TRANSFORMED MESOTHELIAL CELLS IN PATIENTS ON CAPD FOR MEDIUM-TERM TO LONG-TERM PERIODS

Objective: To describe the characteristics of abnormal cells present i n the peritoneal effluent of 4 continuous ambulatory peritoneal dialys is (CAPD) patients; the cells were accidentally detected in a longitud inal study of cell populations in 83 patients. Design: Descriptive stu dy. Participants: Four stable CAPD patients (2 male, 2 female). Interv entions: Peritoneal cells were collected from nocturnal peritoneal eff luent (NPE) by centrifugation. Measurements: Light microscopy, ultrast ructural, cytochemical, and immunohistochemical characteristics were s tudied. Results: The abnormal cells were characterized by a flat appea rance, large size (diameter 100 pm) - six to ten times larger than a n ormal macrophage, a broad acidophilic cytoplasm with rare granulations , and a low nucleus/cytoplasm ratio. The nucleus was pyknotic, with de nse chromatin and sometimes appeared fragmented. Its number presented a considerable variability between the patients and was much higher in the 2 females. This number remained stable in each patient over time. These cells were negative for beta-glucuronidase and positive for PAS stain with variable intensity. A very low number of flat cells were p ositive for vimentin with weak intensity, whereas cytokeratin and epit helial membrane antigen (EMA) were positive in a higher number of cell s with medium to strong intensity. Ultrastructural studies showed nume rous short surface microvilli, cytoplasm well-developed with intracyto plasmic lumina and abundant, dispersed intermediate filaments, scatter ed mitochondria, and stacks of rough endoplasmic reticulum were observ ed. Dispersed secretory vacuoles and isolated lipid vacuoles were pres ent. Conclusion: All these features imply that they are mesothelial in origin and are suggestive of a change known as peritoneal squamous me taplasia. To date, the clinical follow-up of our patients has shown a benign outcome; further studies are necessary to elucidate the signifi cance of this peritoneal squamous metaplasia in CAPD patients.