Xanthogranulomatous Pyelonephritis in Peritoneal Dialysis.

Introduction: Xanthogranulomatous pyelonephritis (XGP) is a rare illness that consists of a destructive chronic inflammatory process of the renal parenchyma associated with recurrent infection and obstructions of the urinary tract. Peritoneal dialysis (PD) is a form of renal replacement therapy used in advanced kidney disease. PD patients demonstrate a systemic inflammatory state, secondary to the increase in uremic toxins, decreased filtration of proinflammatory cytokines, as well as constant exposure to bioincompatible dialysis solutions or a foreign body reaction from the catheter, among other factors, as peritoneal infections. Case Presentation: We present the clinical case of a 74-year-old woman, with a history of recurrent urinary tract infections associated with nephrolithiasis and stage 5D chronic kidney disease, on a PD program. The patient presented a non-specific 3-month state of progressive asthenia, with increased inflammatory parameters in the analytical controls. After presenting multiple negative urine cultures and peritoneal fluid cultures, she was hospitalized to study the constitutional syndrome. The imaging test revealed bilateral staghorn lithiasis with severe dilatation of the right renal pelvis and great cortical thinning. Given the suspicion of XGP, it was decided to perform right renal nephrectomy, which was confirmed after the anatomopathological study. Prior to the intervention, she was transferred to hemodialysis. Over the following months, significant clinical and analytical improvement was observed. Conclusion: The systemic inflammatory state and the risk of infections in PD can mask the diagnosis of XGP in PD patients. There are no reported cases of XGP in patients in PD.

Genetic testing in focal segmental glomerulosclerosis: in whom and when?

Background: Genetic causes are increasingly recognized in patients with focal segmental glomerulosclerosis (FSGS), but it remains unclear which patients should undergo genetic study. Our objective was to determine the frequency and distribution of genetic variants in steroid-resistant nephrotic syndrome FSGS (SRNS-FSGS) and in FSGS of undetermined cause (FSGS-UC). Methods: We performed targeted exome sequencing of 84 genes associated with glomerulopathy in patients with adult-onset SRNS-FSGS or FSGS-UC after ruling out secondary causes. Results: Seventy-six patients met the study criteria; 24 presented with SRNS-FSGS and 52 with FSGS-UC. We detected FSGS-related disease-causing variants in 27/76 patients (35.5%). There were no differences between genetic and non-genetic causes in age, proteinuria, glomerular filtration rate, serum albumin, body mass index, hypertension, diabetes or family history. Hematuria was more prevalent among patients with genetic causes. We found 19 pathogenic variants in COL4A3-5 genes in 16 (29.3%) patients. NPHS2 mutations were identified in 6 (16.2%) patients. The remaining cases had variants affecting INF2, OCRL, ACTN4 genes or APOL1 high-risk alleles. FSGS-related genetic variants were more common in SRNS-FSGS than in FSGS-UC (41.7% vs 32.7%). Four SRNS-FSGS patients presented with NPHS2 disease-causing variants. COL4A variants were the most prevalent finding in FSGS-UC patients, with 12 patients carrying disease-causing variants in these genes. Conclusions: FSGS-related variants were detected in a substantial number of patients with SRNS-FSGS or FSGS-UC, regardless of age of onset of disease or the patient's family history. In our experience, genetic testing should be performed in routine clinical practice for the diagnosis of this group of patients.