PO and SP by histopathological examination. METHOD: We examined biopsy specimens, obtained by laparoscopy or during surgery from 36 patients with SP, from all parts of Italy in the past 8 years for evidence of peritoneal calcification or ossification. Other studies were performed on a sample of dense white material found under the parietal peritoneum of 1 patient during laparoscopy. RESULTS: Ossification of the peritoneum was found in 4/16 patients with calcifications. In addition to PO, we also found bone marrow in two specimens and arterial ossification in one case. In specimens with calcifications, and especially those with ossification, there was evidence of peritoneal inflammation with infiltration of lymphocytes, multinuclear giant cells, macrophages, and mast cells. The chemical composition of the whitish material was 85% calcium chloride and 15% hydroxyapatite. CONCLUSIONS: Calcifications alone were found in 33% (12/36) of cases of SP; 11% of SP cases were complicated by both peritoneal calcification and ossification (4/36), which indicates great availability of calcium under conditions of inflammation. Where does this calcium come from? In 1 patient with PO, the quantity of calcium was enormous and its unusual composition suggested a link with the calcium contained in dialysis solution.

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