AKI in IgG4-Related Retroperitoneal Fibrosis: A Case Report

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Introduction: IgG4 related disease is a chronic fibro-inflammatory disease with multiorgan involvement. Although a multisystem disease, renal involvement is the most common presentation, exhibiting the features of tubulointerstitial nephritis.The pathological hallmark of the disease is dense lymphoplasmacytic infiltrate with elevated IgG4 positive plasma cells. First line treatment for IgG4-RKD is steroids and any delay in the treatment can lead to irreversible kidney damage, necessitating early diagnosis and prompt treatment. Case Description: A 35 year old male presented with weight loss, unexplained anemia, and generalized lymphadenopathy.On admission, laboratory investigations revealed :BUN/Cr 72/12 and K+5.9. Urinalysis was unremarkable and Renal Ultrasonogram revealed moderate to severe hydronephrosis bilaterally. CT scan revealed new proliferative abnormal soft tissue in the lower retroperitoneum and bilateral iliac regions, suggesting retroperitoneal fibrosis with bilateral ureteral obstruction which was not present in the previous scans two months prior to presentation. Initial diagnosis of post-renal AKI was managed with nephrostomy tube placement and a single dialysis session. Anemia evaluation showed positive ANA (1:80) and elevated total protein (9.0 mg/dL), IgG (3107 mg/dL) and IgA (492 mg/dL) with no M spike on SPEP. Further IgG subtyping showed mildly elevated IgG4 (101 mg/dL). A diagnosis of idiopathic retroperitoneal fibrosis was made after all other differentials were ruled out. Discussion: IgG4-RD has a rare incidenceof less than 1 per 100,000 population.Renal damage in IgG4-RD can be attributed to direct parenchymal damage or retroperitoneal fibrosis around the ureters resulting in hydronephrosis and post renal AKI, as seen in our patient. A comparative analysis from past CT scan showed diffuse retroperitoneal fibrosis around the external, common and internal iliac arteries and mesenteric arteries, indicating the severity and rapidly progressive nature of the disease. Following a treatment plan with high dose steroids, there was no significant response as evidenced by a repeat CT scan showing fibrosis in multiple areas throughout the body. As per treatment protocol, the patient was started on four week Rituximab therapy with tapering steroid and weekly Methotrexate. The patient currantly has stable disease based on repeat imaging and levels of inflammatory markers.

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