Immunoglobulin G4-related kidney diseases: An updated review

Predominantly multiple focal non-cystic renal lesions: an imaging approach

Multiple non-cystic renal lesions are occasionally discovered during imaging for various reasons and poses a diagnostic challenge to the practicing radiologist. These lesions may appear as a primary or dominant imaging finding or may be an additional abnormality in the setting of multiorgan involvement. Awareness of the imaging appearance of the various entities presenting as renal lesions integrated with associated extrarenal imaging findings along with clinical information is crucial for a proper diagnostic approach and patient work-up. This review summarizes the most relevant causes of infectious, inflammatory, vascular, and neoplastic disorders presenting as predominantly multiple focal non-cystic lesions.

Presumed Choroidopathy of IgG4-Related Disease Discovered During 16-Year Follow-Up of a Patient With Polycystic Kidney Disease

Immunoglobulin G4 (IgG4)-related disease is characterized by infiltration with IgG4-producing plasma cells in different organs and the elevation of serum IgG4. We present a patient with polycystic kidney disease in long-term follow-up who developed bilateral lacrimal gland enlargement and presumed IgG4-related choroidopathy at different time points. A 45-year-old woman developed bilateral upper eyelid swelling. Head MRI showed bilateral lacrimal gland enlargement, and the resection on both sides revealed foci of infiltration with lymphocytes and plasma cells in bilateral lacrimal glands. The IgG4-immunostaining did not satisfy the diagnostic criteria. She had been taking oral valsartan 40 mg daily for hypertension with polycystic kidney disease. The patient was well until the age of 49 years, when she noticed yellowish vision in the right eye compared to the left eye. The right eye showed multiple yellowish spotty lesions in the deep retina to choroid with a mildly hyperemic optic disc, while the left eye showed the normal fundus. No inflammation was noted in the anterior segments of both eyes. Fundus angiography demonstrated early-phase no-filling with late-phase leakage by fluorescein dye and both early-phase and late-phase no-filling by indocyanine green dye, leading to the diagnosis of acute posterior multifocal placoid pigment epitheliopathy (APMPPE). She began to have oral prednisolone tapered from 30 mg daily and discontinued in a year. At the age of 52 years, she switched to candesartan 8 mg daily and began to have tolvaptan (a selective competitive vasopressin receptor 2 (V2) antagonist) 90 mg daily for polycystic kidney disease with liver cysts. At that time, the lesions in the right eye had mild degeneration. The patient was followed once a year ophthalmologically to maintain good vision. At 57 years, serum IgG4, which was measured for the first time on suspicion of IgG4-related disease, was elevated to 269.6 mg/dL. In the following four years to the latest visit at 61 years, she kept stable but high levels of serum IgG4 around 300 mg/dL. Serum IgG4 measurement is helpful to make a clinical diagnosis and, hence, a clinical decision since the spectrum of IgG4-related disease remains obscure.

IgG4-related disease: an update on pathology and diagnostic criteria with a focus on salivary gland manifestations

Immunoglobulin G4-related disease (IgG4-RD) is a multi-organ disorder characterized by a highly variable clinical presentation depending on the affected organ/s, extent of tumefactive fibroinflammatory lesions, and associated functional impairment. The disease pursues a chronic, relapsing, often asymptomatic course and hence may pose a significant diagnostic challenge. Diagnostic delay can lead to progressive fibrosis and irreversible organ damage resulting into significant morbidity and even mortality. Given its broad clinical spectrum, physicians of all specialties may be the first clinicians facing this diagnostic challenge. Outside the pancreatobiliary system, the head and neck represents the major site of IgG4-RD with variable organ-specific diffuse or mass-forming lesions. In up to 75% of cases, elevated serum IgG4 levels are observed, but this figure possibly underestimates the fraction of seronegative cases, as the disease manifestations may present metachronously with significant intervals. Together with negative serology, this can lead to misdiagnosis of seronegative cases. A standardized nomenclature and diagnostic criteria for IgG4-RD were established in 2012 and revised in 2020 facilitating scientific research and expanding the range of diseases associated with IgG4 abnormalities. In addition to orbital pseudotumor, dacryoadenitis, Riedel thyroiditis, sinonasal manifestations, and rare miscellaneous conditions, IgG4-related sialadenitis is one of the most frequent presentations in the head and neck region. However, controversy still exists regarding the relationship between sialadenitis and IgG4-RD. This review focuses on the clinicopathological features of IgG4-related sialadenitis and its contemporary diagnostic criteria.

A pictorial review of genitourinary infections and inflammations

Various infectious and inflammatory diseases affect the genitourinary system. This paper provides a review of multiple common and uncommon infectious and inflammatory conditions affecting the genitourinary system and some associated complications. These include acute infectious cystitis, emphysematous cystitis, acute pyelonephritis, emphysematous pyelonephritis, renal and perinephric abscesses, pyonephrosis, xanthogranulomatous pyelonephritis, epididymo-orchitis, vasitis, prostatitis, pelvic inflammatory disease, renal hydatid infection, renal tuberculosis, actinomycosis, Erdheim-Chester Disease, IgG4-Related Kidney Disease, urethritis and urethral strictures, ureteritis cystica, and genitourinary fistulas. Radiologists should be aware of these diseases' complications and management. Uncommon conditions must be considered when evaluating the genitourinary system.

Polygenic genetic variation affecting antibody formation underlies hypertensive renal injury in the stroke-prone spontaneously hypertensive rat

During development of the spontaneously hypertensive rat (SHR), several distinct but closely related lines were generated. Most lines are resistant to hypertensive renal disease. However, the SHR-A3 line (stroke-prone SHR) experiences end-organ injury (EOI) and provides a model of injury susceptibility that can be used to uncover genetic causation. In the present study, we generated a congenic line in which three distinct disease loci in SHR-A3 are concurrently replaced with homologous loci from an injury-resistant SHR line (SHR-B2). Verification that all three loci were homozygously replaced in this triple congenic line [SHR-A3(Trip B2)] while the genetic background of SHR-A3 was fully retained was obtained by whole genome sequencing. Congenic genome substitution was without effect on systolic blood pressure [198.9 ± 3.34 mmHg, mean ± SE, SHR-A3(Trip B2) = 194.7 ± 2.55 mmHg]. Measures of renal injury (albuminuria, histological injury scores, and urinary biomarker levels) were reduced in SHR-A3(Trip B2) animals, even though only 4.5 Mbases of the 2.8 Gbases of the SHR-B2 genome (0.16% of the genome) was transferred into the congenic line. The gene content of the three congenic loci and the functional effects of gene polymorphism within suggest a role of immunoglobulin in EOI pathogenesis. To prove the role of antibodies in EOI in SHR-A3, we generated an SHR-A3 line in which expression from the immunoglobulin heavy chain gene was knocked out (SHR-A3-IGHKO). Animals in the SHR-A3-IGHKO line lack B cells and immunoglobulin, but the hypertensive phenotype is not affected. Renal injury, however, was reduced in this line, confirming a pathogenic role for immunoglobulin in hypertensive EOI in this model of heritable risk.NEW & NOTEWORTHY Here, we used a polygenic animal model of hypertensive renal disease to show that genetic variation affecting antibody formation underlies hypertensive renal disease. We proved the genetic thesis by generating an immunoglobulin knockout in the susceptible animal model.

IgG4 Autoimmune Disease Masquerading As Oroantral Fistula

IgG4-related disease (IgG4-RD) is an immune-mediated disorder that involves multiple organs and is characterized by the infiltration of lymphoplasmacytic cells, including IgG4-positive plasma cells, along with storiform fibrosis and obliterative phlebitis in the inflamed organs. The primary sites affected by this condition include the pancreas, bile ducts, salivary glands, aorta, lungs, kidneys, meninges, lacrimal glands, mediastinal lymph nodes, and retroperitoneum. The pathogenesis is linked to a type 2 T-helper-cell cytokine profile and the involvement of regulatory T cells. However, the exact mechanism is still unknown. Patients with IgG4-related disease are frequently misdiagnosed as having malignancies due to the resemblance of the lesions to infections or other immune-mediated diseases and certain tumors, such as pancreatic cancer and pseudo-renal pelvis tumor. Prompt identification of IgG4-related disease is essential as a delayed diagnosis until advanced stages can result in severe organ damage and potentially fatal outcomes, despite the disease being highly responsive to treatment. This report presents a highly unusual case of IgG4-related disease (IgG4-RD) with an atypical presentation in a 38-year-old female patient. The patient sought medical attention in the emergency department due to nasal septal erosions and an oral-antral fistula. Nasal cultures were conducted and indicated the presence of Klebsiella ozaena. Subsequent investigations, including a nasal biopsy, confirmed the diagnosis of IgG4-related autoimmune disease.

Update on classification, diagnosis, and management of immunoglobulin G4-related disease

Immunoglobulin G4-related disease (IgG4-RD) is a newly recognized chronic fibro-inflammatory autoimmune disease, and its recognition has been constantly increasing worldwide over the last few years. A correct and timely recognition, as well as appropriate intervention, is crucial for the treatment of IgG4-RD. For certain subtypes of IgG4-RD, organ-specific criteria are formulated to make the diagnosis more accurate. New biomarkers have emerged in the recent years to aid the disease diagnosis, its prognosis prediction, as well as therapy response monitoring. Although recurrence is very common in IgG4-RD, glucocorticoid is still the first-line treatment for the majority of patients. The factors that affect the likelihood of disease relapse are multifaceted. The selection strategy of various steroid-sparing agents is still being explored. Besides, when patients have special sites involvement leading to severe clinical conditions, surgical operation or interventional therapy should also be considered. An update on classification, diagnosis, and management of IgG4-RD is provided in the current study to fully elucidate the recommended clinical practice of this mysterious disease.

Diagnostic Dilemma: Cardiorenal Syndrome As an Unusual Presentation of IgG4-Related Disease

IgG4-related kidney disease (IgG4 RKD) is a rare clinical entity characterized by lymphoplasmacytic infiltration rich in IgG4-positive plasma cells along with fibrosis affecting several organs. Tubulointerstitial nephritis is commonly the predominant finding on kidney biopsy. Our patient was admitted with a provisional diagnosis of cardiorenal syndrome of unknown etiology. The patient was dialysis dependent for around 45 days following which kidney biopsy revealed features of acute tubulointerstitial nephritis (ATIN) with IgG4-positive plasma cells and no glomerular involvement. Positron emission tomography-computed tomography was supportive of findings of sialadenitis along with myocarditis. Our patient responded to treatment with steroids with definitive improvement in both renal and cardiac functions. This case highlights the importance of IgG4 RKD as an important differential in patients with ATIN presenting as a clinical syndrome.

Multi-Organ Involvement of Immunoglobulin G4-Related Disease

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory condition of unknown etiology, with presumed autoimmune mechanisms. It is characterized by high levels of IgG4 and variable clinical manifestations. It can involve one or multiple organs. Herein, we reported the case of a 62-year-old man with three organs involvement. He initially presented with recurrent jaundice. Laboratory analysis revealed cholestasis, high gamma-globulin levels, renal failure, and proteinuria. Abdominal Magnetic Resonance Imaging (MRI) showed segmental strictures of the left intrahepatic bile ducts and the wirsung duct with an increased volume of the pancreas and diffuse bilateral enlargement of the kidneys. Laboratory tests revealed high IgG4 levels (770 mg/dL). Based on the biological and radiological findings, we have suggested the diagnosis of systemic IgG4-related disease involving bile ducts, the pancreas, and probably the kidneys. Renal biopsy revealed lymphoplasmacytic infiltrate and fibrosis, but no IgG4-positive cell. The patient received corticosteroid therapy with a complete resolution of all symptoms and a rapid normalization of all blood tests. The present case underlines the complexity of IgG4-RD because of its variable clinical presentation. The diagnosis is challenging and should be carefully assessed for possible multi-organ involvement.

Disparities between IgG4-related kidney disease and extrarenal IgG4-related disease in a case-control study based on 450 patients

We aimed to compare the demographic, clinical and laboratory characteristics between IgG4-related kidney disease (IgG4-RKD+) and extrarenal IgG4-related disease (IgG4-RKD−) in a large Chinese cohort, as well as describing the radiological and pathological features of IgG4-RKD+. We retrospectively analyzed the medical records of 470 IgG4-related disease (IgG4-RD) patients at Peking University People’s Hospital from January 2004 to January 2020. The demographic, clinical, laboratory, radiological and pathological characteristics between IgG4-RKD+ and IgG4-RKD− were compared. Twenty IgG4-RD patients who had definite etiology of renal impairment including diabetes, hypertension and etc. were excluded. Among the remained 450 IgG4-RD patients, 53 were diagnosed with IgG4-RKD+ . IgG4-RKD+ patients had older age at onset and at diagnosis. Male to female ratio of IgG4-RKD+ patients is significantly higher. In the IgG4-RKD+ group, the most commonly involved organs were salivary gland, lymph nodes and pancreas. It was found that renal function was impaired in approximately 40% of IgG4-RKD+ patients. The most common imaging finding is multiple, often bilateral, hypodense lesions. Male sex, more than three organs involved, and low serum C3 level were risk factors for IgG4-RKD+ in IgG4-RD patients. These findings indicate potential differences in pathogenesis of these two phenotypes.

An enigmatic case of IgG4-related nephropathy and an updated review of the literature

IgG4-related disease (IgG4-RD) is still an underestimated disorder which affects multiple organs, and its recognition as a distinct clinical disease has been only proved in the recent decades. The renal involvement has been documented in approximately 15% of patients with IgG4-RD, and the typical manifestation is a tubulo-interstitial nephritis. The main histological findings in IgG4-RD are typically a dense tissue infiltration of IgG4-positive plasma cells, storiform fibrosis, obliterative phlebitis, and frequently elevated IgG4 serum levels. Herein we report our atypical and peculiar clinical presentation of an IgG4-related nephropathy (IgG4-RN) and the remarkable response to rituximab (RTX) treatment at the renal imaging with computerized tomography assessment. The current nephrological evidences support the renal function recovery after steroids or steroids plus RTX therapy, even if the renal imaging data are not always shown. In a complex and enigmatic clinical scenario such as the IgG4-RN, both the renal biopsy and the renal imaging before and after the immunosuppressive therapy become mandatory tools to thoroughly define the diagnosis, the management and the response to the immunological therapy.

Secondary Membranous Nephropathy. A Narrative Review

Membranous nephropathy (MN) is a common cause of proteinuria and nephrotic syndrome all over the world. It can be subdivided into primary and secondary forms. Primary form is an autoimmune disease clinically characterized by nephrotic syndrome and slow progression. It accounts for ~70% cases of MN. In the remaining cases MN may be secondary to well-defined causes, including infections, drugs, cancer, or autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), urticarial vasculitis, sarcoidosis, thyroiditis, Sjogren syndrome, systemic sclerosis, or ankylosing spondylitis. The clinical presentation is similar in primary and secondary MN. However, the outcome may be different, being often related to that of the original disease in secondary MN. Also, the treatment may be different, being targeted to the etiologic cause in secondary MN. Thus, the differential diagnosis between primary and secondary MN is critical and should be based not only on history and clinical features of the patient but also on immunofluorescence and electron microscopy analysis of renal biopsy as well as on the research of circulating antibodies. The identification of the pathologic events underlying a secondary MN is of paramount importance, since the eradication of the etiologic factors may be followed by remission or definitive cure of MN. In this review we report the main diseases and drugs responsible of secondary MN, the outcome and the pathogenesis of renal disease in different settings and the possible treatments.

Immunoglobulin G4-related Disease of the Genitourinary System: Spectrum of Imaging Findings and Clinical-Pathologic Features

Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory disease characterized by focal or diffuse organ infiltration of IgG4-bearing plasma cells. The diagnosis of IgG4-RD is based on a combination of clinical, serologic, radiologic, and histopathologic findings. IgG4-RD has been reported to affect almost all organ systems. The kidney is the most frequently involved of the genitourinary organs. The most common renal manifestation of IgG4-RD is IgG4-RD tubulointerstitial nephritis, followed by membranous glomerulonephropathy and, less frequently, obstructive nephropathy involving the renal pelvis, ureter, or retroperitoneum. Renal parenchymal lesions may appear as multiple nodular lesions, diffuse patchy infiltrative lesions, or a single nodular lesion. Multiple small nodular cortical lesions are the most common imaging findings of IgG4-RD involving the kidney. Renal pelvic, sinus, or perinephric lesions can also occur. IgG4-RD involvement of other genitourinary organs including the ureter, bladder, urethra, and male and female reproductive organs is rare compared with kidney involvement but may show variable imaging findings such as a localized mass within or surrounding the involved organ or diffuse enlargement of the involved organ. Imaging findings of IgG4-RD involving the genitourinary system are nonspecific but should be differentiated from inflammatory and neoplastic lesions that mimic IgG4-RD. The online slide presentation from the RSNA Annual Meeting is available for this article. ^©RSNA, 2020.

A Case of an IgG4-Related Disease Mimicking Malignancy and Resolving With Steroids

A 77-year-old African American female was referred to oncology for evaluation of an adrenal fossa mass detected on computed tomography scan of the abdomen and pelvis (CT-scan A/P) that was ordered as a work-up for painless hematuria. Further evaluation by positron emission tomography (PET) scan showed hypermetabolic masses in the left suprarenal and right iliac region. The biopsy of the right iliac mass was consistent with IgG4-related disease (IgG4RD). It was supported by an elevated serum IgG4 level. She was treated with prednisone with a good response.

Case report: IgG4-related renal disease co-existing with retroperitoneal fibrosis

A 51-year-old woman visited our clinic for orthopnea, chest discomfort, and facial and leg edema. Acute kidney injury and pleural effusion were diagnosed and she received hemodialysis. This is a rare case of IgG4-related disease diagnosed by renal biopsy in the patient with retroperitoneal fibrosis and severe acute kidney injury, which progressed rapidly and required hemodialysis without markedly elevated serum IgG4 level and urinary tract obstruction. Immunostaining of a kidney biopsy revealed IgG4-related renal disease and magnetic resonance imaging showed retroperitoneal fibrosis in the paraspinal and presacral areas. After 3 days of glucocorticoid treatment, renal function and bilateral pleural effusion were restored. Another 2 months of glucocorticoid treatment decreased the extent of retroperitoneal fibrosis on follow-up abdominal computed tomography. IgG4-related disease is a recently recognized fibro-inflammatory condition with a dense lymphoplasmacytic infiltration of IgG4-positive plasma cells. The kidney and retroperitoneum are the frequently associated organs in IgG4-related disease. This case shows that IgG4-related disease can involve the kidney and/or other organs and be diagnosed by kidney biopsy.

IgG4-Related Disease Manifesting as Hypocomplementemic Tubulointerstitial Nephritis: A Rare Case Report and Literature Review

Immunoglobulin G4-related disease (IgG4-RD) is a chronic fibrosing inflammatory systemic disorder that has been recognized relatively recently in the medical literature. Little is known about the exact disease pathogenesis and epidemiology. IgG4-RD may be asymptomatic or may have minimal symptoms or involve multiple organs with overt symptoms. The different phenotypes of IgG4-RD can lead to delayed or incorrect diagnosis. We report the case of a 66-year-old male with coal worker's pneumoconiosis who presented with progressive kidney disease and was diagnosed with tubulointerstitial nephritis due to IgG4-RD. The patient was noted to have progressive kidney disease, skin involvement, worsening interstitial lung disease, complete vision loss in the left eye, and retroperitoneal fibrosis. Serologic workup revealed elevated inflammatory markers, IgG4 and IgG1 levels, and hypocomplementemia. A tissue biopsy helped us establish a definitive diagnosis of IgG4-RD and initiate treatment with glucocorticoids to prevent further progression of kidney disease and other end-organ damage.

Steroid Therapy and Steroid Response in Autoimmune Pancreatitis

Autoimmune pancreatitis (AIP), a unique subtype of pancreatitis, is often accompanied by systemic inflammatory disorders. AIP is classified into two distinct subtypes on the basis of the histological subtype: immunoglobulin G4 (IgG4)-related lymphoplasmacytic sclerosing pancreatitis (type 1) and idiopathic duct-centric pancreatitis (type 2). Type 1 AIP is often accompanied by systemic lesions, biliary strictures, hepatic inflammatory pseudotumors, interstitial pneumonia and nephritis, dacryoadenitis, and sialadenitis. Type 2 AIP is associated with inflammatory bowel diseases in approximately 30% of cases. Standard therapy for AIP is oral corticosteroid administration. Steroid treatment is generally indicated for symptomatic cases and is exceptionally applied for cases with diagnostic difficulty (diagnostic steroid trial) after a negative workup for malignancy. More than 90% of patients respond to steroid treatment within 1 month, and most within 2 weeks. The steroid response can be confirmed on clinical images (computed tomography, ultrasonography, endoscopic ultrasonography, magnetic resonance imaging, and 18F-fluorodeoxyglucose-positron emission tomography). Hence, the steroid response is included as an optional diagnostic item of AIP. Steroid treatment results in normalization of serological markers, including IgG4. Short- and long-term corticosteroid treatment may induce adverse events, including chronic glycometabolism, obesity, an immunocompromised status against infection, cataracts, glaucoma, osteoporosis, and myopathy. AIP is common in old age and is often associated with diabetes mellitus (33-78%). Thus, there is an argument for corticosteroid therapy in diabetes patients with no symptoms. With low-dose steroid treatment or treatment withdrawal, there is a high incidence of AIP recurrence (24-52%). Therefore, there is a need for long-term steroid maintenance therapy and/or steroid-sparing agents (immunomodulators and rituximab). Corticosteroids play a critical role in the diagnosis and treatment of AIP.

Successful treatment of tubulointerstitial nephritis in immunoglobulin G4-related disease with rituximab: A case report

BACKGROUND

Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated condition that consisted of disorders that share particular clinical, serologic and pathologic properties. The common presentation of disease includes tumor-like swelling of involved organs and the histopathological findings are a lymphoplasmacytic infiltrate enriched with IgG4-positive plasma cells, and a variable degree of fibrosis that has a characteristic "storiform" pattern in biopsy specimens of tumor-like masses. Major presentations of this disease, which often affects more than one organ, include autoimmune pancreatitis, salivary gland disease (sialadenitis), orbital disease and retroperitoneal fibrosis. The steroid treatment is essential for the treatment of the disease however, other immunosuppressive drugs including cyclophosphamide or rituximab could be an option in resistant cases.

CASE SUMMARY

Herein, we reported a 34-year-old woman whom previously had diagnosed with asthma, rheumatoid arthritis and Sjögren’s syndrome (SS) referred our nephrology department due to acute kidney failure development at the last rheumatology visit. After kidney biopsy she has been diagnosed with IgG4-RD and tubuluointerstitial nephritis. She had been accepted resistant to steroid, mycophenolate mofetil, methotrexate and azathioprine therapies due to receiving in last two years. She refused to receive cyclophosphamide due to potential gonadotoxicity of the drug. Thus, rituximab therapy was considered. She received 1000 mg infusion, 15 d apart and 6 mo later it has been administered same protocol. After one year from the last rituximab dose serum creatinine decreased from 4.4 mg/dL to 1.6 mg/dL, erythrocyte sedimentation rate decreased from 109 mm/h to 13 mm/h [reference range (RR) 0-20], and C-reactive protein decreased from 55.6 mg/L to 5 mg/L (RR 0–6). All pathologic lymph nodes and masses were also disappeared.

CONCLUSION

Patients with IgG4-RD usually misdiagnosed with rheumatologic diseases including systemic lupus erythematous or SS and also they were screened for the presence of malignancy. Rituximab could be an important treatment option in cases with steroid resistant tubulointerstitial nephritis in IgG4-RD.

IgG4-related sialadenitis complicated with type III mixed cryoglobulinemia: A case report

RATIONALE

IgG4-related disease (IgG4-RD) is a systemic autoimmune disease and mixed cryoglobulinemia may be caused by autoimmune diseases. However, so far only 1 case of IgG4-RD complicated with mixed cryoglobulinemia is reported. Our case further confirms the close relationship between these 2 diseases.

PATIENT CONCERNS

A 55-year-old female was admitted because of dry mouth and teeth falling off.

DIAGNOSES

The patient was diagnosed as IgG4-related sialadenitis (IgG4-RS) complicated with type III mixed cryoglobulinemia. IgG4-RS was confirmed by elevated serum IgG4 levels and diffuse IgG4 plasmocyte infiltration and storiform fibrosis in the interstitium of labial gland. Type III mixed cryoglobulinemia was confirmed by positive serum cryoglobulins and no monoclonal immunoglobulin in serum and urine.

INTERVENTIONS AND OUTCOMES

After treatment with prednisone and cyclophosphamide, serum cryoglobulins rapidly turned negative with the remission of IgG4-RS.

LESSONS

Type III mixed cryoglobulinemia can be caused by IgG4-RS, and the underlying mechanisms need to be further explored.

IgG4-Related Kidney Disease: A Curious Case of Interstitial Nephritis with Hypocomplementemia

IgG4-related kidney disease has been relatively newly recognized over the last two decades as a combination of an autoimmune and allergic disorder, with elevated serum IgG4 level and hypocomplementemia among its characteristic features. Here we report the case of a man with interstitial nephritis presenting with acute kidney injury and hypocomplementemia but normal serum IgG4 level and provide a literature review of IgG4-related kidney disease. This case highlights the importance of IgG4-related kidney disease as an important differential diagnosis in any patient presenting with a clinical syndrome mimicking acute interstitial nephritis with hypocomplementemia. A high index of suspicion with a low threshold for performing a native kidney biopsy would be paramount as patients do respond well to corticosteroid therapy.

Eosinophilia and Kidney Disease: More than Just an Incidental Finding?

Peripheral blood eosinophilia (PBE), defined as 500 eosinophils or above per microliter (µL) blood, is a condition that is not uncommon but often neglected in the management of patients with chronic kidney disease (CKD), acute kidney injury (AKI), or patients on renal replacement therapy (RRT). The nature of PBE in the context of kidney diseases is predominantly secondary or reactive and has to be distinguished from primary eosinophilic disorders. Nonetheless, the finding of persistent PBE can be a useful clue for the differential diagnosis of underdiagnosed entities and overlapping syndromes, such as eosinophilic granulomatosis with polyangiitis (EGPA), IgG4-related disease (IgG4-RD), acute interstitial nephritis (AIN), or the hypereosinophilic syndrome (HES). For patients on RRT, PBE may be an indicator for bio-incompatibility of the dialysis material, acute allograft rejection, or Strongyloides hyperinfection. In a subset of patients with EGPA, eosinophils might even be the driving force in disease pathogenesis. This improved understanding is already being used to facilitate novel therapeutic options. Mepolizumab has been licensed for the management of EGPA and is applied with the aim to abrogate the underlying immunologic process by blocking interleukin-5. The current article provides an overview of different renal pathologies that are associated with PBE. Further scientific effort is required to understand the exact role and function of eosinophils in these disorders which may pave the way to improved interdisciplinary management of such patients.

Severe Acute Kidney Injury and Multiple Organ Failure in a 17-Day-Old Newborn: When Pathology Makes the Difference

Rationale:

Acute tubulointerstitial nephritis (ATIN) in children is most commonly due to allergic drug reactions. In neonates, diagnosis of ATIN is clinically suspected and a kidney biopsy is not routinely performed.

Presenting concern:

A 17-day-old newborn presented with vomiting and dehydration, along with anuric acute kidney injury, severe electrolyte disturbances, hypocomplementemia, and thrombocytopenia. Abdominal ultrasound revealed bilateral nephromegaly and hepatosplenomegaly. The patient was promptly started on intravenous (IV) fluid and broad-spectrum antibiotics. His electrolyte disturbances were corrected as per standard guidelines. The rapid progressive clinical deterioration despite maximal treatment and the unclear etiology influenced the decision to proceed to a kidney biopsy. Histopathological findings revealed diffuse interstitial edema with a massive polymorphic cellular infiltrate and destruction of tubular structures, consistent with severe ATIN. Elements of thrombotic microangiopathy (TMA) were observed.

Diagnosis:

The clinical presentation combined with imaging and histopathological findings was suggestive of ATIN caused by a severe acute bacterial pyelonephritis.

Intervention:

Methylprednisolone pulses followed by oral prednisolone were administered. Antibiotics were continued for 10 days. The patient was kept on invasive mechanical ventilation and on peritoneal dialysis for 12 days.

Outcome:

His condition stabilized following steroid pulses. His renal function progressively improved, and renal replacement therapy was weaned off. His renal ultrasound normalized. He has maintained a normal blood pressure, urinalysis, and renal function over the past 5 years.

Novel finding:

This case reports a severe presentation of acute bacterial pyelonephritis in a neonate. It highlighted the involvement of complement activation in severe infectious process. Histopathological findings of ATIN and TMA played a crucial role in understanding the physiopathology and severity of the disease.