Light-microscopic characteristics of IgG4-related tubulointerstitial nephritis: distinction from non-IgG4-related tubulointerstitial nephritis

Plasma Cell-rich Nephritis with a Systemic Polyclonal Lymphoproliferative Disorder, Mimicking Idiopathic Multicentric Castleman Disease, Systemic Lupus Erythematosus, and IgG4-related Disease

Idiopathic multicentric Castleman disease (iMCD), systemic lupus erythematosus (SLE), and IgG4-related disease (IgG4-RD) can cause lymphadenopathy with renal involvement. As no gold standards have been set for diagnosing these conditions, diagnoses can be made by excluding other conditions. However, some cases are difficult to identify. A 60-year-old man presented with lymphadenopathy, renal dysfunction, and hypocomplementemia. Autoimmune pancreatitis and iMCD had been suspected. A renal biopsy revealed immune complex-mediated glomerulonephritis superimposed on endothelial injury and plasma cell-rich tubulointerstitial nephritis with storiform-like fibrosis. While the features of iMCD, SLE, and IgG4-RD were present, a clear classification could not be achieved.

Relationship between MRI findings and renal histopathology in IgG4-related tubulointerstitial nephritis

OBJECTIVES

Magnetic resonance imaging (MRI) is expected to be a valuable tool for evaluating disease activity in immunoglobulin G4 (IgG4)-related tubulointerstitial nephritis (IgG4-TIN). However, the correlation between MRI findings and renal histopathological findings remains to be elucidated. This study aimed to clarify the correlation.

METHODS

This retrospective cross-sectional study investigated 26 patients with biopsy-proven IgG4-TIN who underwent simultaneous percutaneous kidney biopsies and abdominal MRI examinations. We reviewed kidney biopsy specimens and scored the degree of inflammatory cell infiltration and interstitial fibrosis. We assessed abdominal MRI, specifically examining T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), and diffusion-weighted imaging (DWI), for the presence of abnormal signals in the inferior pole of the kidney. Spearman's correlation coefficient test was conducted to examine the relationship between the images and histological findings.

RESULTS

For T1WI, eight cases showed a positive low-intensity signal, and 18 cases were negative. For T2WI, 19 cases were positive for a low-intensity signal, and seven cases were negative. In DWI, 23 cases were positive for a high-intensity signal, and one was negative. T1WI low-intensity signal and T2WI low-intensity signal were significantly correlated with interstitial fibrosis score (correlation coefficients 0.52 and 0.64).

CONCLUSION

Low-intensity signal on T2WI is useful for predicting the degree of fibrosis in IgG4-TIN.

Tubulointerstitial nephritis with storiform fibrosis in a patient with angioimmunoblastic T-cell lymphoma

We present a case of an angioimmunoblastic T-cell lymphoma (AITL) and tubulointerstitial nephritis with storiform fibrosis in a 76-year-old man. The patient exhibited lymphadenopathy, polyclonal hypergammaglobulinemia, and renal dysfunction and was diagnosed with AITL on the basis of lymph node biopsy findings. The serum IgG4 level was highly elevated. Renal biopsy revealed IgG4-positive plasma cells and storiform fibrosis without infiltration of AITL, and the findings indicated IgG4-related kidney disease (IgG4-RKD). Following THPCOP therapy for AITL, the renal function improved. While diagnosing IgG4-RKD in a patient with AITL poses challenges, follicular helper T cell involvement appeared crucial in AITL and renal tubulointerstitial lesions in this case.

Tubulointerstitial nephritis: a biopsy case series of 139 Japanese patients

BACKGROUND

Tubulointerstitial nephritis (TIN) is an important cause of acute kidney injury (AKI) and advanced CKD. Only a limited number of studies have reported etiology-based differences in the clinical and/or histopathological properties and kidney outcomes of the biopsy-proven TIN.

METHODS

Patients with biopsy-proven TIN identified from 2005 to 2016 in five hospitals were categorized based on the etiologies and were retrospectively analyzed in relation to the clinicopathological findings and kidney outcomes.

RESULTS

Among 4815 biopsy cases screened, 153 Japanese TIN patients were identified, of whom 139 patients with ≥ 6 months of follow-up data (median 58 years old, 45.3% female, median 31.5 months follow-up) were further analyzed. TIN was drug-induced in 32.4%, autoimmune-related in 24.5%, of unknown etiology in 27.3% and other disease-related in 15.8%. Non-steroidal anti-inflammatory drugs and antibiotics were major causative drugs in drug-induced TIN, and IgG4-related disease, Sjögren's syndrome and sarcoidosis were common in autoimmune-related TIN. Among etiology groups, drug-induced TIN showed advanced AKI with elevated serum creatinine (sCr) and increased C-reactive protein levels at the diagnosis. TIN patients with autoimmune diseases showed less-severe AKI, but were more frequently treated with corticosteroids than others. Tubulointerstitial injury expansion in biopsy specimens was comparable among the groups. Complete or partial kidney function recovery at 6 months was more frequent in drug-induced and autoimmune-related TIN than in others. sCr levels at 6 months were similar among the groups.

CONCLUSIONS

This largest case series study of the biopsy-proven TIN in Japan provides detailed information regarding both etiology-based clinicopathological properties and kidney outcomes.

Active IgG4-related disease with bone marrow involvement: a report of 2 cases and case-based review

IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory disease, histopathologically characterized by dense lymphoplasmacytic infiltration rich in IgG4-positive plasma cells in affected organs. Classic hematologic presentations including lymphadenopathy, eosinophilia and polyclonal hypergammaglobulinemia are common, whereas bone marrow involvement of IgG4-RD is rarely reported. Here we present two patients of multi-organ IgG4-RD with bone marrow involvement, one on bone marrow biopsy, and the other on PET/CT. Presentations of other organ involvement included biopsy-proven IgG4-related tubulointerstitial nephritis, lymphadenopathies, submaxillary glands, arteritis, asthma, dysosmia, and constitutional symptoms. Bone marrow involvement was initially suspected due to leukopenia, anemia and thrombocytopenia in case#1, and was finally confirmed by histological evidence of significant IgG4-positive plasma cells infiltration in bone marrow. In case#2, we incidentally observed high uptakes of multi-bone marrow on ¹⁸F-FDG-PET/CT, with the maximum SUV value similar to that of the kidneys, submaxillary glands and hilar, mediastinal lymph nodes by ¹⁸F-FDG-PET/CT. Symptoms and all the hematologic presentation improved rapidly in both patients after steroids initiation. These two cases illustrate the rare bone marrow involvement in active IgG4-RD accompanied by other hematologic syndromes. The significance of disease pathogenesis is worthy of further study.

Clinicopathological Patterns and Predictors of the Functional Restoration of Immunoglobulin G4-Related Kidney Disease: A Chinese Single-Center Cohort Study

Background: Immunoglobulin G4-related disease (IgG4-RD) is a systemic immunoreactivity-based fibro-inflammatory disease. Immunoglobulin G4-related kidney disease (IgG4-RKD) is a frequently overlooked diagnosis. This study aimed to describe IgG4-RKD and examine the factors relevant to the renal outcomes of IgG4-RD. Methods: We studied a prospective IgG4-RKD cohort between January 2012 and December 2020 with close follow-up. Clinicopathologic data at kidney biopsy were collected and analyzed. We aimed to explore independent risk factors for long-term renal outcome and disease relapse. Patients with an eGFR<45 ml/min per 1.73m2 at 12 months were defined as having poor outcomes. Results: The included 42 patients with IgG4-RKD had a mean age of 58.5 ± 8.7 years (male-to-female ratio = 5:1). The IgG4-RD responder index (RI) was 12.2 ± 3.3. A total of 66.7% of the patients presented with acute on kidney disease or acute on chronic kidney disease. Eight patients (19.0%) showed nephrotic-range proteinuria, and nine (21.4%) had high-titer IgG4-autoantibodies, including antineutrophil cytoplasmic antibody and anti-phospholipase A2 receptor. A kidney biopsy was conducted in 40 patients. Thirty-seven (90.0%) patients were diagnosed with IgG4-related tubulointerstitial nephritis, and 19 (47.5%) of them had concurrent glomerular diseases (membranous nephropathy [MN], n = 3; crescentic glomerulonephritis [CrGN], n = 11; diabetic kidney disease, n = 3; and both MN and CrGN, n = 2). IgG4-RD RI had a close relationship with serum C3 (R = -0.509, P = 0.001), C4 (R = -0.314, P = 0.049) levels, and peripheral blood eosinophil count (PBEC; R = 0.377, P = 0.024), factors that were not included in RI scores. Correlation analysis disclosed that IgG4-RD RI (R = 0.422, P = 0.007), organs involved (R = 0.452, P = 0.003), and C3 (R = -0.487, R = 0.002) were correlated with the percentage decrease of serum creatinine at 1 month. However, multivariate regression analysis failed to identify any clinicopathological parameters that could predict short-term renal restoration and IgG4-RKD relapse. Ten out of 29 variables, of most importance, were identified by the least absolute shrinkage and selection operator (LASSO) regression analysis. By multivariate logistic regression a higher serum IgG4 (OR = 0.671, P = 0.010), IgG1 (OR = 1.396, P = 0.049), IgG3 (OR = 19.154, P = 0.039), and erythrocyte sedimentation rate (ESR; OR = 1.042, P = 0.032) were found to be independent factors for poor long-term outcome. Conventional immunosuppressive medications and/or rituximab were prescribed, and in 83.3% of the patients, the kidney function improved. Repeat kidney biopsies confirmed the remission of interstitial inflammation in two patients under immunosuppressive therapy. However, the disease relapse rate was as high as 31.0%. Conclusions: We strongly recommend a kidney biopsy in active IgG4-RD, especially when there is proteinuria and renal dysfunction, because concurrent glomerular involvement and active interstitial inflammation should be assessed. A higher serum IgG1, IgG3, and ESR were independent factors for the poor long-term renal outcome; however, elevated IgG4 predicted a good renal prognosis, and appropriate and timely immunosuppressive therapy can help achieve a better prognosis.

Case Report: Predominant Tubulointerstitial Lupus Nephritis or the Combination With IgG4-Related Disease?

Isolated or dominant tubulointerstitial lupus nephritis is rare. Here, we reported a 67-year-old man diagnosed with systemic lupus erythematosus (SLE) based on clinical and laboratory criteria, who was showing impaired renal function and non-nephrotic range proteinuria in the past 2 years. Renal biopsy showed almost normal glomeruli, but the tubulointerstitium showed “storiform” pattern with interstitial infiltration of IgG3 predominant plasma cells. Immunofluorescence showed linear and granular staining of IgG and C1q along TBM and interstitium. He started on medium dose of oral steroids and mycophenolate mofetil, which were gradually tapered. As a result, his renal function improved over a few days. Now, he continued on low dose steroids and mycophenolate mofetil with no evidence of relapse.

Renal Involvement in IgG4-Related Disease: From Sunlight to Twilight

IgG4-Related Disease (IgG4-RD) is a fibroinflammatory condition characterized by a typical histopathological pattern (dense lymphoplasmacytic infiltrate with prevalent IgG4+ plasma cells and storiform fibrosis), which may involve the kidney both directly (IgG4-related kidney disease, IgG4-RKD) or indirectly, as a consequence of post-renal ureteral obstruction due to retroperitoneal fibrosis (IgG4-RD RF). The most frequent presentation of IgG4-RKD is IgG4-related tubulointerstitial nephritis (TIN), but a glomerular disease can be present, in most of the cases a membranous nephropathy. Albeit steroid-responsive, in some cases renal manifestations may lead to progressive and permanent organ damage. In this review we describe four clinical cases representative of typical and less typical renal manifestations of IgG4-RD, emphasizing a potential, subclinical, early involvement of the kidney in the disease.

Tertiary lymphoid tissue in early-stage IgG4-related tubulointerstitial nephritis incidentally detected with a tumor lesion of the ureteropelvic junction: a case report

Background

IgG4-related kidney disease causes renal impairment of unknown pathogenesis that may progress to kidney failure. Although ectopic germinal centers contribute to the pathogenesis of the head and neck lesions of IgG4-related disease, the presence of tertiary lymphoid tissue (TLT) containing germinal centers in IgG4-RKD has rarely been reported.

Case presentation

We report a 72-year-old Japanese man who had IgG4-related tubulointerstitial nephritis (TIN) with TLT formation incidentally detected in a resected kidney with mass lesion of IgG4-related ureteritis in the ureteropelvic junction. During follow-up for past surgical resection of a bladder tumor, renal dysfunction developed and a ureter mass was found in the right ureteropelvic junction, which was treated by nephroureterectomy after chemotherapy. Pathology revealed no malignancy but abundant IgG4-positive cell infiltration, obliterative phlebitis and storiform fibrosis, confirming the diagnosis of IgG4-related ureteritis. In the resected right kidney, lymphoplasmacytes infiltrated the interstitium with focal distribution in the renal subcapsule and around medium vessels without storiform fibrosis, suggesting the very early stage of IgG4-TIN. Lymphocyte aggregates were also detected at these sites and consisted of B, T, and follicular dendritic cells, indicating TLT formation. IgG4-positive cells infiltrated around TLTs.

Conclusions

Our case suggests that TLT formation is related with the development of IgG4-TIN and our analysis of distribution of TLT have possibility to elucidate IgG4-TIN pathophysiology.

Validation of the diagnostic criteria for IgG4-related kidney disease (IgG4-RKD) 2011, and proposal of a new 2020 version

Background

In 2011, the IgG4-related kidney disease (IgG4-RKD) working group of the Japanese Society of Nephrology proposed diagnostic criteria for IgG4-RKD. The aim of the present study was to validate those criteria and develop a revised version.

Methods

Between April 2012 and May 2019, we retrospectively collected Japanese patients with kidney disease, for whom data on serum IgG4 values and/or immunohistological staining for IgG4 in renal biopsy samples were available. These patients were classified as IgG4-RKD or non-IgG4-RKD based on the diagnostic criteria for IgG4-RKD 2011, and the results were evaluated by expert opinion. Accordingly, we developed some revised versions of the criteria, and the version showing the best performance in the present cohort was proposed as the IgG4-RKD criteria for 2020.

Results

Of 105 included patients, the expert panel diagnosed 55 as having true IgG4-RKD and 50 as mimickers. The diagnostic criteria for IgG4-RKD 2011 had a sensitivity of 72.7% and a specificity of 90.0% in this cohort. Of the 15 patients with true IgG4-RKD who were classified as non-IgG4-RKD, all lacked biopsy-proven extra-renal lesions, although many had clinical findings highly suggestive of IgG4-RD. The revised version to which “bilateral lacrimal, submandibular or parotid swelling, imaging findings compatible with type 1 autoimmune pancreatitis or retroperitoneal fibrosis” was added as an item pertaining to extra-renal organ(s) improved the sensitivity to 90.9% while the specificity remained at 90.0%.

Conclusion

The revised version has considerably improved test performance after addition of the new extra-renal organ item (imaging and clinical findings).

IgG4 tubulointerstitial nephritis - An uncommon enemy!

IgG4-related disease (IgG4-RD) is an evolving entity characterized by immune mediated multisystem involvement in the form of fibro inflammatory lesions like sclerosing pancreatitis, dacryoadenitis, Reidel thyroiditis, or chronic sclerosing sialadenitis. Barely, the lesions are restricted to kidney (IgG4-RKD: IgG4-related kidney disease) involving either glomerular or extraglomerular compartment. It is challenging to identify and demands an awareness regarding the entity to reduce the number misdiagnosis and missed diagnosis. Here, we report a case of a 45-year-old woman with IgG4 tubulointerstitial nephritis (IgG4-TIN) who presented with unexplained renal dysfunction as her initial manifestation. This is the first case of IgG4-RKD reported from our tertiary care center among 1864 native renal biopsy in the last two years.

IgG4-related disease: a clinical perspective

IgG4-related disease (IgG4-RD) is a recently recognized fibro-inflammatory disorder that can affect almost any organ. Common presentations include major salivary and lacrimal gland enlargement, orbital disease, autoimmune pancreatitis, retroperitoneal fibrosis and tubulointerstitial nephritis. The main histopathological features are a dense, polyclonal, lymphoplasmacytic infiltrate rich in IgG4+ plasma cells, storiform fibrosis and obliterative phlebitis. The precise pathogenic mechanisms of IgG4-RD are still unclear. CD4+ T and B cells, including IgG4-expressing plasmablasts, constitute the major inflammatory cell populations and are believed to cause organ damage and tissue fibrosis. The diagnosis of the disease may be challenging and should be based on specific histopathological findings, typical laboratory and radiological aspects and an appropriate clinical context. The first-line treatment of IgG4-RD is based on glucocorticoids, which are usually efficacious. However, B cell depletion induced by rituximab has also been found to induce remission in steroid-resistant disease or has been used as steroid-sparing agent for relapsing disease. This review provides an update on clinical and therapeutic aspects of IgG4-RD.

Renal involvement in IgG4-related disease

IgG4-RD may affect several organs including kidneys. The kidney is involved in approximately 20% of patient with IgG4-RD. The most common intrinsic kidney disease is tubulointerstitial nephritis (IgG4-TIN). Retroperitoneal fibrosis (IgG4-RPF) may induce obstructive acute renal failure. More rarely, IgG4-RKD can manifest as a glomerular disease, in particular as a membranous nephropathy (MN). It mostly affects middle-aged to elderly men and causes acute or chronic renal dysfunction, multiple hypodense lesions on CT-Scan and various extra-renal lesions. Increased serum IgG4 and hypocomplementemia are the most important serological findings for the diagnosis of IgG4-RD and thus should be systematically assessed when IgG4-RKD is suspected. Specific diagnosis criteria for IgG4-TIN including interstitial infiltration of IgG4-positive plasma cells, storiform fibrosis and tubular basement membrane immune complex deposits have been proposed. Corticosteroids are effective and remain the first-line therapy but relapses or severe forms could respond to immunosuppressive therapy.

Renal tubular acidosis as the initial presentation of Sjögren's syndrome

We present a 44-year-old female with an initial presentation with distal renal tubular acidosis (RTA) after she presented with hypokalaemia and normal anion gap acidosis. Three years following the diagnosis, she presented with progressive renal impairment. In the absence of any clinical, biochemical and radiological clues, she underwent a renal biopsy which showed severe tubulitis secondary to lymphocytic infiltration. Serological investigations subsequently revealed positive anti-nuclear, anti-Sjögren’s syndrome related antigen A (SS-A), and anti-Sjögren’s syndrome related antigen B (SS-B) antibodies, supporting the diagnosis of Sjögren’s syndrome. This case is unique in that distal RTA was the presenting clinical manifestation of Sjögren’s syndrome. We hope that a consideration for Sjögren’s syndrome is made in patients with seemingly idiopathic RTA.

No overlap between IgG4-related disease and microscopic polyangiitis and granulomatosis with polyangiitis despite elevated serum IgG4 at diagnosis: a retrospective monocentric study

OBJECTIVES

We investigated whether elevated serum IgG4 at the time of diagnosis of microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA) may be associated with concurrent IgG4-related disease (IgG4-RD) in immunosuppressive drug-naïve patients.

METHODS

We retrospectively reviewed the medical records of 46 MPA and GPA patients with results on serum IgG4 and histology at diagnosis. Elevated serum IgG4 was defined as IgG4 > 135 mg/dL. We collected clinical and laboratory data at diagnosis including ANCA, white blood cell (WBC) count, haemoglobin, platelet, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and serum IgG4, and calculated Birmingham vasculitis activity score (BVAS) at diagnosis. We compared variables between patients with MPA and GPA and assessed the correlation of serum IgG4 and other continuous variables.

RESULTS

Twenty-eight patients (60.9%) were classified as MPA and 18 patients (39.1%) as GPA. The mean age at diagnosis was 61.0 years and 17 patients (37.0%) were men. The serum IgG4 at diagnosis was 1202.7 mg/dL and 37 patients (80.4%) had elevated serum IgG4 at diagnosis. We found no patients, who could be classified as IgG4-RD according to comprehensive diagnostic criteria for IgG4-RD among 46 patients. The mean serum IgG at diagnosis was not different between the two groups. Serum IgG4 was significantly correlated with inflammation-related variables at diagnosis including BVAS (r = 0.367), platelet (r = 0.398), ESR (r = 0.327), and CRP (r = 0.373).

CONCLUSIONS

Elevated serum IgG4 is not associated with concurrent IgG4-RD, and it may reflect activity and inflammatory burden of vasculitis in patients with MPA and GPA at diagnosis.

The Clinicopathologic Spectrum of IgG4-Related Disease

Immunoglobulin G4-related disease is a fibroinflammatory systemic disease that is characterized by focal or diffuse organ infiltration by immunoglobulin G4-bearing plasma cells. Immunoglobulin G4-related disease may affect any organ, and a high index of suspicion is necessary for early detection to avoid irreversible fibrosis, organ dysfunction, and death. Tumor-forming lesions are common radiological features of immunoglobulin G4-related disease that need to be differentiated from malignancies. The diagnostic approach requires the integration of clinical, biochemical, and radiographic manifestations with classic histopathologic features, which remain crucial to diagnosis. The histology of immunoglobulin G4-related disease is determined by a dense lymphoplasmacytic infiltrate, storiform fibrosis, and obliterative phlebitis in the presence of increased immunoglobulin G4-positve plasma cells. Although immunoglobulin G4-related disease forms a distinct, clinically independent disease category, many questions and problems remain unanswered, especially on its pathogenesis and the role of immunoglobulin G4. Advances in the understanding of immunoglobulin G4-related disease are likely to change the diagnostic approach in the future and create potential targets for therapeutic purposes. Here we describe the concept of immunoglobulin G4-related disease and the most recent knowledge in the clinico-pathological characteristics on this emerging disease. This study can guide clinicians in early diagnosis and prevent unnecessary surgical resections.

Immunoglobulin G4-related kidney diseases: An updated review

This review will encompass definition, pathogenesis, renal clinical manifestations and treatment of immunoglobulin G4-related diseases (IgG4-RDs). IgG4-RD is a recently recognized clinical entity that often involves multiple organs and is characterized by high levels of serum immunoglobulins G4, dense infiltration of IgG4+ cells and storiform fibrosis. Cellular immunity, particularly T-cell mediated immunity, has been implicated in the pathogenesis of IgG4-RDs. The most frequent renal manifestations of IgG4-RD are IgG4-related tubulointerstitial nephritis, membranous glomerulopathy and obstructive nephropathy secondary to urinary tract obstruction due to IgG4-related retroperitoneal fibrosis. IgG4-RD diagnosis should be based on specific histopathological findings, confirmed by tissue immunostaining, typical radiological findings and an appropriate clinical context. The first line treatment is the steroids with two warnings: Steroid resistance and relapse after discontinuation. In the case of steroid resistance, B cell depleting agents as rituximab represent the second-line treatment. In the case of relapse after discontinuation, steroid treatment may be associated with steroid sparing agents. Since the disease has been only recently identified, more prospective, long-term studies are needed to an improved understanding and a more correct and safe treatment.

Successful treatment of highly advanced immunoglobulin G4-related kidney disease presenting renal mass-like regions with end-stage kidney failure: a case study

Background

Immunoglobulin G4-related kidney disease characterized by immunoglobulin G4-positive plasma cell-rich tubulointerstitial nephritis has distinctive serological and radiological findings. Renal prognosis is good because of a good response to glucocorticoids. Here we report a case of successful treatment of highly advanced immunoglobulin G4-related kidney disease presenting renal mass-like regions with end-stage kidney failure.

Case Presentation

A 59-year-old Japanese man was referred to our hospital because of uremia with a creatinine level of 12.36 mg/dL. Urinalysis revealed mild proteinuria and hyperβ2microglobulinuria, and blood tests showed hyperglobulinemia with an IgG level of 3243 mg/dL and an IgG4 level of 621 mg/dL. Non-contrast computed tomography revealed renal mass-like regions. Based on the findings, immunoglobulin G4-related kidney disease was suspected, however, further radiological examination showed unexpected results. Ga-67 scintigraphy showed no kidney uptake. T2-weighted magnetic resonance imaging revealed high-intensity signals which corresponded to mass-like regions and multiple patchy low-intensity signals in kidney cortex. Finally, the patient was diagnosed with immunoglobulin G4-related kidney disease by renal pathology of severe immunoglobulin G4-positive plasma cell-rich tubulointerstitial nephritis and characteristic fibrosis. He received 50 mg oral prednisolone, which was tapered with a subsequent decrease of serum creatinine and IgG4 levels. One year after initiation of treatment, he achieved normalization of serum IgG4 level and proteinuria, and remained off dialysis with a creatinine level of 3.50 mg/dL. After treatment with steroids, repeat imaging suggested bilateral severe focal atrophy. However, mass-like regions did not show atrophic change although renal atrophy was evident in patchy low-intensity lesions on T2-weighted magnetic resonance imaging. These findings suggest that multiple patchy low-intensity signals and high-intensity mass-like regions were mildly atrophic lesions of immunoglobulin G4-related kidney disease due to severe fibrosis and normal parts of kidney, respectively.

Conclusions

In immunoglobulin G4-related kidney disease with severe kidney failure, radiological findings should be carefully examined. In addition, renal prognosis may be good despite highly advanced tubulointerstitial nephritis and fibrosis.

Immunoglobulin G4-related kidney disease: Pathogenesis, diagnosis, and treatment

Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized clinical entity that often involves multiple organs; it is characterized by high levels of serum immunoglobulin G4 (IgG4), dense infiltration of IgG4+ cells, and storiform fibrosis. Cellular immunity, particularly T cell-mediated immunity, has been implicated in the pathogenesis of IgG4-RD. The most frequent renal manifestations of IgG4-RD are IgG4-related tubulointerstitial nephritis, membranous glomerulonephropathy (MGN), and obstructive nephropathy secondary to urinary tract obstruction due to IgG4-related retroperitoneal fibrosis, prostatitis, or ureter inflammation. Kidney function impairment can be acute or chronic. In IgG4-MGN, proteinuria can be in the nephrotic range. The diagnosis of IgG4-related kidney disease should not be based solely on serum IgG4 levels or the number of tissue-infiltrating IgG4+ plasma cells. Diagnosis should be based on specific histopathological findings, confirmed by tissue immunostaining and an appropriate clinical context. Steroid treatment is the first-line therapy. For relapsing or refractory cases, immunosuppressants could be combined with steroids. In hydronephrosis patients, appropriate immunosuppressive therapy could preclude the implantation of a double J ureteral catheter.

A condition closely mimicking IgG4-related disease despite the absence of serum IgG4 elevation and IgG4-positive plasma cell infiltration

We describe a 74-year-old Japanese man with systemic fibroinflammatory conditions closely resembling those of immunoglobulin G4-related disease (IgG4-RD). Radiology and histology showed characteristics of IgG4-related tubulointerstitial nephritis, despite normal serum IgG4 value and scanty IgG4-positive plasma cell infiltration in each organ. This case suggests that a condition closely mimicking IgG4-RD may develop without IgG4-positive plasma cells and those exceptional cases should also be taken into account in the differential diagnosis of IgG4-RD.

Factors related to renal cortical atrophy development after glucocorticoid therapy in IgG4-related kidney disease: a retrospective multicenter study

Background

In immunoglobulin G4-related kidney disease (IgG4-RKD), focal or diffuse renal cortical atrophy is often observed in the clinical course after glucocorticoid therapy. This study aimed to clarify the factors related to renal atrophy after glucocorticoid therapy in IgG4-RKD.

Methods

We retrospectively evaluated clinical features including laboratory data and computed tomography (CT) findings before and after glucocorticoid therapy in 23 patients diagnosed with IgG4-RKD, all of whom were followed up for more than 24 months.

Results

Seventeen patients were men, and six were women (average age 62.0 years). Average follow-up period was 54.9 months. The average estimated glomerular filtration rate (eGFR) at diagnosis was 81.7 mL/min/1.73 m². All patients had had multiple low-density lesions on contrast-enhanced CT before glucocorticoid therapy, and showed disappearance or reduction of these lesions after it. Pre-treatment eGFR and serum IgE level in 11 patients in whom renal cortical atrophy developed 24 months after the start of glucocorticoid therapy were significantly different from those in 12 patients in whom no obvious atrophy was found at that time (68.9 ± 30.1 vs 93.5 ± 14.1 mL/min/1.73 m², P = 0.036, and 587 ± 254 vs 284 ± 263 IU/mL, P = 0.008, respectively). Pre-treatment eGFR and serum IgE level were also significant risk factors for renal atrophy development 24 months after the start of therapy with an odds ratio of 0.520 (per 10 mL/min/1.73 m², 95% confidence interval (CI) 0.273–0.993, P = 0.048) and 1.090 (per 10 IU/mL, 95% CI: 1.013–1.174, P = 0.022), respectively, in age-adjusted, sex-adjusted, serum IgG4 level-adjusted logistic regression analysis. Receiver operating characteristic curve analysis showed that eGFR of less than 71.0 mL/min/1.73 m² and serum IgE of more than 436.5 IU/mL were the most appropriate cutoffs and yielded sensitivity of 63.6% and specificity of 100%, and sensitivity of 90.9% and specificity of 75.0%, respectively, in predicting renal atrophy development.

Conclusions

This study suggests that pre-treatment renal insufficiency and serum IgE elevation predict renal atrophy development after glucocorticoid therapy in IgG4-RKD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1175-y) contains supplementary material, which is available to authorized users.

Multicentric Castleman Disease With Tubulointerstitial Nephritis Mimicking IgG4-related Disease: Two Case Reports

Multicentric Castleman disease is a benign lymphoproliferative disorder with heterogenous clinical symptoms and involves systemic organs in addition to lymph nodes. Elevated serum IgG4 levels and IgG4-positive plasma cell (IgG4+PC) infiltrates have been reported in lymph nodes, lung and skin in some multicentric Castleman disease cases, resembling IgG4-related disease (IgG4-RD) histologically. However, no report has been available regarding IgG4+PC infiltration in the kidneys of multicentric Castleman disease. Here, we report 2 cases of multicentric Castleman disease complicated by IgG4-related disease (IgG4-RD) histologically. However, there has been no report published on PC-rich tubulointerstitial nephritis, lymphadenopathy, with numerous IgG4+PC infiltration, and elevated serum IgG4 levels, mimicking IgG4-RD. The blood examinations revealed systemic inflammation and elevated C-reactive protein and interleukin-6 levels. Corticosteroid therapy was partially effective in both cases, and combination therapy of corticosteroid and tocilizumab was needed in both cases. Moreover, after triple therapy with corticosteroid, rituximab and cyclophosphamide were used in 1 case to tame the severe inflammation. The present cases suggest that if continuously elevated serum C-reactive protein levels and partial corticosteroid responsiveness are encountered, multicentric Castleman disease should be considered rather than IgG4-RD as a differential diagnosis even if serum IgG4 is elevated and IgG4+PCs infiltrate systemic organs.

Distribution and components of interstitial inflammation and fibrosis in IgG4-related kidney disease: analysis of autopsy specimens

IgG4-related kidney disease (IgG4-RKD) occasionally progresses to chronic renal failure and is pathologically characterized by IgG4-positive lymphoplasmacyte-rich tubulointerstitial nephritis with storiform fibrosis (bird's-eye pattern fibrosis). Although radiology reveals a heterogeneous distribution of affected areas in this disease, their true distribution within the whole kidney is still unknown because of difficulty in estimating this from needle biopsy samples. Using 5 autopsy specimens, the present study histologically characterized the distribution and components of interstitial inflammation and fibrosis in IgG4-RKD. Interstitial lymphoplasmacytic infiltration or fibrosis was observed in a variety of anatomical locations such as intracapsular, subcapsular, cortical, perivascular, and perineural regions heterogeneously in a patchy distribution. They tended to be more markedly accumulated around medium- and small-sized vessels. Storiform fibrosis was limited to the cortex. Immunostaining revealed nonfibrillar collagens (collagen IV and VI) and fibronectin predominance in the cortical lesion, including storiform fibrosis. In contrast, fibril-forming collagens (collagen I and III), collagen VI, and fibronectin were the main components in the perivascular lesion. In addition, α-smooth muscle actin-positive myofibroblasts were prominently accumulated in the early lesion and decreased with progression, suggesting that myofibroblasts produce extracellular matrices forming a peculiar fibrosis. In conclusion, perivascular inflammation or fibrosis of medium- and small-sized vessels is a newly identified pathologic feature of IgG4-RKD. Because storiform fibrosis contains mainly nonfibrillar collagens, "interstitial fibrosclerosis" would be a suitable term to reflect this. The relation between the location and components of fibrosis determined in whole kidney samples provides new clues to the pathophysiology underlying IgG4-RKD.

Recovery of renal function after glucocorticoid therapy for IgG4-related kidney disease with renal dysfunction

BACKGROUND

Although renal dysfunction in IgG4-related kidney disease (IgG4-RKD) shows rapid resolution with glucocorticoid therapy, little is known about the appropriate initial glucocorticoid dose for induction therapy or long-term renal outcome.

METHODS

We retrospectively examined the differences in recovery of renal function according to the dose of glucocorticoid used for induction therapy and the long-term renal outcome in 43 patients with definite IgG4-RKD (mostly IgG4-tubulointerstitial nephritis), in whom the estimated glomerular filtration rate (eGFR) before glucocorticoid therapy was <60 ml/min.

RESULTS

Most patients were treated with glucocorticoid alone and had been maintained on glucocorticoid. The initial dose of prednisolone employed was ≤0.6 mg/kg/day (mean 0.47) in 27 patients (group L), and >0.6 mg/kg/day (mean 0.81) in 16 patients (group H). In both groups, the pretreatment eGFR was significantly improved at 1 month after the start of glucocorticoid therapy and the degree of improvement showed no significant inter-group difference. Relapse of IgG4-RKD occurred in 16.7% of the group L patients and 13.3% of the group H patients (p = 0.78). Among 29 patients who were followed up for over 36 months (mean 74 months) and had been maintained on glucocorticoid, none showed progression to end-stage renal disease and there was no significant difference between eGFR at 1 month after treatment and eGFR at the last review.

CONCLUSION

In glucocorticoid monotherapy for IgG4-RKD, a moderate dose is sufficient for induction, and recovery of renal function can be maintained for a long period on low-dose maintenance, although relapse can occur even in patients receiving maintenance therapy.

IgG4-related disease: A relatively new concept for clinicians

IgG4-related disease (IgG4-RD) is a recently recognized chronic fibrotic inflammation, which can affect almost every organ, and may come to clinical attention first due to visible organ swelling or organ dysfunction, or is identified incidentally by imaging and specific biopsy. The disorder has an allergic background and is immune-mediated. Up-regulated responses of T helper 2 and T regulatory cells and their cytokines play a major role in disease progression. About 30-50% of patients are atopic or have mild eosinophilia. IgG4-RD predominantly affects middle-aged male patients. The cornerstones of diagnosis of the disease are compatible clinical features and typical histopathology. Swelling of salivary and lacrimal glands, lymphadenopathy, and type 1 autoimmune pancreatitis (AIP) are the most common manifestations of the disease. However, other tissues and organs, such as retroperitoneum, lung, kidney, aorta, upper airways, thyroid gland, meninges, heart, mesenterium and skin may be involved. Typical histopathology is lymphoplasmacytic infiltration abundant in IgG4-positive plasma cells, storiform-type fibrosis, and obliterative phlebitis. Elevated serum IgG4 concentration supports the diagnosis. Characteristic imaging features such as a "capsule-like rim" surrounding the pancreatic lesions is highly specific to type 1 AIP. 18F-fluorodeoxyglucose positron emission tomography/computed tomography enables mapping the sites of inflammation, permits evaluation of the extent of the disease, helps in guiding biopsy decision, and may be used in monitoring response to treatment. Glucocorticoids alone or in combination with B-cell depletion with rituximab induces prompt clinical response to IgG4-RD. This article reviews the current understanding, different clinical manifestations, and approaches to diagnosis and treatment of IgG4-RD.

Overview of IgG4-Related Tubulointerstitial Nephritis and Its Mimickers

Tubulointerstitial nephritis (TIN) is the most common form of renal involvement in IgG4-related disease. It is characterized by a dominant infiltrate of IgG4-positive plasma cells in the interstitium and storiform fibrosis. Demonstration of IgG4-positive plasma cells is essential for diagnosis, but the number of IgG4-positive cells and the ratio of IgG4-positive/IgG-positive plasma cells may vary from case to case and depending on the methods of tissue sampling even in the same case. IgG4-positive plasma cells can be seen in TIN associated with systemic lupus erythematosus, Sjögren syndrome, or anti-neutrophil cytoplasmic antibody–associated vasculitis, which further add diagnostic confusion and difficulties. To have a more clear view of IgG4-TIN and to delineate differential points from other TIN with IgG4-positive plasma cell infiltrates, clinical and histological features of IgG4-TIN and its mimickers were reviewed. In the rear part, cases suggesting overlap of IgG4-TIN and its mimickers and glomerulonephritis associated with IgG4-TIN were briefly described.

IgG4-related kidney disease--an update

Purpose of review

IgG4-related disease (IgG4-RD) is a recently recognized systemic inflammatory disorder that can affect most organs/tissues such as sarcoidosis. The kidney is a frequently affected organ with tubulointerstitial nephritis (TIN), the representative lesion of IgG4-RD. This review focuses on the latest knowledge of IgG4-related kidney disease (IgG4-RKD).

Recent findings

A wide range of renal manifestations of IgG4-RD, that is TIN, membranous glomerulonephritis (MGN) and other glomerular lesions, and pyelitis, are collectively referred to as IgG4-RKD. Clinically, decreased renal function, or characteristic imaging findings such as multiple low-density lesions on contrast-enhanced computed tomography or diffuse thickening of the renal pelvic wall, are typical presenting features. Although a rapid response to corticosteroid therapy is a very important feature of IgG4-TIN, in cases in which renal function is moderately to severely decreased before therapy, only partial recovery of renal function is obtained.

Summary

TIN with characteristic imaging findings is a typical manifestation of IgG4-RKD in the interstitium, while MGN is a representative manifestation of the glomerular lesions. Although IgG4 is a central feature of IgG4-RD, the recent discovery of IgG4-negative IgG4-RD raises questions about the causative role of the IgG4 molecule in this context.

Etiological diagnosis of granulomatous tubulointerstitial nephritis in the tropics

BACKGROUND

Granulomatous tubulointerstitial nephritis (GIN) is common due to infections, drugs or sarcoidosis. However, the cause is often difficult to establish and the studies are limited. We studied the etiology of GIN and compared the clinical and histological features and outcome in different etiologies at a tertiary care center in North India.

METHODS

Renaö biopsies from GIN cases diagnosed from January 2004 to April 2014 were retrieved. Stain for acid fast bacilli was performed in all biopsies. Etiological diagnosis was based on clinical features, extra-renal manifestations, radiology, history of drug intake and demonstration of infective agent. Tissue PCR for tubercular DNA was performed in seven biopsies.

RESULTS

Seventeen GIN patients [mean age 35 ± 15 years; males 11] were identified. Tuberculosis was the commonest etiology followed by idiopathic, sarcoidosis and fungal. Both tuberculosis and sarcoidosis patients presented with subnephrotic proteinuria and raised serum creatinine. Acid fast bacilli were demonstrated in 1/9 and necrosis was demonstrated in 3/9 granulomas in tuberculosis. Tissue PCR for tubercular DNA was positive in six TB patients and negative in one sarcoidosis patient. Patients responded well to appropriate therapy.

CONCLUSION

Etiological diagnosis of GIN is essential for timely and appropriate therapy. Tuberculosis is the commonest etiology (53%) in the tropics. Necrosis in granuloma, demonstration of acid fast bacilli, blood interferon gamma release assay and urine culture is not sensitive for the diagnosis of tuberculosis in GIN. Our findings suggest that tissue PCR for tuberculosis performed in an appropriate clinical setting is useful in the diagnostic evaluation of GIN.

Evaluation of diagnostic criteria for IgG4-related tubulointerstitial nephritis

Background

IgG4-TIN is the most common pattern of renal involvement in IgG4-related disease. There are several proposed diagnostic criteria of IgG4-TIN recently. Two of them proposed by the Mayo Clinic and JSN are predominant. However, histopathological criteria of the number of IgG4+ plasma cells and several histological features are still under discussion due to low amount of tissue in renal biopsy specimens and low frequency of this kind of specimens. We aimed to screen IgG4-TIN on archived renal biopsy samples and evaluated the application of two proposed diagnostic criteria.

Methods

We selected 480 interstitial inflammation samples for light and electron microscopy and immunohistochemistry of CD138, IgG and IgG4 test. The Mayo Clinic proposed criteria diagnosed high-probability IgG4-TIN and JSN criteria confirmed IgG4-TIN.

Results

Twelve high-probability IgG4-TIN were screened by histology, imaging, serology and other organ involvement according to the Mayo Clinic proposed criteria. The previous principal pathological diagnoses were IgAN (n=4), CreGN (n=4), tubulointerstitial nephritis (n=3) and LN (n=1). Three cases showed storiform fibrosis and a bird’s eye pattern. The distribution of IgG4+ plasma cells was focal, multifocal or diffuse, with a mixed mild, moderate or strong stainingpattern. Their treatment and clinical outcomes varied depending on different levels of proteinuria, serum creatinine, eGFR and original glomerular disease presentation. Therefore, we applied strict histological criteria of storiform fibrosis and evenly distributed IgG4+ plasma cells by JSN to confirm typical IgG4-TIN. Two cases were finally diagnosed as real IgG4-TIN. One was previously diagnosed as idiopathic interstitial nephritis with rapid response to corticosteroid therapy. The other was CreGN with immune complex deposits, which had poor outcome and long-term hemodialysis.

Conclusions

IgG4-TIN might present concurrently with glomerular disease. The proposed criteria by the Mayo Clinic is flexible, sensitive, and superior in the identification of early-stage or atypical IgG4-TIN, with enhanced risk of misdiagnosis as compared to the proposed criteria by JSN, which is stricter, more specific, and might overlook early-stage or atypical IgG4-TIN. We propose a new set of criteria to improve pathologist-derived diagnosis.

Immunoglobulin G4-related tubulointerstitial nephritis associated with interstitial pulmonary disease: Report of a case with review of literature

Immunoglobulin G4-related disease (IgG4-RD) is an emerging clinicopathological entity. Renal involvement is dominated by tubulointerstitial nephritis (TIN) with IgG4-positive plasma cells and fibrosis. IgG4-RD commonly affects middle-aged to elderly men with accompanying extra-renal lesions such as sialadenitis, lymphadenopathy, or type 1 autoimmune pancreatitis, all of which respond favorably to corticosteroid therapy. The disease burden of IgG4-related kidney disease (IgG4-RKD) in India remains largely underestimated. We report a case of IgG4-RKD manifesting as TIN associated with interstitial pulmonary disease, illustrating typical clinico-pathologic, serologic, immuno-histochemical, and ultrastructural features of this condition. In view of potential amelioration of renal dysfunction with appropriate therapy, the need for awareness of this condition and early diagnosis is highlighted.

A case of IgG4-positive plasma cell-rich tubulointerstitial nephritis in a kidney allograft mimicking IgG4-related kidney disease

A 51-year-old woman received an ABO blood type-incompatible renal transplant. She was administered rituximab and basiliximab and underwent plasma exchanges for induction therapy, followed by administration of tacrolimus, mycophenolate mofetil and methylprednisolone as maintenance immunosupression therapy. A planned renal biopsy 2 years after transplantation revealed infiltration of plasma cells in the renal interstitium, although there was no 'storiform' fibrosis surrounding these cells. There were also no findings of rejection, BK virus nephropathy, or atypical plasma cells. Immunohistochemical stainings showed a large number of IgG4-positive plasma cells, most of which expressed kappa-type light chains. A CT scan showed a mass at the renal hilum. The serum IgG4 level was high. Based on these findings, the patient was suspected of having IgG4-related kidney disease. Nine months after the biopsy, her serum creatinine level increase to 1.56 mg/dL and the dose of methylprednisolone was therefore increased to 16 mg/day. Three months after this increase in steroid, a CT scan showed the hilum mass had disappeared. A follow-up biopsy 5 months later showed that infiltration of plasma cells in the renal interstitium had decreased markedly, although focal and segmental severely fibrotic lesions with IgG4-positive plasma cells were observed. Serum IgG4 levels decreased immediately after the increase in steroid dose and remained <100 mg/dL despite a reduction in methylprednisolone to 6 mg/day. Serum creatinine levels also remained stable at around 1.6 mg/dL. To our knowledge, this is the first report of IgG4-positive plasma cell-rich tubulointerstitial nephritis mimicking IgG4-related kidney disease after kidney transplantation.

Ultrastructural studies of IgG4-related kidney disease

OBJECTIVE

Ultrastructural studies of IgG4-related kidney disease (IgG4-RKD) characterized by tubulointerstitial nephritis (TIN) are limited in previous reports due to the rarity of the condition. In the present report, we performed ultrastructural examinations and assessed the pathogenesis of this disease.

PATIENTS

Clinicopathological studies were conducted in eight patients diagnosed with IgG4-RKD. Routine light, immunofluorescence and electron microscopy examinations and immunohistochemical assessments of IgG4 were performed using renal biopsy samples.

RESULTS

Hypocomplementemia, positive anti-nuclear antibodies and eosinophilia were confirmed in more than half of the cases. Electron dense deposits (EDDs) were frequently found in the glomeruli and interstitium. The rate of deposition was 62.5% in both mesangial areas and Bowman's capsule. EDDs were frequently detected on the tubular basement membrane (TBM) (87.5% of patients). The interstitium also contained EDDs on collagen fibers in 87.5% of the cases and on basement membrane-like materials in areas of fibrosis in 37.5% of the cases. The creatinine clearance levels were significantly lower in the patients with the latter pattern. Meanwhile, the rate of immunoglobulin and/or complement deposition on the TBM was observed in less than 37.5% of patients, and these findings were not entirely coincident with the cases of EDDs on the TBM.

CONCLUSION

EDDs are frequently found in the glomeruli and interstitium in patients with IgG4-RKD; however, immunohistological studies do not provide evidence that IgG4-RKD involves TIN with immune complex nephropathy. The presence of interstitial EDDs may be related to the progression of interstitial fibrosis in the setting of IgG4-RKD.

The clinical spectrum of IgG4-related disease

IgG4-related disease (IgG4-RD) is an emerging immune-mediated disease with the capability of involving essentially any organ. The epidemiology of this disease has not been explored in detail. A majority of patients reported in the literature to date are from Japan, but the condition has been described all across the world and there is no strong evidence to suggest a predilection for Asian populations. The mean age at diagnosis is approximately 60 years and there is a decided male predominance for many clinical features, with an overall male:female ratio of 8:3. A cardinal feature of IgG4-RD is single or multiple organ swelling that often raises concern for malignancy. IgG4-RD should be suspected in patients presenting with unexplained enlargement or swelling of one or more organs. Presenting features vary substantially according to the specialty to which patients present first; in addition, the disease can be diagnosed unexpectedly in pathological specimens or identified incidentally on radiology studies. Involvement of major organs is common and IgG4-RD may lead to organ failure, particularly in the pancreas, liver and biliary tree, kidneys, thyroid gland, lungs, and aorta. The diagnosis of IgG4-RD relies on the coexistence of various clinical, laboratory and histopathological findings, although none is pathognomonic by itself.

Clinical relevance of Küttner tumour and IgG4-related dacryoadenitis and sialoadenitis

Objectives

Küttner tumour (KT), so-called chronic sclerosing sialoadenitis, is characterised by concomitant swelling of the submandibular glands secondary to strong lymphocytic infiltration and fibrosis independent of sialolith formation. However, recent studies have indicated that some patients with KT develop high serum levels of IgG4 and infiltration of IgG4-positive plasma cells, namely IgG4-related dacryoadenitis and sialoadenitis (IgG4-DS), so-called Mikulicz's disease. The aim of this study was to clarify the clinical and pathological associations between KT and IgG4-DS.

Materials and Methods

Fifty-four patients pathologically diagnosed with KT or chronic sialoadenitis were divided into two groups according to the presence or absence of sialolith (KT-S (+) or KT-S (−), respectively).

Results

There were no significant differences in the clinical findings, including the mean age, sex and disease duration, between the two groups. All patients in the KT-S (+) group showed unilateral swelling without infiltration of IgG4-positive plasma cells or a history of other IgG4-related diseases (IgG4-RD), while those in the KT-S (−) group showed bilateral swelling (37.5%), strong infiltration of IgG4-positive plasma cells (87.5%) and a history of other IgG4-RD (12.5%).

Conclusions

These results suggest an association between the pathogeneses of KT-S (−) and IgG4-DS, but not KT-S (+).

A case of ANCA-negative renal small-vessel vasculitis with tubulointerstitial infiltration of IgG4-positive plasma cells

A 62-year-old male patient presented with progressive renal dysfunction for 2 months. He had elevated serum C-reactive protein and IgG4 levels with absence of anti-neutrophil cytoplasmic antibodies. A renal biopsy showed severe tubulointerstitial nephritis (TIN) with extensive infiltration of IgG4-positive plasma cells, suggesting a diagnosis of IgG4-related kidney disease (IgG4-RKD). However, the identification of a few crescentic glomeruli and necrotizing vasculitis of an interlobular artery lead to a diagnosis of renal small-vessel vasculitis. This case indicates that a careful examination is required to distinguish between IgG4-RKD and TIN caused by renal small-vessel vasculitis.

A Retrospectively Diagnosed Case of IgG4-Related Tubulointerstitial Nephritis Showing Good Renal Outcome and Pathological Progress

A 74-year-old man was hospitalized for diabetic nephropathy evaluation and assessment of the effect of treatment on his tubulointerstitial nephritis (TIN). When he was 62 years old, he developed polyarthralgia and had superficial lymph node swelling, mildly increased serum creatinine concentration, hypergammaglobulinemia, hypocomplementemia, high serum IL-2R level, and positive titer of antinuclear antibody. Several tissues were biopsied. Mild chronic sialadenitis and reactive lymphadenitis were identified. Renal specimen showed mild glomerular ischemia, extensive storiform fibrosis, and abundant infiltrating monocytes and plasma cells. He was treated with oral prednisolone and cyclophosphamide. After the treatment, most of his clinical parameters quickly returned to within the reference range. However, he developed diabetes mellitus soon after steroid therapy. At the time of rebiopsy, a high level of serum IgG4 was detected. The second renal biopsy showed diabetic nephropathy without any tubulointerstitial damage. The first biopsied tissues were retrospectively investigated. Large numbers of IgG4-positive plasma cells were detected in the kidneys and lymph nodes. A retrospective diagnosis of IgG4-related TIN with lymph node involvement was made. In conclusion, this paper describes a retrospectively diagnosed case of IgG4-related TIN with lymph node involvement, showing good clinical and pathological prognosis.

IgG4-related kidney disease

IgG4-related kidney disease (IgG4-RKD) is a comprehensive term for renal lesions associated with IgG4-related disease, which is a recently recognized clinical entity characterized by a dense lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells with fibrosis affecting several organs. Tubulointerstitial nephritis with increased IgG4-positive plasma cells and fibrosis is the most dominant feature of IgG4-RKD and may cause acute or chronic renal dysfunction, although some glomerular lesions such as membranous nephropathy are sometimes evident. Radiologically, several characteristic abnormalities are often demonstrated, sometimes mimicking malignancies. IgG4-RKD predominantly affects middle-aged to elderly men, and most patients have accompanying IgG4-related extrarenal lesions such as sialadenitis, lymphadenopathy, or type 1 autoimmune pancreatitis. Serology usually demonstrates high levels of serum total IgG and IgG4, and high levels of serum IgE and hypocomplementemia are also frequent features. Corticosteroid therapy is usually quite effective, leading to amelioration of the renal dysfunction and radiological and serological abnormalities. However, as any delay in treatment may result in irreversible renal failure, early diagnosis and appropriate therapy are very important. Despite these distinctive clinicopathological features of IgG4-RKD, its pathogenesis remains poorly understood. Awareness of this condition and accumulation of more cases worldwide are necessary.

The clinical course of patients with IgG4-related kidney disease

Long-term follow-up for IgG4-related kidney disease, including relapse information, is sparse. To gather data on this we retrospectively examined the clinical course of 43 patients with IgG4-related kidney disease, in which most patients were treated with, and maintained on, corticosteroids. One month after the start of treatment, most of the abnormal serology and radiology parameters had improved. In 34 of the steroid-treated patients whose follow-up period was more than 12 months (median 34 months), excluding one hemodialysis patient, the estimated glomerular filtration rate (eGFR) before treatment was over 60 ml/min in 14 patients (group A) and under 60 ml/min in 20 patients (group B). In group A, there was no difference between the eGFR before therapy and at the last review. In group B, the mean eGFR before treatment (34.1 ml/min) was significantly improved after 1 month (45.0 ml/min), and renal function was maintained at a similar level through last follow-up. Among 24 evaluated patients at the last review, however, renal atrophy had developed in 2 of 9 in group A and in 9 of 15 in group B. Relapse of IgG4-related lesions occurred in 8 of 40 treated patients. Thus, the response of IgG4-related kidney disease to corticosteroids is rapid, not total, and the recovery of renal function persists for a relatively long time under low-dose maintenance. A large-scale prospective study to formulate more useful treatment strategies is necessary.