IgG4-related Retroperitoneal Fibrosis Research Articles

New insights into predictors of autoimmune pancreatitis relapse after steroid therapy

Objectives While autoimmune pancreatitis (AIP) responds well to steroid therapy, the high relapse rate in type 1 AIP remains a critical problem. The present study examined predictors of relapse of type 1 AIP following steroid therapy. Materials and methods Nine factors potentially predictive of relapse were analyzed in 81 AIP patients receiving steroid therapy with follow-up ≥ 12 months. The rate of serum IgG4 decrease following steroid therapy was calculated by dividing the difference between serum IgG4 values before and at two months after the start of steroid by the IgG4 value before steroid. Results A relapse occurred in 11 patients (13.5%) during a median of 38 months. Multivariate analysis revealed that the presence of IgG4-related retroperitoneal fibrosis (HR: 5.59; 95% CI: 1.42–22.0; p = 0.014) and the low rate of serum IgG4 decrease after steroid therapy (HR: 0.048; 95% CI: 0.005–0.46; p = 0.008) were significant, independent predictors of AIP relapse. The cut-off value based on receiver operating characteristic curve data for the rate of serum IgG4 decrease before and at two months after steroid therapy distinguishing patients with and without a relapse was 0.65. Using this cut-off value, the area under the curve, sensitivity, and specificity were found to be 0.63, 0.73, and 0.60, respectively. Conclusion The low rate of serum IgG4 decrease after the start of steroid therapy and the presence of IgG4-related retroperitoneal fibrosis were predictive of type 1 AIP relapse. Cautious, gradual tapering of steroid dosage and longer maintenance therapy are recommended for patients with these factors.

IgG4-related retroperitoneal fibrosis mimicking renal pelvis tumor: a case report and literature review

BackgroundRetroperitoneal fibrosis (RPF) is a rare disease characterized by the development of a fibroinflammatory mass in the retroperitoneum. Immunoglobulin-G4 related RPF was suggested as a secondary form of RPF and thought to be part of the spectrum of Immunoglobulin-G4 related diseases (IgG4-RD). Patients often present to the clinic because of flank pain. Ranging from mild to end-stage renal failure can be observed. The main purpose of treatment is to preserve renal function. As it is a rare condition, there is no definite treatment strategy. We report a case of 39-year-old man with left flank pain and diagnosis of IgG4-related RPF mimicking a renal pelvis tumor.Case presentationA 39-year-old male patient presented with left flank pain. MRI suggested solid retroperitoneal mass associated with hydronephrosis in the left kidney collecting system. Upon identifying the retroperitoneal origin of the mass during nephroureterectomy, the procedure was concluded following the acquisition of frozen section and routine pathological samples from the lesion. In the histopathological examination, inflammatory cells were observed and specific immunohistochemistry for IgG-4 was detected focally positive. Following the placement of a DJ stent, immunosuppressive therapy was initiated with Prednol and Azathioprine. After a one-year follow-up period, during which the patient received immunosuppressive treatment and underwent tri-monthly DJ stent replacements, the DJ stent was subsequently removed, revealing complete regression of hydronephrosis.ConclusionsWith the correct diagnosis and treatment of IgG4-related RPF, it is possible to prevent irreversible complications of the disease. Because it is a rare disease, case reports in the literature will be useful for treatment.

Renal and Urinary Tract Involvement in Fibrosclerosing or Fibroinflammatory Diseases: A Narrative Review

Fibroinflammatory diseases are a group of rare pathologies in which the hallmark is the exuberant deposition of fibrotic tissue and inflammatory cellular infiltrates, characteristic of the specific disease. A sclerotic mass develops within soft tissues and/or organs, damaging and replacing them, with effects ranging from asymptomatic to life-threatening clinical manifestations. The kidneys and urinary tract can be involved in some of these diseases, which can lead to acute kidney injury, chronic kidney disease, and even end-stage kidney disease. IgG4-related disease, retroperitoneal fibrosis, and Erdheim–Chester disease are the three fibroinflammatory disorders that can involve the kidneys. Only a timely and accurate collection of clinical, radiological, metabolic, laboratory, and histological data allows prompt diagnosis and targeted treatment of these pathologies, allowing the stoppage of the evolution of renal and systemic manifestations, which can lead to complete remission. The epidemiology, clinical and histological features, and management of these conditions are herein described in a narrative fashion.

Direct antiglobulin test-negative autoimmune hemolytic anemia associated with erythropoiesis stimulating agent resistance in a CKD patient with IgG4-related disease: A case report

Rationale: Direct antiglobulin test (DAT)-negative autoimmune hemolytic anemia (AIHA) is an important differential diagnosis for erythropoiesis-stimulating agents-resistant renal anemia with hemolysis. Patient concerns: An 82-year-old female with a past medical history of diabetes, end-stage kidney disease (estimated glomerular filtration rate: 6.9 mL/min/1.73 m2), post-transcatheter aortic valve implantation, and IgG4-related retroperitoneal fibrosis on prednisolone therapy was referred to our department for assessment of severe anemia. The patient underwent immunohematological testing for serological evaluation. Diagnoses: DAT-negative AIHA and IgG4-RD was established based on DAT-negative and immunohematological tests. Interventions: Glucocorticoid was administered to the patient. Outcomes: The patient’s condition including hemoglobin level was relieved. Lessons: In chronic kidney disease, AIHA may contribute to the development of severe anemia and erythropoiesis-stimulating agents-resistance, irrespective of the results of Coombs test. Reticulocytosis, undetectable haptoglobin and a fall in hemoglobinA1c despite sustained hyperglycemia may be a clue to the diagnosis of hemolysis.

Reply.

Thank you for your comments in relation to our recently published article “A Case of IgG4- Related Retroperitoneal Fibrosis (IgG4-RPF) with Significant Involvement of the Abdominal Aorta – a Clinical and Diagnostic Challenge.”1

Nationwide epidemiological survey of immunoglobulin G4-related disease with malignancy in Japan.

To clarify the clinicoepidemiological characteristics of immunoglobulin G4 (IgG4)-related disease (IgG4-RD) with malignancy, a nationwide epidemiological survey was conducted. Immunoglobulin G4-related disease patients with malignancy who had visited selected hospitals in Japan were surveyed. The study consisted of two stages: the number of IgG4-RD patients with malignancy was estimated by the first questionnaire and their clinicoepidemiological characteristics were assessed by the second questionnaire. The frequencies of autoimmune pancreatitis (AIP), IgG4-related sialadenitis, IgG4-related eye disease, IgG4-related kidney disease, and IgG4-related retroperitoneal fibrosis were 44.7%, 20.8%, 14.0%, 5.16%, and 5.12%, respectively. The overall prevalence of malignant disease in IgG4-RD cases was estimated to be 10900 per 100000 cases, which was significantly higher than that of malignant disease in the general population. The prevalence of malignant lymphoma in IgG4-RD cases was the highest and was estimated to be 1985 per 100000 cases. IgG4-related kidney disease had the highest frequency of malignant disease (17.1%). In data from 200 patients, 61 (30.5%) cases of cancer were found 2years or more before the IgG4-RD diagnosis, 92 cases (46%) during the 1year preceding or following IgG4-RD diagnosis, and 62 cases of cancer (31%) 2 or more years following IgG4-RD diagnosis. The nationwide survey for IgG4-RD with malignancy in Japan showed that IgG4-RD may be related with malignant diseases.

A case of IgG4-related retroperitoneal fibrosis diagnosed by tissue biopsy

A case of IgG4-related retroperitoneal fibrosis diagnosed by tissue biopsy

IgG4-Related Sclerosing Cholangitis: Rarely Diagnosed, but not a Rare Disease.

IgG4-related sclerosing cholangitis, a biliary manifestation of an IgG4-related disease, belongs to the spectrum of sclerosing cholangiopathies which result in biliary stenosis. It presents with signs of cholestasis and during differential diagnosis it should be distinguished from cholangiocarcinoma or from other forms of sclerosing cholangitis (primary and secondary sclerosing cholangitis). Despite increasing information and recently established diagnostic criteria, IgG4-related sclerosing cholangitis remains underdiagnosed in routine clinical practice. The diagnosis is based on a combination of the clinical picture, laboratory parameters, histological findings, and a cholangiogram. Increased serum IgG4 levels are nonspecific but are indeed a part of the diagnostic criteria proposed by the Japan Biliary Association and the HISORt criteria for IgG4-SC. High serum IgG4 retains clinical utility depending on the magnitude of elevation. Approximately 90% of patients have concomitant autoimmune pancreatitis, while 10% present with isolated biliary involvement only. About 26% of patients have other organ involvement, such as IgG4-related dacryoadenitis/sialadenitis, IgG4-related retroperitoneal fibrosis, or IgG4-related renal lesions. A full-blown histological finding characterized by IgG4-enriched lymphoplasmacytic infiltrates, obliterative phlebitis, and storiform fibrosis is difficult to capture in practice because of its subepithelial localization. However, the histological yield is increased by immunohistochemistry, with evidence of IgG4-positive plasma cells. Based on a cholangiogram, IgG-4 related sclerosing cholangitis is classified into four subtypes according to the localization of stenoses. The first-line treatment is corticosteroids. The aim of the initial treatment is to induce clinical and laboratory remission and cholangiogram normalization. Even though 30% of patients have a recurrent course, in the literature data, there is no consensus on chronic immunosuppressive maintenance therapy. The disease has a good prognosis when diagnosed early.

SIGNIFICANCE OF IgG4 IN IDIOPATHIC RETROPERITONEAL FIBROSIS

(Objective)Retroperitoneal fibrosis is largely divided into the idiopathic and secondary types. Some idiopathic cases include IgG4-related diseases, which are often similar to malignant diseases, such as lymphoma and sarcoma. The diagnostic criteria for IgG4-related disease are used and pathologic examination is necessary for a definitive diagnosis of IgG4-related retroperitoneal fibrosis. The first choice of treatment for IgG4-related retroperitoneal fibrosis is steroid administration, but no consensus has been established regarding its dose and tapering schedule. We investigated the significance of IgG4 in diagnosis and treatment of idiopathic retroperitoneal fibrosis. (Patients and methods)We examined 14 cases diagnosed as idiopathic retroperitoneal fibrosis between April 2013 and March 2019. Serum IgG4 was measured at the time of diagnosis in 13 cases, and changes over time in serum IgG4 before and after the induction of steroid therapy were measured in 6 cases. Computed tomography-guided biopsy was performed on 4 cases. (Results)Of all cases, 1 patient was diagnosed as IgG4-related retroperitoneal fibrosis and 5 patients were classified as possible group. Ten patients were administered steroid therapy. Percutaneous nephrostomy tube was placed in 3 patients and was removed in 2 of these patients after steroid therapy. The serum high levels of IgG4 were confirmed in all 4 patients who were classified into the possible group and who were treated with steroids. (Conclusion)Although histologic examination is necessary for the diagnosis of retroperitoneal fibrosis, tissue collection by open or laparoscopic surgery is highly invasive. CT-guided biopsy may be useful in high-risk cases, such as elderly patients on anticoagulation. After excluding other diseases in high-risk cases, response to empiric steroid therapy may be diagnostic. In the possible group, changes in serum IgG4 levels may reflect the disease condition and might be useful in determining the maintenance dose of steroids.

Renal Involvement in Retroperitoneal Fibrosis: Prevalence, Impact and Management Challenges.

Retroperitoneal fibrosis (RPF) is a rare disorder consisting of idiopathic and various secondary forms and characterized by chronic inflammatory infiltrates and marked fibrosis in the retroperitoneal space. In idiopathic RPF (IRPF), 35–60% of cases have been reported to be IgG4-related RPF, the retroperitoneal lesions of IgG4-related disease (IgG4-RD). IRPF can frequently lead to renal insufficiency mediated by urinary tract obstruction and hydronephrosis irrespective of being IgG4-related or not. Clinical pictures, laboratory and imaging findings, and location of the urinary tract obstruction are generally similar in IgG4-related and non-IgG4-related IRPF although multiple organ involvement and serum IgG4 elevation may be characteristic of the IgG4-related forms. Periaortic/periarterial lesions are the most frequent cause of renal insufficiency. Although the response to glucocorticoids is generally good, relapse does occur in a considerable proportion of patients, and may require an additional immunosuppressive agent and/or urological intervention in cases with multiple relapses or refractory obstructive uropathy. In general, the prognosis of patients with IRPF is good, but careful attention needs to be paid to chronic kidney disease as a major complication and rupture of the affected aorta/artery as a life-threatening one. Further studies are necessary to better understand the pathogenesis of the disease and to establish the optimal diagnostic and therapeutic strategies for it.

IgG4-related retroperitoneal fibrosis: a condition commonly overlooked in daily clinical practice.

IgG4-related retroperitoneal fibrosis: a condition commonly overlooked in daily clinical practice.

Clinical characteristics of IgG4-related retroperitoneal fibrosis versus idiopathic retroperitoneal fibrosis.

Retroperitoneal fibrosis (RPF) is an uncommon condition characterized by inflammation and fibrosis in the retroperitoneal space. More than two-thirds of RPF are idiopathic, with the remaining stemed from a variety of secondary causes. It was suggested that IgG4-related RPF is a secondary form of RPF. We undertook this study to compare detailed demographic, clinical and laboratory characteristics of IgG4-related RPF and IRPF in a large Chinese cohort. We retrospectively reviewed the medical records of 132 RPF patients diagnosed at Peking University People’s Hospital between March 2010 and March 2018. Among the 132 patients, the mean age at disease onset was 54.8 years. IgG4-related RPF group showed greater male predominance compared to IRPF group. IgG4-related RPF patients showed a longer interval between symptom onset and diagnosis, and allergic diseases were more common in this group. Sixty-four patients (48.4%) had lower back pain, which was more common in IRPF group than that in IgG4-related RPF patients. In terms of organ involvement, although 42 of 47 patients (89.3%) with IgG4-related RPF had other organ involvement, there were no patients in the IRPF group with other organ involvement. In addition, the serum IgG4 level, elevated eosinophils counts and IgE level were significantly higher in IgG4-related RPF patients. We described the demographic, clinical and laboratory differences between IgG4-related RPF and IRPF patients, indicating their potential differences in pathogenesis, which was of great importance to diagnose and manage the two phenotypes.

IgG4相关腹膜后纤维化致急性肾损伤和硬化性胆管炎1例及文献复习

IgG4相关腹膜后纤维化致急性肾损伤和硬化性胆管炎1例及文献复习

Clinical features of IgG4-related retroperitoneal fibrosis among 407 patients with IgG4-related disease: a retrospective study.

IgG4-related disease (IgG4-RD) is recently recognized as a fibro-inflammatory condition featured by tumefactive lesions in multiple organs, and the retroperitoneum is one of the common involved sites. We undertook this study to compare detailed demographic, clinical and laboratory characteristics of IgG4-RD patients with retroperitoneum lesion (IgG4-RD RPF+) and retroperitoneum free IgG4-RD (IgG4-RD RPF-) in a large cohort. We carried out a retrospective review of the medical records of 407 cases of IgG4-RD diagnosed at Peking University People's Hospital between March 2009 and May 2019. Among 407 patients, 58 had retroperitoneum affected. As compared with IgG4-RD RPF- patients, IgG4-RD RPF+ patients showed older age at disease onset and diagnosis. IgG4-RD RPF+ group involved more male patients. In terms of organ involvement, IgG4-RD RPF+ group was more frequently presented with kidney involvement, while salivary gland, lacrimal gland and pancreas were more prominent in the IgG4-RD RPF- group. In addition, the CRP, ESR level and creatinine level were significantly higher in IgG4-RD RPF+ patients, and hypocomplementemia were more common in this group. We have revealed demographic, clinical and laboratory differences between IgG4-RD RPF+ and RPF- patients, which indicated potential differences in pathogenesis and important implications for the diagnosis and management of these two phenotypes.

IgG4-related focal retroperitoneal fibrosis in ureter suggestive of colon cancer recurrence and resected laparoscopically: a case report

BackgroundImmunoglobulin G4-related disease (IgG4-RD) is a novel disease concept of unknown cause that is characterized by abundant infiltration of IgG4-positive cells, mass-forming lesions, and elevated serum IgG4 levels. The infiltration of IgG4-positive plasma cells and lymphocytes causes swelling, inflammation, fibrosis, and obliterative phlebitis in multiple organs. On the other hand, IgG4-RD occurring in the ureters has rarely been reported. To our knowledge, this is the first report of laparoscopic partial ureteral resection for IgG4-related focal retroperitoneal fibrosis in a ureter with suspected colon cancer recurrence.Case presentationA 72-year-old man with a history of sigmoid colon cancer visited Shiga University of Medical Science Hospital for regular follow-up in December 2019. Enhanced abdominal computed tomography revealed a mass involving the left ureter. Furthermore, fluorine-18 fluorodeoxyglucose positron emission tomography showed significant accumulation of fluorodeoxyglucose uptake in the same region. Due to the possibility of colon cancer recurrence, a laparoscopic excisional biopsy with partial ureteral resection was performed. Histologically, IgG4-positive plasma cell infiltration exceeding 10 cells per high-power field and a high ratio of IgG4-positive/IgG-positive cells exceeding 40% were observed. The postoperative serum IgG4 level was 384 mg/dL. With the application of these findings to the diagnostic algorithm in the comprehensive diagnostic criteria for IgG4-RD, the mass-forming lesion was diagnosed as definitive IgG4-related focal retroperitoneal fibrosis.ConclusionsIgG4-RD should be considered in the differential diagnosis of retroperitoneal lesions. Moreover, laparoscopic surgery may be useful for making the diagnosis in difficult-to-biopsy cases.

In vitro IL-6/IL-6R Trans-Signaling in Fibroblasts Releases Cytokines That May Be Linked to the Pathogenesis of IgG4-Related Disease.

Background: The remarkable mechanisms of storiform fibrosis and the formation of high levels of IgG4 with a pathogenic germinal center (GC) in the inflammatory tissue of IgG4-RD remains unknown and may be responsible for the unsatisfactory therapeutic effect on IgG4-related diseases when using conventional therapy.Objectives: To investigate the mechanisms of interleukin 6 (IL-6) inducing fibroblasts to produce cytokines for pathogenic GC formation in the development of IgG4-related disease (IgG4-RD).Methods: The clinical data and laboratory examinations of 56 patients with IgG4-RD were collected. IL-6 and IL-6R expression in the serum and tissues of patients with IgG4-RD and healthy controls were detected by ELISA, immunohistochemistry, and immunofluorescence. Human aorta adventitial fibroblasts (AAFs) were cultured and stimulated with IL-6/IL-6 receptor (IL-6R). The effect of IL-6/IL-6R on AAFs was determined by Luminex assays.Results: The serum IL-6 and IL-6R levels were elevated in active IgG4-RD patients and IL-6 was positively correlated with the disease activity (e.g., erythrocyte sedimentation rate [ESR], C-reactive protein [CRP], and IgG4-RD responder index). IL-6 and IL-6R expression in the tissue lesions of IgG4-related retroperitoneal fibrosis and IgG4-related sialadenitis patients were also significantly higher than that in the normal tissues. In addition, there is a relative abundance of myofibroblasts as well as IgG4+ plasma cells in the tissues of IgG4-related retroperitoneal fibrosis. α-SMA and B cell differentiation cytokines (i.e., B cell activating factor), and α-SMA and T follicular helper (Tfh) cell differentiation cytokines (e.g., IL-7, IL-12, and IL-23) were co-expressed in the local lesions. In vitro, IL-6/IL-6R significantly promoted the production of B cell activating factor, IL-7, IL-12, and IL-23 in AAFs in a dose-dependent manner. This effect was partially blocked by JAK1, JAK2, STAT3, and Akt inhibitors, respectively.Conclusions: In vitro IL-6/IL-6R trans-signaling in fibroblasts releases Tfh and B cell differentiation factors partially via the JAK2/STAT3, JAK1/STAT3, and JAK2/Akt pathways, which may be linked to the pathogenesis of IgG4-RD. This indicated that IL-6 and fibroblasts may be responsible for GC formation and fibrosis in the development of IgG4-RD. Blocking IL-6 with JAK1/2 inhibitors or inhibiting fibroblast proliferation might be beneficial for IgG4-RD treatment.

SUN-326 CLINICAL MANIFESTATIONS AND LONG-TERM OUTCOMES OF IGG4-RELATED KIDNEY AND RETROPERITONEAL INVOLVEMENT IN A UNITED KINGDOM IGG4-RELATED DISEASE COHORT

IgG4-related disease (IgG4-RD) is a relapsing multisystem fibro-inflammatory disease, which may involve the kidney (IgG4-related kidney disease; IgG4-RKD) and retroperitoneum (IgG4-related retroperitoneal fibrosis; IgG4-RPF). Cohorts of patients with IgG4-RKD and IgG4-RPF have been reported in North America and Asia, but the features of renal involvement in Europe are yet to be described. We undertook this study to describe the clinical characteristics and outcomes of renal and retroperitoneal involvement in a cohort of IgG4-RD patients from the United Kingdom (UK).

IgG4-related Retroperitoneal Fibrosis: An Emerging Masquerader With a Sinister Presentation

ObjectiveRetroperitoneal fibrosis (RPF) is a rare proliferative fibro-inflammatory disease involving the soft tissues of the retroperitoneum. IgG4 related retroperitoneal fibrosis is an emerging entity which needs to be distinguished from idiopathic RPF. We describe a clinical case of IgG4 related RPF highlighting the importance of clinching this diagnosis. MethodsA 70 year old female was referred to the outpatient department of our institute with complaints of fatigue, bilateral flank pain and loss of appetite for the past 1 month. The CT and PET scan demonstrated a uniformly enhancing bulky retroperitoneal mass causing bilateral hydroureteronephrosis. The biopsy from the mass lesion revealed IgG4 related disease. The patient was started on corticosteroids after percutaneous nephrostomy placement. ResultsThree months post induction of therapy, repeat PET-CT shows resolution of the mass with no FDG avid lesion. Serum IgG4 levels were reduced to normal (27 mg/dL) suggestive of response to treatment. The percutaneous nephrostomies were removed and the patient is doing well on maintenance dose of corticosteroids for her disease. ConclusionThe availability of serum IgG4 levels for monitoring treatment response and follow-up can curtail the repeated radiological imaging and associated contrast exposure as compared to idiopathic RPF. Secondly, the diagnosis of IgG4-related RPF shall alert the clinician to look out for extra-retroperitoneal diseases on follow up of this multi-organ disease.

Relapse patterns and predictors of IgG4-related diseases involved with autoimmune pancreatitis: A single-center retrospective study of 115 patients.

Autoimmune pancreatitis is an autoimmune disorder accompanied by clinicopathological manifestations that have been established as immunoglobulin (IgG)4-related diseases (IgG4-RD). Other IgG4-RD are often involved with autoimmune pancreatitis. They sometimes relapse despite a favorable response to steroid therapy. This study aimed to clarify the patterns and risk factors for extrapancreatic relapse. We reviewed the data of 115 patients diagnosed with definite autoimmune pancreatitis type 1 and followed up for > 1 year. We analyzed two items: the timing and pattern of extrapancreatic relapse, and risk factors for relapse with three common manifestations: IgG4-related sclerosing cholangitis (SC), IgG4-related dacryoadenitis and sialadenitis (DS), and IgG4-related retroperitoneal fibrosis (RF). Remission was achieved in all patients, except one. The extrapancreatic relapse rates were 11.0%, 19.7%, and 40% within 3, 5, and 10 years, respectively. Of 26 patients with extrapancreatic relapse, nine (34.6%) relapsed with a new IgG4-RD. Based on multivariate analysis, the interval between symptom onset and steroid initiation, and the presence of RF at onset were significant risk factors for relapse with SC and RF, respectively. Our results indicate that they may be various extrapancreatic relapse patterns especially in autoimmune pancreatitis with other organ involvement. Patients with a delayed initiation of steroids or RF at onset should be carefully followed up as high-risk groups for SC and RF relapse.

Retroperitoneal fibrosis in the era of immunoglobulin G4-related disease.

BackgroundRetroperitoneal fibrosis (RPF) is a rare disease characterized by fibroinflammatory tissue in the periaortic or periiliac retroperitoneum, where it frequently encases ureters. There is emerging evidence that a subset of this disease is part of a spectrum of multisystemic autoimmune diseases collectively referred to as “immunoglobulin G4 (IgG4)-related disease”.MethodsWe retrospectively analyzed 27 idiopathic RPF patients and identified a subset as IgG4-related RPF, which we categorized according to recently published comprehensive diagnostic criteria. We compared clinical and laboratory characteristics and response to treatment between the two groups.ResultsOf 27 total patients, 16 (59.3%) were diagnosed as having IgG4-related RPF, and these were predominantly male. They were also significantly older and more likely to have other organ involvement, hydronephrosis, and postrenal acute kidney injury (AKI) compared to those with idiopathic RPF. However, there was no difference in response rate to systemic steroid treatment.ConclusionIgG4-related RPF accounts for a substantial portion of RPF cases previously identified as “idiopathic RPF” in Korea. Clinical and laboratory characteristics of IgG4-related RPF are similar to those of idiopathic RPF except for a striking male predominance, older age, and higher incidence of postrenal AKI in IgG4-related RPF. More comprehensive, prospective studies are needed to clearly distinguish IgG4-related RPF from idiopathic RPF based on clinical manifestation and to further assess treatment response and long-term prognosis.