Background: Long-term peritoneal dialysis (PD), especially with nonphysiological solutions, is afflicted with the severe complication of encapsulating peritoneal sclerosis (EPS). Physiologic PD solutions have been introduced to reduce pH trauma. Data on peritoneal biopsies in pediatrics with long-term PD using physiological solutions are scant. Case Report: We report an adolescent who had been on 10-h continuous hourly cycles using mostly 2.27% Physioneal™ for 5 years. There were two episodes of peritonitis in October 2017 (Klebsiella oxytoca) and May 2018 (Klebsiella pneumoniae), which were treated promptly. This adolescent, who lost two kidney transplants from recurrent focal and segmental glomerulosclerosis, underwent a peritoneal membrane biopsy at the time of a third PD catheter placement, 16 months after the second renal transplant. Laparoscopically, the peritoneum appeared grossly normal, but fibrosis and abundant hemosiderin deposition were noted on histology. The thickness of the peritoneum was 200–900 (mean 680) µm; normal for age of 14 years is 297 [IQR 229, 384] μm. The peritoneum biopsy did not show specific EPS findings, as the mesothelial cells were intact, and there was a lack of fibrin exudation, neo-membrane, fibroblast proliferation, infiltration, or calcification. Conclusions: While the biopsy was reassuring with respect to the absence of EPS, significant histopathological changes suggest that avoiding pH trauma may not ameliorate the effects of glucose exposure in long-term PD.

© 2022 S. Karger AG, Basel

Introduction

The peritoneum provides buoyancy, sliding of the intraperitoneal organs, and is involved in most intra-abdominal conditions. It has a large surface area, measuring 1.5–2.0 m2 in adults. Thirty percent are parietal peritoneum originating from the lateral (parietal) mesoderm and ectoderm, whereas the visceral (splanchnic) peritoneum comes from the mesoderm and endoderm [1]. Most of the research about the peritoneum focuses on the short-term effects of peritoneal dialysis (PD) [2]. Long-term treatment with PD results in peritoneal fibrosis [3], and its worst form is called encapsulating peritoneal sclerosis (EPS), which can be fatal [4-6]. EPS is a rare chronic inflammatory condition characterized by fibrosis and adhesions of the peritoneum to loops of the small intestine, resulting in intermittent, acute, or subacute gastrointestinal obstruction [7]. While the mortality of EPS is lower in children than in adults and surgical treatment is a viable option [4-6, 8, 9], it is dangerous. The European Paediatric Dialysis Working Group suggested a high prevalence of EPS that increases with longer PD vintage [5]. Although the range of morphological alterations is known, these changes vary from patient to patient.

The pathophysiological mechanism of peritoneal fibrosis in EPS is multifactorial. It is characterized by abnormal production of extracellular matrix proteins, leading to progressive thickening of the subesothelial compact zone. Fibrosis may involve neurogenic inflammation involving TGF-β on the visceral peritoneum [10]. There is different innervation of the parietal peritoneum including mesothelial innervation, while the damage mechanism may be predominantly glycation [11]. Risk factors for EPS are low pH solution exposure, glucose degradation products, glucose, abdominal surgery, hemoperitoneum, and peritonitis; resulting in acute/chronic inflammation, progressive fibrosis, angiogenesis, and vasculopathy [12, 13].

Peritoneal biopsies (mostly parietal) determine the severity of fibrosis [14]. The median thickness of the peritoneum in adults at the initiation of PD is 113 μm (interquartile range [IQR] 72–129 μm) [14] but varies with age. Peritoneal thickness is associated with peritoneal transport characteristics (dialysate/plasma creatinine). On ultrasound (US) measurements, the peritoneum was thicker in rapid transporters compared to slow transporters (590 ± 40 μm vs. 270 ± 290 μm, p = 0.01) [15]. Moreover, there is ontogeny of the peritoneal membrane thickness in adolescents, up to 541 μm at the 95th percentile [16].

Serial peritoneal membrane biopsies are not feasible, so US is used instead. Histologically measured and US-estimated thickness are different, the latter being 257 μm thicker [14]. The hyperechoic line generated by US represents the interface between 2 neighboring tissues and not a separate morphological structure. Moreover, since its thickness is influenced by user-defined US settings [14], histology remains the gold standard.

There is ontogeny of the peritoneal membrane thickness with the thickest peritoneum during adolescence (Fig. 1), but there is a paucity of peritoneal biopsy reports in children/adolescents on long-term PD. Younger patients have high transport in the peritoneal membrane, on codextrin clearance [17] or peritoneal equilibration test (PET) [18, 19]. In a study of 110 pediatric PD patients from Turkey, 38 (35%) were high and 29 (26%) were high average transporters [18]. Consequently, most pediatric centers prescribe automated PD with rapid cycles overnight [19]. Using conventional PD solutions causes pH trauma [20], and evidence supports the use of physiologic PD solutions in children who require short dwells, as it takes at least 1 h to equilibrate the pH in the peritoneal cavity [20]. We report a patient with 5 years of PD using physiologic solutions (1.36 and 2.27% PhysionealTM overnight and icodextrin [ExtranealTM] during the day), who underwent a peritoneal biopsy at the time of a PD catheter placement.

Fig. 1.

Percentiles of visceral peritoneal thickness in healthy children, determined by histomorphometry (adapted from [16]).

Case Report/Case Presentation

Caregiver provided written informed consent. A 6-year-old presented with hypertension, hyperlipidemia, nephrotic range proteinuria, and edema. After 2 months of steroid resistance, a kidney biopsy showed primary focal segmental glomerulosclerosis (FSGS). Bacterial peritonitis and posterior reversible encephalopathy complicated the post kidney biopsy course. A gastrostomy tube was endoscopically placed 1-year postdiagnosis to assist with nutrition/growth.

Testing for mutations in the FSGS genes ACTN4, ADCK4, CD2AP, COQ2, INF2, LAMB2, LMX1B, MYH9, NPHS1, NPHS2, PDSS2, PLCE1, SCARB2, SMARCAL1, TRPC6, WT1, and whole-exome sequencing did not show any mutations. Genetic studies identified mutations only in the thiopurine S-Methyltransferase (TPMT) gene, TPMT c.238G>C (p.Ala80Pro), TMPT c.460G>A (p.Ala154Thr), and TMPT c.719A>G (p.Tyr240Cys) which account for low TPMT activity [21]. Genetic work up also revealed a heterozygous variant of unknown significance in the CHFR2 gene (c.215G>A [p.cys72Tyr]).

Nephrotic syndrome remained refractory to cyclosporine, mycophenolate mofetil (MMF), rituximab, tacrolimus, and plasmapheresis. At 7½ years of age, the patient developed pneumococcal pleuritis, thrombotic microangiopathy, and hypertensive posterior reversible encephalopathy syndrome. At age of 8 years, the patient progressed to end-stage kidney disease (ESKD) and commenced PD. The patient’s anemia required high doses of darbepoetin alpha and intermittent iron sucrose intravenously for treatments. However, ferritin levels rose to >6,000 μg/L [normal 14.0–101], so no further iron was given.

The PET revealed high average membrane transport. At age of 9 years and after 1 year of continuous cycling PD with a dwell volume of 1,000 mL/m2 (mainly using 1.36% PhysionealTM overnight and ExtranealTM during the day), the patient received a living, unrelated-donor kidney transplant at another institution. Immunosuppression was with thymoglobulin (induction), tacrolimus, MMF, and prednisone. Because of the history of thrombotic microangiopathy and the variant of unknown significance in the CFHR2 gene, she received eculizumab perioperatively. Nephrotic syndrome recurred within 48 h post-transplant with worsening allograft function and oligo-anuria, but US and surgical exploration did not identify a thrombus. The patient received plasmapheresis (11 sessions in 14 days, followed by 3x weekly for 2 months) and a dose of rituximab (day 24 post-transplant). Renal biopsy at 1-month post-transplant demonstrated mild tubular injury and recurrent FSGS without signs of rejection. She initiated CVVH on postoperative days 3–8 for volume control and was then transitioned to chronic PD as allograft function never recovered. The patient received three blood transfusions with the first transplant.

Two months post-transplant, the patient developed fever and cough. Chest X-ray revealed cardiomegaly. Echocardiography showed a significant (2.2-cm posterior, 1.7-cm left lateral) circumferential pericardial effusion. Peritoneal scintigraphy suggested a peritoneal-pericardial communication [22]. The patient was transitioned to HD. Serial echocardiograms documented resolution of the pericardial effusion over the next 1.5 months without the need for drainage. Eight months after conversion to HD, a thoracic-abdomen CT was completed in preparation for surgical repair of the peritoneal-pericardial communication, and 300 mL of dilute radiographic contrast was instilled through the PD catheter. Images were acquired at 30- and 90-min postinjection, and repeat scintigraphy was performed a week later. Neither contrast nor tracer accumulation was identified in the mediastinum, so PD was resumed without recurrence of the peritoneal-pericardial effusion. There were no other complications for the following 4 years.

The patient maintained the characteristics of a high average transporter by yearly PET on continuous cycling PD X 8–10 h with 40 mL/kg/day well using 1.36 or 2.27% PhysionealTM, a last fill of ExtranealTM, and one daytime dwell of 2.27% PhysionealTM. Ultrafiltration ranged from 1,600 to 2,100 mL/day, and there were no catheter-related infections or peritonitis. The most recent PET revealed high transporter characteristics. There were two mild episodes of peritonitis in October 2017 (Klebsiella oxytoca) and May 2018 (Klebsiella pneumoniae), which were treated promptly.

At age of 13 years, she received a second kidney transplant, again complicated with immediate FSGS recurrence. She initiated CVVH on day 3 post-transplant and transitioned to PD on day 5. However, candidemia and candida peritonitis developed, requiring PD catheter removal and conversion to HD. Repeat plasmapheresis and rituximab failed to improve the FSGS, but there was some response to LDL apheresis plus high-dose methylprednisolone [23]. Urine output and kidney function improved, serum creatinine decreased to 150 μmol/L with a creatinine-based eGFR [24] of 40 mL/min/1.73 m2 [normal 90–135], and HD was successfully discontinued 6 weeks post-transplant. The patient received two additional blood transfusions with the second transplant.

The second graft function was affected by postpolyoma BK virus infection de novo with viral loads up to 20, 000, 000 copies. The patient returned to our institution 3 months post-second transplant with a serum creatinine of 170 μmol/L and cystatin C eGFR of 25 mL/min/1.73 m2 [25], which slowly dropped to 15 mL/min/1.73 m2 [25] over 15 months with a microalbumin/creatinine ratio of 124–660 mg/mmol [normal <2.0], and serum albumin ranging from 31 to 36 g/L [normal 38–54]. The viral load dropped to 800 copies 15 months after lowering the tacrolimus (levels to 3–4 ng/mL), conversion of MMF to leflunomide and intravenous immunoglobulins (0.1 g/kg weekly). As the patient needed tooth extraction and an exploratory laparoscopy for ovarian cysts, it was decided to pre-emptively place a PD catheter and perform a peritoneal membrane biopsy. Surprisingly, the peritoneal membrane looked grossly normal intraoperatively except for one area (Fig. 2). The histology report of the peritoneum was as follows.

Fig. 2.

Laparoscopic image of the visceral peritoneum appearing mostly normal. However, there was one area of lateral peritoneal wall showing a glistening white plaque and presumed sclerosis.

Gross Description

The specimen consists of a single 1.5 × 1.4 × 0.2-cm tan-red-pink fibromembranous piece of tissue with a smooth, shiny surface on one side consistent with the peritoneum.

Microscopic DescriptionLight Microscopy

Sections show fragments of the peritoneum with overlying mesothelium. There is fibrosis and thickening of the submesothelial tissue with significant hemosiderin deposition, as highlighted with Perls Prussian blue histochemical staining. Measurements of the submesothelial compact zone are difficult due to tangential orientation. However, in oriented sections, the thickness is between 200 and 900 μm. The overlying mesothelial cells are intact with no significant denudation. There is a lack of fibrin exudation or fibroblast proliferation, no increase in inflammation, no calcification is identified, no new membrane formation or vascular obliteration.

Immunofluorescence

Sections submitted for direct immunofluorescence testing show negative staining with IgG, IgA, IgM, C3, and fibrinogen.

Diagnosis

Peritoneal fibrosis and hemosiderosis, nonspecific (see comment).

Comment

The histologic findings show a thickened, fibrotic peritoneum (Fig. 3, 4) with significant hemosiderin deposition (Fig. 3 right). The histologic features are nonspecific. While there is morphologic overlap, findings diagnostic of EPS are not identified. Specifically, there is a lack of mesothelial denudation, fibrin exudation, fibroblast proliferation, calcification, or vascular obliteration. Ultimately, EPS is a clinicopathologic diagnosis, and clinical correlation is needed.

Fig. 3.

On the left (a): trichrome stain of peritoneal biopsy showing fibrosis and thickening of the peritoneum, but specific findings of EPS were absent (mesothelial cells were intact, lack of fibrin exudation, no increase in infiltration or calcification, no neomembrane or fibroblast proliferation). On the right (b): histological image showing extensive hemosiderin deposition.

Fig. 4.

Hematoxylin and eosin staining of histological image of the peritoneum including the thickness measurements.

There were no surgical complications, and at last follow-up, 1-month post-PD catheter placement, cystatin C eGFR was 20 mL/min/1.73 m2 [25] and creatinine dropped to 273 μmol/L, so PD is held. The patient continued to require darbepoetin alpha at 30 μg subcutaneously weekly due to normochromic anemia with inadequate reticulocyte counts of 58–74. The average unsaturated iron-binding capacity was 22.0 μmol/L [normal 24.2–70.1]. The average transferrin saturation was 38.2% [normal 11.0–56.0]. The iron level was normal at 7 μmol/L, and ferritin levels over the last year ranged between 86.9 and 124 μg/L [normal 14.0–101].

Discussion

Despite the use of physiologic PD solutions for 5 years and a normal macroscopic appearance of the peritoneum, this patient demonstrated significant fibrosis and hemosiderosis on biopsy. Peritoneal hemosiderosis is a rarely reported finding in pediatric PD patients. ESKD patients receiving chronic intravenous iron products exceeding their blood loss are at an increased risk of positive iron balance [26]. Besbas et al. [27] reported peritoneal hemosiderosis in 4 patients with FSGS who had nephrogenic ascites, but all of these patients were on hemodialysis and received multiple blood transfusions. Our patient received 5 blood transfusions, darbepoetin therapy, no oral iron, and only one intravenous iron dose in the past year. Shortly after the second transplant, the ferritin peaked at 1,600 μg/L. Darbepoetin therapy alone should address iron overload. However, it is unclear if peritoneal iron depositions are in a body compartment from which it cannot be mobilized. The patient also had two episodes of bacterial peritonitis and the candida growth in the PD fluid after the second transplant, which could have contributed to the peritoneal changes; however, Bartosova et al. [11] demonstrated that glucose exposure and dialysis vintage but not peritonitis episodes were responsible for these changes].

A Cochrane review favors physiologic solutions over the older low pH lactate-based solutions [20]. In Ontario, the government has covered the additional cost for PhysionealTM in children/adolescents since 1999. Anecdotally, the principal author in this manuscript has seen four cases of EPS (two were fatal and two improved with total debridement of the visceral peritoneum) [4], and this condition has not been seen since 1999. The literature is scant on peritoneal biopsies in PD patients. Also, there is a solid push to transplant early to reduce dialysis vintage and long-term cardiovascular complications [28]. Ideally, pre-emptive transplantation is pursued in all pediatric cases of ESKD. For instance, despite a high prevalence of aortic dilation, we did not find any cases of this complication in pre-emptively transplanted patients [29].

Peritoneal fibrosis was observed in Wistar rats on long-term PD using standard lactate-based PD solutions, PhysionealTM, and NutrinealTM, but increased expression of vascular endothelial growth factor, microvascular proliferation, or submesothelial fibrosis were not seen, similar to our patient [30]. In another animal study, lymphangiogenesis and lymphatic absorption were related and increased in ESKD, independent of the dialysis solutions, and it seems that ESKD in itself increased the lymph vessel density in a Wistar rat model [31]. Moreover, other toxins such as glucose and glucose degradation products, which cannot be avoided entirely, also can contribute to the findings.

Peritoneal fibrosis is the most consistent finding in patients with long-term PD [32]. In a prospective randomized controlled clinical trial, 80 adult incident PD patients received either a low-glucose regimen comprising PhysionealTM, ExtranealTM, and NutrinealTM (PEN group) or DianealTM (control group) for 12 months, after which both groups continued with DianealTM for 6 months [33]. Only biomarkers of inflammation, especially hyaluronan, were found to be more favorable with physiologic solutions, but no peritoneal biopsies were obtained. Dialysate-to-plasma creatinine ratio at 4-h was higher in the PEN group at 12 months and remained so after switching to DianealTM, suggesting that membranes were better preserved [33]. As such, our patient’s obvious thickening of the peritoneal membrane is disappointing. It seems that the dialysis vintage and ESKD alone may be responsible for the findings. Nonetheless, the patient did not show any other signs of EPS.

Our findings favor the use of physiologic solutions; however, they do not completely avoid changes in the peritoneum. The contribution of the daytime dwells with icodextrin, which has a low pH but gives the peritoneum a break from glucose exposure for multiple hours of the day, is unclear. In Japan, the incidence of EPS decreased from 7.3 to 1.4% of maintenance PD patients in the 1980s to 1.0% in recent years after the introduction of pH neutral physiologic PD solutions[34]. Unfortunately, physiologic PD solutions are not widely available to all children/adolescents with ESKD, for instance, not in the USA [35]. While our patient still developed peritoneal fibrosis and thickening, there were no additional signs of EPS. Unfortunately, physiologic solutions do not abrogate the need for intraperitoneal glucose and exposure to glucose degradation products, apart from ESKD, which probably contributed to the findings.

Conclusions

We report peritoneal membrane histology in an adolescent on long-term PD with peritoneal fibrosis, despite the use of physiologic PD solutions and 14 h of no glucose exposure/day. It seems that after several decades of PD experience, we have made some progress in understanding the peritoneal membrane and long-term repercussions. While new, more biocompatible solutions are available today, albeit not everywhere in the world, it remains to be established if the outcome of long-term PD therapy improves further with the use of these agents. Limitations with the available PD solutions still exist, and continual efforts are needed to develop PD solutions that are more efficient and gentler to the peritoneal membrane.

Acknowledgments

The authors would like to thank the patients and caregivers for allowing us to share this experience in the peer-reviewed literature. We thank Carlos Reis, RN, for collating the PD data and Sarah Lafond, RN, for her valuable editing.

Statement of Ethics

The manuscript was prepared and conducted ethically in accordance with the World Medical Association Declaration of Helsinki. As this is a case report, ethical approval is not required in our institution. Written informed consent was obtained from the patient (consenting minor) and her parents for publication of the details of their medical case and any accompanying images.

Conflict of Interest Statement

The authors have no conflicts of interest to declare. There are no real, potential, or perceived conflicts of interest to report related to this study.

Funding Sources

No funding was available for this study.

Author Contributions

G. Filler and A. Haig conceived the original study idea, provided intellectual insight, and supervision and editing. G. Filler wrote the manuscript and was responsible for all editing and obtaining approval from all authors and developed Figure 1. G. Haig performed and wrote all histopathological studies and provided Figures 3 and 4. N. Merritt performed the surgery, obtained Figure 2, and wrote the surgical part. A.C. Alvarez-Elias and C.W. Teoh wrote the description of the two transplants performed at the Hospital for Sick Children. They also provided major intellectual insight into the study as well as the manuscript editing. T.J. Filler provided the measurements for Figure 1, details on normal and abnormal peritoneal membrane, joined the two histology slides for Figure 3, made the marking and layer description for Figure 3, and provided major intellectual insight into the study as well as the manuscript editing. M.E. Díaz-González de Ferris provided major intellectual insight into the study as well as the manuscript writing and editing of each version. All authors contributed to and approved the final manuscript.

Data Availability Statement

All relevant data have been included in the manuscript. Detailed laboratory findings of the patient would be available from the Electronic Medical Record System at the Children’s Hospital, London Health Sciences, London, ON, Canada, and the Hospital for Sick Children, Toronto, ON, Canada.

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