In this study, we showed that the PMT and peritoneal permeability, represented by D/P Cr, were significantly correlated, and PMT was not necessarily increased with an increase in PD duration. To our knowledge, this study is the largest study evaluating the peritoneum by sonography and is the first study in which the PMT was repeatedly measured over time during PD treatment.
Duman et al. measured the PMT of 42 PD patients who had undergone PD for > 12 months using sonography and showed, for the first time, that the PMT was positively correlated with D/P Cr . Subsequently, the correlation between PMT and peritoneal permeability has been reported in several studies using sonography [11–13]. Honda et al. showed in their study, which evaluated peritoneal specimens of 253 patients before and during PD treatment, that the PMT increased and the lumen/vessel diameter ratio, which was reported as an indicator of vasculopathy in their study, decreased with an increase in PD duration . They also showed that the PMT was significantly higher in patients with ultrafiltration failure than in patients with a preserved ultrafiltration capacity. Plum et al. showed that patients characterized as being high transporters, according to the peritoneal equilibration test, had an increased submesothelial fibrous layer thickness . Based on these pathological studies, PMT may reflect vasculopathy or fibrosis of the peritoneum.
Conversely, bPMT tended to correlate with BMI and the presence of DM, but not with D/P Cr in this study. A previous morphological study evaluating the peritoneum of PD patients with or without DM at the start of PD showed that the submesothelial connective tissue thickness and the number of capillaries were significantly greater in the DM group than in the non-DM group . However, to date, there have been no studies evaluating the correlation between PMT and peritoneal permeability at the start of PD using either peritoneal specimens or sonography.
There were no significant differences between bPMT and lPMT in all patients. These measures were not significantly different even among patients who discontinued PD due to peritoneal dysfunction. Moreover, the annual PMT, measured for 3 years prior to PD withdrawal, was preserved, contrary to our hypothesis that the PMT would be higher in patients who had discontinued PD due to peritoneal dysfunction. Inconsistent with the findings of our study, several previous studies have shown that PMT increased with a longer PD duration [8, 10, 12–14]; however, these studies had cross-sectional study designs. Williams et al. evaluated the peritoneal biopsy specimens of 130 PD patients and showed that the thickness of the submesothelial compact zone increased significantly with an increase in PD duration . However, these findings were not observed in patients without PD-related problems or membrane failure. Similarly, Lee et al. showed, based on sonographic examination, that the PMT was not associated with PD duration .
In Japan, since around 2005, most PD patients have used a pH-neutral, low-glucose degradation product (GDP) dialysate, which is more biocompatible than conventional dialysates. Since then, several studies have shown that a pH-neutral low-GDP dialysate might prevent morphological and functional changes in the peritoneum [15, 18–20]. Tawada et al. compared the peritoneal biopsy samples of 54 PD patients treated with a conventional acidic dialysate to those of 73 PD patients treated with a pH-neutral low-GDP dialysate . They showed that the PMT was higher and the lumen/vessel diameter ratio was smaller in the conventional dialysate group than in the pH-neutral dialysate group and that the lumen/vessel diameter ratio negatively correlated with PD duration and D/P Cr in the conventional dialysate group but not in the pH-neutral dialysate group. From these findings, they suggested that a pH-neutral low-GDP dialysate might prevent morphological and functional changes in the peritoneum. Among the 115 patients in this study, only seven patients started PD therapy before 2005, and most patients were treated with a pH-neutral dialysate from the onset of treatment. Based on these facts, one of the reasons as to why the PMT was not correlated with PD duration in this study might possibly be explained by the use of a biocompatible dialysate.
Several studies showed that inhibition of the renin-angiotensin-aldosterone system (RAAS) prevented the morphological deterioration of the peritoneum in animal models [21, 22]; although, the effectiveness of RAAS inhibitors in protecting the peritoneal membrane function of PD patients has remained unclear . In this study, a greater percentage of patients were taking RAAS inhibitors than that reported in a previous study , and this may have contributed to the preservation of the peritoneal membrane.
In this study, we were unable to identify factors related to the PMT change rate. The bPMT was higher in the group with a decreased PMT over time than in the group with an increased PMT over time. This might be partly explained by the percentage of patients with DM in both groups. We found that the complications of DM tended to correlate with the bPMT. Of those with a decreased PMT over time, 45.5% had DM, whereas 25.0% of patients in the group with an increased PMT over time had DM. However, this difference was not significantly different.
There were some limitations to this study. First, this study was a retrospective single-center study. Therefore, selection bias could not be completely eliminated. Second, the timing of the lPMT during PD treatment varied depending on the patients, because sonographic examinations were not necessarily conducted every year. However, we evaluated the annual change in PMT for 3 years before PD withdrawal and found that the PMT was preserved over time. Third, the concentration of glucose in the dialysate was not adjusted for statistically, because detailed PD prescription data were not compiled in this study. However, the use of a dialysate containing more than 2.5% glucose was not correlated with lPMT or the PMT change rate in the univariate analysis.