Glomerulonephritis, the inflammatory disease of the glomerulus produced by immune-mediated injury to the filtration unit of the kidney, encompasses a diverse spectrum of conditions unified by the common pathological theme of inflammatory damage to the glomerular capillary tuft, the podocytes, and the surrounding mesangium, but distinguished by widely varying immunological mechanisms, histological patterns, clinical presentations, natural histories, and treatment approaches that make glomerulonephritis one of the most intellectually complex and clinically challenging areas of nephrology. From the acute post-infectious glomerulonephritis that typically resolves spontaneously in children following streptococcal infection to the rapidly progressive crescentic glomerulonephritis that can destroy kidney function within weeks in the absence of immediate aggressive immunosuppressive treatment, from the relapsing and remitting course of IgA nephropathy to the progressive proteinuria and nephrotic syndrome of membranous nephropathy, the clinical diversity of glomerulonephritis reflects the extraordinary range of immunological mechanisms that can target the glomerulus and produce its pathological consequences.
The clinical importance of glomerulonephritis as a cause of kidney disease extends beyond its individual clinical presentations to its collective contribution to the global burden of chronic kidney disease and end-stage renal disease. Glomerulonephritis is responsible for approximately ten to fifteen percent of all end-stage renal disease in developed countries and a higher proportion in some developing regions where post-infectious glomerulonephritis and other infection-associated nephropathies are more prevalent, establishing it as the third most common cause of end-stage renal disease after diabetes and hypertension. The diseases within the glomerulonephritis spectrum show characteristic age and demographic distributions, with IgA nephropathy being the most common primary glomerulonephritis worldwide and predominantly affecting young adult males, membranous nephropathy being the most common cause of nephrotic syndrome in older adults in developed countries, and lupus nephritis disproportionately affecting young women of childbearing age with the most significant racial disparity in prevalence and severity observed in women of African and Hispanic ancestry.
The diagnosis of glomerulonephritis requires the integration of clinical presentation, urinalysis findings, serological biomarkers, and kidney biopsy histopathology, with the kidney biopsy remaining the gold standard for establishing the specific diagnosis and histological class that determine prognosis and guide immunosuppressive treatment decisions. The clinical syndromes of glomerulonephritis are broadly classified as nephritic syndrome, characterized by hematuria with dysmorphic red blood cells and red blood cell casts, variable proteinuria, hypertension, and declining glomerular filtration rate reflecting inflammatory disruption of the filtration barrier, and nephrotic syndrome, characterized by heavy proteinuria above 3.5 grams per day producing hypoalbuminemia, edema, hyperlipidemia, and lipiduria reflecting massive loss of albumin and other plasma proteins through a severely damaged filtration barrier. Many glomerulonephritis conditions produce features of both syndromes simultaneously or at different stages of their clinical course, reflecting the mixed patterns of glomerular injury that characterize the most complex inflammatory nephritides.
IgA Nephropathy: The Most Common Glomerulonephritis
IgA nephropathy, first described by Jean Berger in 1968 through the observation of IgA deposits in the mesangium of renal biopsies, is the most prevalent primary glomerulonephritis worldwide, affecting approximately three persons per hundred thousand annually in regions with systematic biopsy practices and accounting for more than forty percent of all primary glomerulonephritis diagnoses in Asia and approximately twenty to thirty percent in Western countries. The pathophysiology of IgA nephropathy involves a multi-hit process beginning with the overproduction of aberrantly glycosylated IgA1, in which galactose is deficient from the O-glycan chains of the hinge region of the IgA1 heavy chain, followed by the production of IgG or IgA autoantibodies against this galactose-deficient IgA1, the formation of immune complexes that deposit in the glomerular mesangium, and the subsequent mesangial cell activation with complement activation, cytokine production, and the recruitment of inflammatory cells that produce the glomerular injury observed on biopsy.
The clinical presentation of IgA nephropathy spans a wide spectrum from the asymptomatic microscopic hematuria and mild proteinuria discovered incidentally on urinalysis in young adults to the episodic macroscopic hematuria that characteristically follows upper respiratory tract infections by one to two days in the synpharyngitic hematuria presentation, to the progressive renal insufficiency with heavy proteinuria that characterizes the most aggressive clinical course. The temporal relationship between mucosal infection and macroscopic hematuria, with the IgA nephropathy hematuria occurring simultaneously with or immediately after the infection rather than the ten to fourteen day interval of post-streptococcal nephritis, reflects the IgA system’s direct connection to mucosal immunity and the mucosal infection as a trigger for the abnormal IgA1 production that drives the disease. The long-term prognosis of IgA nephropathy is substantially more serious than its frequent asymptomatic or mildly symptomatic presentation might suggest, with approximately thirty to forty percent of affected individuals progressing to end-stage renal disease within twenty to thirty years of diagnosis and with clinical risk factors including heavy proteinuria, hypertension, impaired glomerular filtration rate at presentation, and histological risk features including crescents and extensive segmental sclerosis predicting the highest progression risk.
The therapeutic landscape for IgA nephropathy has been substantially transformed by the approval of the targeted release formulation of budesonide, which releases the corticosteroid at the Peyer’s patches of the ileum where the aberrant IgA1-producing B cells responsible for the disease are concentrated, reducing mucosal IgA1 overproduction with substantially lower systemic corticosteroid exposure than conventional oral prednisolone. The NEFIGAN and PROTECT randomized controlled trials demonstrated significant proteinuria reduction and in the PROTECT trial preservation of glomerular filtration rate with targeted release budesonide compared to placebo in patients with IgA nephropathy at risk of progression, establishing this as the first disease-specific treatment for IgA nephropathy to gain regulatory approval based on robust randomized clinical trial evidence. Sparsentan, the dual endothelin and angiotensin receptor antagonist, demonstrated superior proteinuria reduction compared to irbesartan in the PROTECT trial with potential glomerular filtration rate preservation benefits emerging in longer follow-up data, providing an additional therapeutic option addressing the hemodynamic and endothelin-mediated inflammatory pathways that amplify IgA nephropathy progression alongside the immunological drivers of the disease.
Membranous Nephropathy and Nephrotic Syndrome
Membranous nephropathy is the most common cause of nephrotic syndrome in adults over fifty years of age in developed countries and a major contributor to progressive kidney disease in older patients, caused in approximately eighty percent of primary cases by autoantibodies against the M-type phospholipase A2 receptor expressed on the surface of glomerular podocytes. The binding of anti-PLA2R IgG4 antibodies to podocyte PLA2R activates complement through the lectin pathway, generating the membrane attack complex that inserts into the glomerular basement membrane and damages the podocyte plasma membrane, producing the characteristic subepithelial immune deposits visible on electron microscopy and the spike formation on the outer glomerular basement membrane surface visible on Jones silver stain light microscopy that are the diagnostic hallmarks of membranous nephropathy. The pathophysiological consequence of this podocyte membrane attack is the disruption of the filtration barrier selectivity that produces the massive proteinuria of nephrotic syndrome, with urinary protein losses typically ranging from three to fifteen grams per day in symptomatic patients.
The clinical manifestations of nephrotic syndrome in membranous nephropathy reflect the physiological consequences of sustained massive proteinuria and the hypoalbuminemia it produces. Peripheral edema, initially subtle and most prominent in dependent areas including the ankles and lower legs, can progress in severe hypoalbuminemia to massive ascites, pleural effusions, and periorbital edema that produce the anasarca characteristic of severe nephrotic syndrome. Hyperlipidemia, driven by the hepatic upregulation of lipoprotein synthesis in response to low oncotic pressure from hypoalbuminemia and by the reduced peripheral lipid clearance from urinary loss of lipoprotein lipase and its cofactors, produces marked elevations of total cholesterol, low-density lipoprotein, and triglycerides that significantly amplify the cardiovascular risk of nephrotic syndrome and may require specific lipid-lowering therapy alongside treatment of the underlying nephropathy. Hypercoagulability in nephrotic syndrome, from the urinary loss of anticoagulant proteins including antithrombin III, protein S, and protein C alongside relative preservation of pro-coagulant factors and the elevated fibrinogen from hepatic acute-phase response, produces the substantially elevated risk of venous and arterial thromboembolic events that is one of the most serious complications of heavy proteinuria in membranous nephropathy.
The management of primary membranous nephropathy has been revolutionized by the development of the anti-CD20 monoclonal antibody rituximab as a targeted B cell-depleting therapy that eliminates the anti-PLA2R antibody-producing B cell clones responsible for the pathological autoimmune response, producing sustained reductions in anti-PLA2R antibody titers and immunological and clinical remission in a substantial proportion of treated patients. The MENTOR trial, a landmark randomized controlled trial comparing rituximab to cyclosporine for the treatment of membranous nephropathy, demonstrated that rituximab produced superior proteinuria remission at twenty-four months with more durable responses and fewer adverse effects than cyclosporine, establishing rituximab as the preferred first-line immunosuppressive treatment for high-risk primary membranous nephropathy in most contemporary treatment guidelines. The ability to monitor anti-PLA2R antibody titers as a biomarker of disease activity allows individualization of rituximab dosing and timing of re-treatment, with declining antibody titers predicting subsequent clinical remission and rising titers providing early warning of disease reactivation that may allow pre-emptive intervention before nephrotic syndrome recurs.
Rapidly Progressive Glomerulonephritis and Emergency Management
Rapidly progressive glomerulonephritis, the most severe acute presentation of glomerulonephritis characterized by a rapid decline in glomerular filtration rate of fifty percent or more within weeks to months and the pathological finding of glomerular crescents in more than fifty percent of glomeruli on kidney biopsy, represents a true nephrological emergency in which delays in diagnosis and treatment directly translate into irreversible nephron loss and progression to dialysis dependence. The three principal immunological mechanisms producing rapidly progressive glomerulonephritis are anti-glomerular basement membrane antibody disease, in which linear IgG deposits along the glomerular basement membrane from autoantibodies against the alpha-3 chain of type IV collagen produce severe crescentic nephritis often accompanied by pulmonary hemorrhage in Goodpasture syndrome; immune complex-mediated crescentic glomerulonephritis from conditions including lupus nephritis, IgA nephropathy, post-infectious glomerulonephritis, and cryoglobulinemic vasculitis; and pauci-immune crescentic glomerulonephritis from anti-neutrophil cytoplasmic antibody associated vasculitides including granulomatosis with polyangiitis and microscopic polyangiitis.
The clinical recognition of rapidly progressive glomerulonephritis requires awareness of the presentation of rapidly rising creatinine with urinalysis showing nephritic sediment of dysmorphic red blood cells, red blood cell casts, and variable proteinuria, alongside the systemic features of the underlying vasculitis or autoimmune condition that may include respiratory symptoms, sinusitis, skin rashes, joint involvement, or constitutional symptoms. The serological evaluation including anti-neutrophil cytoplasmic antibody testing for both cytoplasmic and perinuclear patterns, anti-glomerular basement membrane antibody, complement levels, antinuclear antibodies, and anti-double stranded DNA antibodies allows rapid classification of the likely immunological mechanism before kidney biopsy results are available, guiding emergency treatment decisions in the most severe presentations where delays for biopsy confirmation may not be clinically acceptable.
The treatment of rapidly progressive glomerulonephritis from anti-neutrophil cytoplasmic antibody vasculitis has been transformed by the rituximab data from the RAVE and RITUXVAS trials demonstrating non-inferiority of rituximab to cyclophosphamide for remission induction in granulomatosis with polyangiitis and microscopic polyangiitis, establishing rituximab as an alternative to cyclophosphamide that avoids the gonadal toxicity, hemorrhagic cystitis, and infection risk of the traditional alkylating agent approach. Plasma exchange, previously used extensively as adjunctive therapy for rapidly progressive glomerulonephritis to rapidly remove pathogenic autoantibodies from the circulation, was assessed in the PEXIVAS randomized controlled trial for anti-neutrophil cytoplasmic antibody vasculitis with severe kidney disease and found not to provide a significant benefit for the primary composite endpoint of end-stage renal disease or death at twelve months, challenging its routine use in this indication and refocusing attention on the immunosuppressive and targeted biological therapies that address the underlying autoimmune driving mechanism. The management of anti-glomerular basement membrane disease remains dependent on intensive plasma exchange to remove the pathogenic antibodies combined with high-dose glucocorticoids and cyclophosphamide to suppress ongoing antibody production, with the urgency of treatment reflecting the rapid and irreversible glomerular destruction that occurs during the period of active anti-glomerular basement membrane antibody exposure.