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Correlation between Peritoneal Mesothelial Cell Cytology and Peritoneal Histopathology with Respect to Prognosis in Patients on Continuous Ambulatory Peritoneal Dialysis

Background: Sclerosing encapsulating peritonitis (SEP) is a serious complication seen in patients on long-term continuous ambulatory peritoneal dialysis (CAPD). We have previously reported that mesothelial cells in effluent dialysate significantly increased in size as the duration of CAPD progressed. In this study, we investigated the relationship between mesothelial cytology, histopathology of the peritoneum, and clinical outcomes of 34 CAPD patients. Methods: When peritoneal dialysis catheters were inserted (n = 7) or removed (n = 27), a peritoneal biopsy was performed and results compared with mesothelial cytology in effluent dialysate. Results: A significant positive correlation was noted between the duration of CAPD and the surface area of peritoneal mesothelial cells (r = 0.721, p < 0.0001). The surface area of mesothelial cells in peritoneal sclerosis (n = 9; 584 ± 97 µm2) was significantly greater than in peritoneal fibrosis (n = 14; 389 ± 26 µm2, p < 0.05), pathologic acute peritonitis (n = 3; 223 ± 10 µm2, p < 0.005), and normal peritoneum (n = 7; 247 ± 12 µm2, p < 0.001). The surface area in sclerosing peritonitis (n = 1; 1,200 µm2) was greater than that of all the others. Giant cells were found in the 1 case with sclerosing peritonitis and in 3 of 9 cases with peritoneal sclerosis, although they were found in only 1 of 14 patients with peritoneal fibrosis and in none of those with pathologic acute peritonitis or normal peritoneum. As the surface area of mesothelial cells increased to more than 400 µm2 and giant cells appeared in the effluent, the frequency of peritoneal sclerosis and/or clinical SEP increased. Conclusion: An increase in the mesothelial cell surface area and the emergence of giant cells in the effluent indicate advanced peritoneal histopathology, and may be useful indicators to determine appropriate timing of discontinuation of CAPD to prevent the development of SEP.