Membranous Nephropathy Medical Services in China

Membranous Nephropathy (MN) is a chronic autoimmune kidney disorder characterized by the thickening of the glomerular basement membrane due to immune complex deposition—primarily IgG and complement component C3—along the subepithelial surface of podocytes. This leads to podocyte injury, disruption of the filtration barrier, and consequent heavy proteinuria, often presenting as nephrotic syndrome (edema, hypoalbuminemia, hyperlipidemia, and thrombotic risk). MN is classified as primary (idiopathic, ~75% of cases) when no underlying cause is identified, or secondary when associated with conditions such as systemic lupus erythematosus, hepatitis B or C infection, solid tumors (e.g., lung, gastric, or colorectal cancers), autoimmune thyroid disease, or exposure to certain medications (e.g., NSAIDs, penicillamine, or gold salts). Pathogenesis centers on autoantibodies targeting podocyte antigens—most commonly phospholipase A2 receptor (PLA2R) in adults (found in ~70–80% of primary MN), and less frequently thrombospondin type-1 domain-containing 7A (THSD7A) or neural epidermal growth factor-like 1 (NELL-1). These antibodies trigger complement activation (via the lectin or alternative pathways), resulting in subepithelial immune deposits, podocyte foot process effacement, and progressive protein leakage. Epidemiologically, MN is the most common cause of adult-onset nephrotic syndrome in non-diabetic populations, with an incidence of approximately 8–10 cases per million per year globally. It peaks between ages 40–60, shows a male predominance (M:F ≈ 2:1), and exhibits higher prevalence in North America and Europe compared to Asia—though incidence in China is rising, likely reflecting improved diagnostic awareness and PLA2R testing availability. Key risk factors include older age, male sex, PLA2R antibody titer level and persistence, elevated serum creatinine at diagnosis, and non-immunologic comorbidities such as hypertension and obesity. Importantly, up to one-third of untreated patients experience spontaneous remission within 5 years; however, another third progress to end-stage kidney disease over 10–15 years without intervention. Quality of life is significantly impaired: persistent edema and fatigue limit physical activity and work capacity; recurrent infections and hypercoagulability increase hospitalization risk; dietary restrictions (low-salt, low-protein) affect psychosocial well-being; and long-term immunosuppression carries risks of diabetes, osteoporosis, cataracts, and malignancy. Patients also face anxiety related to unpredictable disease course, fertility concerns, and financial burden from repeated lab monitoring (PLA2R titers, urine protein-to-creatinine ratio), renal biopsies, and prolonged therapy. Early diagnosis via serologic testing (anti-PLA2R/THSD7A) and confirmatory kidney biopsy remains critical for risk stratification and timely, individualized treatment.

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults, characterized by immune-mediated thickening of the glomerular basement membrane due to subepithelial immune complex deposition. It is classified as either primary (idiopathic, ~75% of cases) or secondary (25%), with distinct etiologic profiles. Primary MN is strongly associated with autoantibodies targeting podocyte antigens—most notably phospholipase A2 receptor (PLA2R), present in ~70–80% of untreated cases; thrombospondin type-1 domain-containing 7A (THSD7A) accounts for ~5–10% of PLA2R-negative cases. Other less common autoantigens include neural epidermal growth factor-like 1 (NELL-1), exostosin 1/2 (EXT1/2), and semaphorin 3B (SEMA3B), reflecting heterogeneous autoimmune pathogenesis. Secondary MN arises from identifiable triggers, including infections (e.g., hepatitis B and C virus, syphilis, malaria), malignancies (particularly lung, gastric, colorectal, and renal cell carcinomas, as well as lymphoproliferative disorders), autoimmune diseases (systemic lupus erythematosus [SLE], rheumatoid arthritis, Sjögren syndrome), and exposure to certain drugs (e.g., NSAIDs like ibuprofen and naproxen, penicillamine, gold salts, mercury, and rarely anti-TNF agents). Notably, malignancy-associated MN often precedes cancer diagnosis by months to years, underscoring the importance of age-appropriate oncologic screening in newly diagnosed patients over age 50.

Risk factors for developing MN are multifactorial. Age is prominent: incidence peaks between 40–60 years, with rare pediatric onset. Male sex confers a 2:1 increased risk compared to females, particularly in primary MN. Ethnicity influences susceptibility—PLA2R-associated MN is more prevalent among Caucasians and Asians than African Americans, who exhibit higher rates of secondary MN, especially linked to SLE or infection. Smoking is an established modifiable risk factor, associated with both increased incidence and poorer renal outcomes, likely via oxidative stress, endothelial dysfunction, and enhanced autoantibody production. Obesity (BMI ≥30 kg/m²) correlates with higher risk and disease progression, potentially through chronic inflammation, adipokine dysregulation, and complement activation. Hypertension and dyslipidemia—common comorbidities in nephrotic syndrome—exacerbate glomerular injury and accelerate fibrosis.

Genetic predisposition plays a significant role. Genome-wide association studies (GWAS) have identified strong HLA class II associations: the *HLA-DQA1* allele (rs2187668) and *HLA-DRB1* variants (e.g., *DRB1*15:01 and *DRB1*03:01) confer markedly increased risk for PLA2R-positive MN. These alleles influence antigen presentation to CD4+ T cells, facilitating autoreactive B-cell activation and anti-PLA2R antibody production. Non-HLA loci—including *IRF4*, *NFKB1*, and *STAT4*—implicate interferon signaling, NF-κB pathway dysregulation, and Th17 differentiation in disease susceptibility. Familial clustering is rare but documented, supporting polygenic inheritance rather than monogenic transmission.

Environmental exposures contribute substantially. Chronic viral infections act as molecular mimics or persistent immune stimuli—HBV integrates into host DNA and expresses surface antigen in podocytes, triggering immune complex formation; HCV induces cryoglobulinemia and direct podocyte injury. Endemic regions with high rates of parasitic infection (e.g., *Plasmodium* spp. in malaria-endemic zones) show elevated secondary MN prevalence. Occupational or environmental mercury exposure—historically linked to Minamata disease—induces podocyte toxicity and immune complex deposition. Air pollution (PM2.5, NO₂) has emerging epidemiologic associations with glomerular disease incidence, possibly via systemic inflammation and endothelial activation. Additionally, gut microbiota dysbiosis may modulate immune tolerance; reduced microbial diversity and altered Firmicutes/Bacteroidetes ratios correlate with autoantibody titers and disease activity in preliminary studies.

In summary, MN results from a convergence of genetic susceptibility (especially HLA-driven autoimmunity), environmental triggers (infections, toxins, malignancy), and host-related risk factors (age, sex, smoking, obesity). Understanding these interrelationships guides diagnostic evaluation—such as PLA2R/THSD7A serology, malignancy screening, and infection workup—and informs personalized risk stratification and therapeutic decisions in nephrology practice.

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults, characterized by immune-mediated thickening of the glomerular basement membrane due to subepithelial immune complex deposition—most frequently involving autoantibodies against the phospholipase A2 receptor (PLA2R) or, less commonly, thrombospondin type-1 domain-containing 7A (THSD7A). As a primary (idiopathic) glomerulopathy in approximately 75–80% of cases—or secondary to autoimmune disorders (e.g., systemic lupus erythematosus), infections (e.g., hepatitis B, syphilis), malignancies (e.g., lung, gastric, or lymphoid cancers), or drugs (e.g., NSAIDs, penicillamine, gold salts)—MN typically follows an indolent, heterogeneous clinical course. Early symptoms are often subtle and nonspecific, contributing to frequent diagnostic delays. Patients may report unexplained fatigue, mild peripheral edema (especially periorbital or ankle swelling upon waking), or transient foamy urine—reflecting asymptomatic proteinuria detected incidentally on routine urinalysis. Weight gain without dietary change, decreased exercise tolerance, or vague abdominal discomfort may also occur but lack specificity. Importantly, hypertension and renal dysfunction are usually absent in early disease; serum creatinine remains normal, and estimated glomerular filtration rate (eGFR) is preserved. Microscopic hematuria may be present in up to 30% of cases but is rarely macroscopic. Because MN predominantly affects podocytes and the filtration barrier—not tubulointerstitial or vascular compartments—early urinary sediment typically shows lipiduria (oval fat bodies), hyaline casts, and occasional granular casts, with minimal dysmorphic red blood cells.

Typical symptoms emerge as proteinuria intensifies (>3.5 g/24 h), fulfilling criteria for nephrotic syndrome. The hallmark is heavy, selective proteinuria—predominantly albumin—with consequent hypoalbuminemia (<3.0 g/dL), generalized edema (anasarca in severe cases), and hyperlipidemia (elevated total cholesterol, LDL, triglycerides, and apolipoprotein B). Edema is often symmetric, pitting, and worsens with prolonged standing or at day’s end; it may involve scrotal or labial swelling and, in advanced cases, pleural effusions or ascites. Patients frequently describe profound fatigue, malaise, and reduced appetite. Foamy or frothy urine becomes persistent and conspicuous. Some report orthostatic hypotension due to intravascular volume depletion from hypoalbuminemia-induced reduction in plasma oncotic pressure. Unlike rapidly progressive glomerulonephritis, MN does not cause acute kidney injury at onset; however, gradual eGFR decline may occur over months to years, particularly in patients with persistent nephrotic-range proteinuria, male sex, older age (>60 years), or baseline impaired renal function.

Accompanying symptoms reflect both the nephrotic state and underlying pathophysiology. Hypercoagulability—driven by urinary loss of antithrombin III, protein S, and protein C, coupled with hepatic overproduction of clotting factors—predisposes to venous thromboembolism (VTE), notably renal vein thrombosis (RVT), which may manifest as sudden flank pain, hematuria, worsening proteinuria, or acute kidney injury. Infections—including spontaneous bacterial peritonitis (SBP), cellulitis, pneumonia, and sepsis—are more frequent due to urinary losses of immunoglobulins and complement components. Patients may experience recurrent upper respiratory tract infections or skin abscesses. Hypovolemic symptoms such as dizziness or postural lightheadedness can occur during aggressive diuretic use or spontaneous salt-wasting. Vitamin D deficiency (due to urinary loss of vitamin D-binding protein) contributes to secondary hyperparathyroidism and bone mineral abnormalities. Rarely, patients develop thyroid dysfunction (e.g., hypothyroidism) linked to autoimmunity or altered thyroid hormone binding.

Complications arise from chronic nephrotic syndrome and disease progression. Approximately 30–40% of untreated idiopathic MN patients experience spontaneous remission within 5 years; however, 25–40% progress to chronic kidney disease (CKD) Stage 3 or higher, and 10–20% reach end-stage kidney disease (ESKD) requiring dialysis or transplantation over 10–15 years. Accelerated atherosclerosis increases cardiovascular morbidity and mortality—myocardial infarction and stroke risk are doubled compared with age-matched controls. RVT may lead to irreversible renal parenchymal damage or pulmonary embolism. Infection-related mortality remains elevated, especially in elderly or immunosuppressed individuals. Post-transplant recurrence occurs in ~30–40% of PLA2R-positive patients, often within the first year, and may precipitate graft loss. Secondary MN carries additional morbidity related to its underlying etiology—e.g., paraneoplastic syndromes in malignancy-associated cases or lupus nephritis flares in SLE.

Diagnosis integrates clinical, laboratory, imaging, and histopathological findings. Urinalysis reveals proteinuria (often 3+ to 4+ on dipstick), lipiduria, and hyaline/granular casts; quantitative assessment includes 24-hour urine protein excretion or urine protein-to-creatinine ratio (UPCR >350 mg/mmol confirms nephrotic-range proteinuria). Serum studies show hypoalbuminemia, hyperlipidemia, elevated serum creatinine (if CKD present), and low complement levels (C3/C4 are typically normal—distinguishing MN from post-infectious or lupus glomerulonephritis). Anti-PLA2R antibody testing (ELISA or chemiluminescence) has >95% specificity and ~70–80% sensitivity for primary MN; anti-THSD7A antibodies are detected in ~1–5% of PLA2R-negative cases. Renal ultrasound demonstrates preserved kidney size and echogenicity (unlike chronic fibrosis); Doppler may identify RVT. Definitive diagnosis requires percutaneous kidney biopsy: light microscopy shows diffuse capillary wall thickening without cellular proliferation; silver methenamine stains reveal characteristic 'spikes' projecting from the basement membrane; immunofluorescence demonstrates global, granular IgG and C3 deposition along capillary loops; electron microscopy confirms subepithelial electron-dense deposits, often with 'moth-eaten' basement membrane remodeling and podocyte foot process effacement.

Differential diagnosis includes other causes of nephrotic syndrome: minimal change disease (MCD) presents similarly but lacks immune deposits on IF/EM and is steroid-responsive in children/young adults; focal segmental glomerulosclerosis (FSGS) shows segmental sclerosis and foot process effacement but no subepithelial deposits; diabetic nephropathy exhibits nodular glomerulosclerosis (Kimmelstiel-Wilson lesions), arteriolar hyalinosis, and long-standing diabetes history; amyloidosis demonstrates Congo red–positive apple-green birefringence and lambda/kappa light chain restriction. Secondary MN must be distinguished from lupus membranous nephropathy (Class V LN), which shows concurrent mesangial or endocapillary proliferation, subendothelial deposits, and positive ANA/dsDNA. Hepatitis B–associated MN shows HBsAg positivity and distinct histologic features (e.g., ground-glass hepatocytes). Accurate classification guides prognosis and therapy—e.g., immunosuppression is indicated for high-risk primary MN but contraindicated in active malignancy-associated MN.

Membranous nephropathy (MN) is an immune-mediated glomerular disease characterized by subepithelial immune complex deposition, leading to thickening of the glomerular basement membrane and clinical manifestations ranging from asymptomatic proteinuria to nephrotic syndrome. It is the most common cause of primary nephrotic syndrome in adults. Management requires a risk-stratified, individualized approach integrating clinical, histopathological, and serological data—including anti-PLA2R and anti-THSD7A antibody titers—to guide therapeutic decisions. Treatment strategies fall broadly into conservative management, pharmacologic immunosuppression, and supportive care; surgical intervention has no role in MN, as it is not amenable to resection or bypass.

Conservative treatment forms the cornerstone for low-risk patients—typically those with persistent proteinuria <4 g/day, stable estimated glomerular filtration rate (eGFR), and absence of hypertension or edema. This includes strict blood pressure control targeting <130/80 mmHg using angiotensin-converting enzyme inhibitors (ACEi) or angiotensin II receptor blockers (ARBs), which reduce intraglomerular pressure and proteinuria independently of antihypertensive effects. Dietary sodium restriction (<2 g/day) enhances diuretic efficacy and mitigates volume overload. Statin therapy is recommended for all patients with nephrotic-range proteinuria to manage dyslipidemia and confer potential renoprotective benefits. Smoking cessation, weight optimization, and influenza/pneumococcal vaccination are essential components of long-term renal protection. Approximately 30% of untreated patients experience spontaneous remission within 5 years, underscoring the appropriateness of initial observation in carefully selected cases.

Pharmacologic therapy is indicated for high-risk patients: those with persistent proteinuria ≥4 g/day for >6 months, declining eGFR (>15% decline/year), or progressive hypoalbuminemia (<2.5 g/dL). First-line immunosuppression follows evidence-based protocols. The Ponticelli regimen—alternating monthly cycles of oral prednisone and intravenous cyclophosphamide—is historically effective but carries significant gonadal toxicity, hemorrhagic cystitis, and malignancy risks. Contemporary guidelines increasingly favor rituximab, a chimeric anti-CD20 monoclonal antibody. The MENTOR trial demonstrated superior complete remission rates (65% vs. 19%) and improved safety over cyclosporine at 24 months, establishing rituximab as first-line for PLA2R-positive MN. Dosing typically involves two 1-g infusions separated by 2 weeks or four weekly 375 mg/m² doses; repeat dosing is guided by CD19+ B-cell repopulation and anti-PLA2R titer trends. For rituximab-ineligible or refractory patients, calcineurin inhibitors (tacrolimus or cyclosporine) combined with low-dose corticosteroids remain viable alternatives, though require vigilant monitoring for nephrotoxicity, hypertension, and new-onset diabetes. Mycophenolate mofetil (MMF) shows modest efficacy in small trials but lacks robust comparative data and is generally reserved for contraindications to first-line agents. Emerging therapies—including anti-BAFF agents (e.g., belimumab) and complement inhibitors (e.g., iptacopan)—are under active investigation in phase II/III trials.

Surgical treatment has no established indication in membranous nephropathy. MN is a systemic autoimmune disorder affecting glomerular capillary walls—not a localized structural lesion—and therefore cannot be corrected via nephrectomy, shunt placement, or transplantation as primary therapy. Kidney transplantation may be considered in end-stage kidney disease (ESKD), but recurrence rates exceed 30%, particularly in PLA2R-positive recipients. Pre-transplant anti-PLA2R titer reduction and post-transplant rituximab prophylaxis are being explored to mitigate recurrence risk.

China offers distinct advantages in MN management, rooted in integrated clinical infrastructure, large-scale biomarker validation, and innovative therapeutic implementation. Chinese nephrology centers have pioneered real-world validation of anti-PLA2R assays across diverse ethnic cohorts, refining risk prediction models applicable to Asian populations. National registries such as the China Chronic Kidney Disease (C-CKD) Network enable longitudinal outcome tracking and rapid dissemination of best practices. Rituximab is widely accessible and reimbursed under China’s National Reimbursement Drug List (NRDL), significantly improving affordability compared to Western markets. Moreover, China leads in pragmatic trials evaluating abbreviated rituximab regimens and biosimilar rituximab—demonstrating non-inferior efficacy and enhanced cost-effectiveness without compromising safety. Traditional Chinese Medicine (TCM) adjuncts, such as tripterygium glycosides (Lei Gong Teng), are used in select centers under rigorous quality control; meta-analyses suggest synergistic proteinuria reduction when combined with low-dose steroids, though hepatotoxicity and gonadal suppression necessitate close monitoring. Multidisciplinary nephrology teams—including dietitians, pharmacists, and TCM specialists—facilitate holistic, patient-centered care aligned with national chronic disease management standards.

Recovery and long-term follow-up emphasize sustained remission monitoring and complication prevention. Patients achieving remission require quarterly assessment of urine protein-to-creatinine ratio (UPCR), serum albumin, creatinine, and anti-PLA2R titers for at least 3 years; relapse is defined as UPCR >3.5 g/g after confirmed remission. Blood pressure and lipid profiles must be maintained within target ranges indefinitely. Vaccination status—particularly pneumococcal, hepatitis B, and annual influenza—should be updated pre- and post-immunosuppression. Patients on rituximab require screening for hepatitis B virus (HBV) reactivation and baseline immunoglobulin levels to identify hypogammaglobulinemia risk. Lifestyle counseling remains critical: moderate-intensity aerobic exercise (150 min/week), plant-predominant low-sodium diets, and avoidance of NSAIDs and contrast media unless absolutely necessary. Psychosocial support is integral—nephrotic syndrome imposes substantial emotional burden, and depression/anxiety screening should be routine. Finally, women of childbearing potential require preconception counseling regarding teratogenic risks of immunosuppressants and optimal timing for pregnancy (ideally after sustained remission >12 months off cytotoxic agents). With contemporary risk-adapted strategies, over 70% of patients achieve partial or complete remission within 2–3 years, preserving native kidney function and markedly reducing progression to ESKD.