IgG4-related tubulointerstitial nephritis accompanied with cystic formation

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.

Recognizing IgG4-related tubulointerstitial nephritis

PURPOSE OF THE REVIEW

Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder affecting nearly all organs, including the kidney. Tubulointerstitial nephritis (IgG4-TIN) is the most common form of IgG4-related kidney disease (IgG4-RKD) and is the focus of this concise review.

OBJECTIVE

The study aims to describe when IgG4-TIN should be suspected and to summarize the diagnosis, treatment, and natural history of the disease.

SOURCES OF INFORMATION

Ovid MEDLINE, Google Scholar, and PubMed were searched for full-text English language articles up to January 2016. References included in the manuscript were chosen at the authors' discretion based on their relevance to the subject of the review.

FINDINGS

IgG4-TIN should be considered in patients presenting with abnormal urinalysis, abnormal kidney function, renal lesions on imaging, and elevated IgG, IgE, or hypocomplementemia. Diagnosis of IgG4-TIN requires a combination of histologic features (plasma cell-enriched TIN with >10 IgG4+ plasma cells/hpf, +/- TBM immune complex deposits in many cases) and at least one of the following:Characteristic radiologic findings (small peripheral low-attenuation cortical nodules, round or wedge-shaped lesions, or diffuse patchy involvement)Elevated serum IgG4 levelCharacteristic findings of IgG4-RD in other organs Other conditions such as lupus, vasculitis, diabetic nephropathy, and lymphoma must be excluded, as these can also present with IgG4+ plasma cells in the renal parenchyma. IgG4-TIN is generally responsive to steroids and B cell depletion with rituximab, but relapses are common and patients require close long-term follow-up.

LIMITATIONS

Available data on IgG4-TIN are from retrospective observational studies.

IMPLICATIONS

IgG4-TIN is a distinct and emerging subtype of interstitial nephritis. Nephrologists must be aware of this entity and how to definitively diagnose and treat it. Prospective studies and ideally multi-center clinical trials are needed to study the epidemiology, treatment, and natural history of this disease.

IgG4-related nephropathy

IgG4-related disease (IgG4-RD) is a recently recognized disorder, often with multiple organ involvement, characterized by dense tissue infiltration of IgG4-positive plasma cells, storiform fibrosis, obliterative phlebitis and frequently elevated serum IgG4 concentration. The kidney can be involved either directly or indirectly. The most frequent direct renal manifestations of IgG4-RD are IgG4-related tubulointerstitial nephritis (TIN) and membranous glomerulonephropathy. Retroperitoneal fibrosis (RPF) is another condition that is frequently IgG4-related and that can indirectly affect the kidney causing ureteral obstruction and hydronephrosis. Contrast-enhanced computerized tomography, magnetic resonance imaging and (18)F-fluorodeoxyglucose positron emission tomography/computed tomography show different imaging findings and are useful tools for monitoring therapeutic response. Steroid treatment is the first line of therapy, but relapsing or refractory forms of the disease are frequently observed and require more aggressive therapeutic approaches. At our centre, we treated three cases of aggressive IgG4-related TIN and two cases of IgG4-related RPF with an intensified, immune suppressive protocol, obtaining good results without severe adverse effects.

IgG4-related renal disease: clinical and pathological characteristics

IgG4-related disease is a recently established systemic condition. Tubulointerstitial nephritis is the most common renal manifestation. Glomerular lesions, particularly membranous glomerulonephritis, can develop simultaneously. Some patients present with serological renal dysfunction associated with elevated IgG or IgE levels and hypocomplementemia, while others are incidentally found to have abnormalities in kidneys on imaging. A majority of patients with IgG4-related kidney disease have similar lesions at other anatomical sites, which help us to suspect this condition. Serum IgG4 elevation (>135 mg/dL) is the most, although not entirely, specific marker for the diagnosis. Imaging findings varies from small nodules to bilateral diffuse abnormalities. In addition to the renal parenchyma, the renal pelvis and perirenal adipose tissue can be affected. Histological features include dense lymphoplasmacytic infiltration, storiform or "bird's eye" fibrosis (highlighted by PAM stain), and IgG4-positive plasma cell infiltration (>10 cells/high-power field and IgG4/IgG-positive cell ratio >40%). Immune complex deposition is detectable in the tubular basement membrane by immunofluorescence and/or electron microscopy. Patients usually respond well to corticosteroids, but highly active diseases may require other immunosuppressive therapies. Further investigations will be required to fully understand pathophysiology underlying this emerging condition.