We report two cases of retroperitoneal fibrosis that emerged during a clinical course of moderate chronic kidney disease. In both cases, we observed an elevation in the serum CRP and IgG4 levels without an increase in the white blood cell count. The patients were treated with prednisolone. Their clinical conditions improved with a decrease in the serum IgG4 to total IgG ratio. The present cases suggest the importance of a differential diagnosis of retroperitoneal fibrosis in the medical care of chronic kidney disease patients, and we propose a useful biomarker for retroperitoneal fibrosis, which we suspect is associated with IgG4-related disease.

Background: Gitelman syndrome (GS) is an autosomal recessive salt-losing renal tubulopathy resulting from mutations in the thiazide-sensitive Na-Cl cotransporter (NCC) gene. Notably, lack of awareness regarding GS and difficulty with prompt diagnosis are observed in clinical practice, particularly in rural settings.Case presentation: We report a case of a 48-year-old man with GS who presented to a local clinic on a remote island. Occasional laboratory investigations incidentally revealed a reduced serum potassium level of 2.6 mmol/L. A careful medical interview revealed episodes of intermittent paralysis of the lower extremities and muscular weakness for >30 years. Subsequent laboratory investigations revealed hypomagnesemia, hypocalciuria, and hypokalemic metabolic alkalosis. Based on the patient’s history, clinical presentation, and laboratory investigations, we suspected GS. Genetic testing revealed a rare homozygous in-frame 18 base insertion in the NCC gene that might have resulted from the founder effect, consequent to his topographically isolated circumstances.Conclusion: More case studies similar to our study need to be added to the literature to gain a deeper understanding of the functional consequences of this mutation and to establish optimal management strategies for this condition, particularly in rural clinical settings.