Membranous Nephropathy

The contract between this chapter and the reader.

1. 1. Define membranous nephropathy and its immune-complex mechanism.
2. 2. Distinguish primary (anti-PLA2R) from secondary causes.
3. 3. Recognise the clinical presentation and thrombosis risk.
4. 4. Diagnose with anti-PLA2R and biopsy.
5. 5. Risk-stratify and decide treat versus watchful waiting.
6. 6. Provide supportive therapy, including anticoagulation.
7. 7. Treat high-risk disease with immunosuppression.
8. 8. Use anti-PLA2R to monitor.
9. 9. Understand the prognosis (the rule of thirds) and the evidence.

A sixty-second reading. Each bullet stands alone.

• Membranous nephropathy is the classic immune-complex cause of adult nephrotic syndrome.
• Subepithelial immune deposits thicken the basement membrane and injure podocytes.
• Primary disease is autoimmune — antibody to the podocyte antigen PLA2R in most cases.
• Secondary causes include malignancy, hepatitis B, drugs, and lupus.
• It presents as an adult nephrotic syndrome and carries the highest thrombosis risk of the nephrotic diseases.
• Anti-PLA2R antibody supports the diagnosis, monitors activity, and can sometimes avoid biopsy.
• Biopsy shows subepithelial deposits, granular IgG/C3, and basement-membrane spikes.
• The “rule of thirds” — roughly a third remit spontaneously, a third persist, a third progress.
• Treatment is risk-stratified: low-risk disease is managed with supportive care and watchful waiting.
• High-risk disease (heavy proteinuria, declining function, high anti-PLA2R) is treated with immunosuppression.
• Rituximab is often first-line immunosuppression; cyclophosphamide-steroid regimens and calcineurin inhibitors are alternatives.
• Supportive care includes RAAS blockade, a statin, and anticoagulation for the thrombosis risk.
• The anti-PLA2R titre tracks disease activity and falls before proteinuria improves.

The medical core. An expert should agree membranous nephropathy is fully covered here.

Why it matters at the bedside

Membranous nephropathy is the disease the discovery of one antibody transformed. Once a black box of ‘idiopathic’ adult nephrotic syndrome, it is now a disease you can diagnose, monitor, and sometimes treat from a blood test — anti-PLA2R. And its natural history is forgiving enough that the hardest decision is often not which drug, but whether to treat at all.

What it is and the immune-complex mechanism

• Membranous nephropathy is the classic immune-complex nephrotic disease of adults. Antibody forms immune complexes in situ on the outer (subepithelial) aspect of the glomerular basement membrane; these deposits drive basement-membrane thickening (the ‘spikes’ of new matrix between deposits) and complement-mediated podocyte injury, producing heavy proteinuria. It is the granular-immunofluorescence, subepithelial-deposit disease of the first chapter made clinical.

Primary versus secondary

• The pivotal distinction is primary versus secondary. Primary (autoimmune) membranous is, in about seventy per cent of cases, driven by an antibody to the podocyte antigen PLA2R (with anti-THSD7A in a smaller subset), typically IgG4. Secondary membranous is the same lesion provoked by another process — malignancy (especially in older patients), hepatitis B, drugs such as NSAIDs, or lupus (membranous lupus, class V). Treating the underlying cause is the key in secondary disease.

Clinical presentation and thrombosis risk

• It presents as an adult nephrotic syndrome, often with heavy proteinuria and an insidious onset. Its defining complication is thrombosis: membranous carries the highest thrombosis risk of all the nephrotic diseases — including renal vein thrombosis — a risk that rises as the albumin falls and that shapes the supportive management.

Diagnosis: anti-PLA2R and biopsy

• Diagnosis rests on two pillars. The anti-PLA2R antibody supports a diagnosis of primary disease, monitors its activity, and in the right clinical setting can even allow biopsy to be deferred. The biopsy itself is characteristic: basement-membrane thickening with spikes on silver-stained light microscopy, granular IgG and C3 on immunofluorescence, and subepithelial deposits on electron microscopy, with PLA2R antigen demonstrable in the deposits.

The rule of thirds and risk stratification

• The natural history is captured by the ‘rule of thirds’: roughly a third of patients remit spontaneously, a third have persistent but stable proteinuria, and a third progress toward kidney failure. Because spontaneous remission is common, treatment is risk-stratified — by the degree of proteinuria, the kidney function and its trajectory, and the anti-PLA2R level — into low, moderate, high, and very-high-risk groups.

Treat versus watchful waiting

• This stratification drives the central decision. Low-risk patients — preserved function, lower proteinuria, stable — are managed with supportive care and watchful waiting, because many will remit without immunosuppression. High-risk patients — heavy proteinuria, declining function, high anti-PLA2R — are treated with immunosuppression. The moderate-risk group is the judgement zone, treated if they fail to improve. The principle is to spare the self-limiting and treat the progressive.

Supportive therapy

• Supportive therapy underpins all management: RAAS blockade to reduce proteinuria and intraglomerular pressure, a statin for hyperlipidemia, diuretics for oedema, and — distinctively in membranous — anticoagulation, given the high thrombosis risk, particularly when the albumin is low. It is the foundation on which watchful waiting rests and to which immunosuppression is added.

Immunosuppression for high-risk disease

• When immunosuppression is warranted, the options have a strong evidence base. Rituximab (anti-CD20) is now often first-line and depletes the B cells making the pathogenic antibody; the alternating cyclophosphamide-and-steroid (Ponticelli) regimen is highly effective; and calcineurin inhibitors are an alternative, though relapse on withdrawal is common. The anti-PLA2R titre helps select and follow the response.

Monitoring with anti-PLA2R

• Anti-PLA2R is not only diagnostic but a genuine activity biomarker: its titre tracks the disease, and — importantly — it falls before the proteinuria improves, so an immunological remission (disappearing antibody) precedes and predicts the clinical remission (falling proteinuria). It guides when to treat, whether treatment is working, and the risk of relapse.

Prognosis and the evidence

• The evidence is rich and practice-shaping: the rule of thirds justifies watchful waiting in low-risk disease; rituximab has proven non-inferior or superior for sustained remission (the MENTOR trial); the cyclophosphamide-steroid regimen has long-term efficacy data; anti-PLA2R has been validated as a diagnostic and monitoring biomarker; and membranous can recur after transplantation, where anti-PLA2R again signals it. The disease is now among the best-understood of the glomerulonephritides.

Five fully-built tables.

Table A — The disease at a glance

Table B — Primary versus secondary

Table C — Diagnosis

Table D — Risk stratification and treatment

Table E — Immunosuppression options

Visualise & Map

Causal chains, each ending in a named action.

Chain 1 — The autoantibody

Anti-PLA2R binds the podocyte antigen → subepithelial immune complexes and complement activation → podocyte injury and proteinuria → ACTION: immunosuppress when the risk is high.

Chain 2 — The subepithelial signature

Deposits form on the outer membrane → spikes of new matrix and granular IgG → the characteristic biopsy → ACTION: confirm with light, immunofluorescence, and electron microscopy.

Chain 3 — The thrombotic state

Heavy proteinuria and a low albumin → a profoundly hypercoagulable state → the highest thrombosis risk of the nephrotic diseases (renal vein thrombosis) → ACTION: anticoagulate, especially with a low albumin.

Chain 4 — The forgiving course

The rule of thirds → about a third remit spontaneously → immunosuppression is not always needed → ACTION: watchful waiting in low-risk disease.

Chain 5 — The biomarker

Anti-PLA2R reflects disease activity → its titre falls before the proteinuria improves → immunological remission precedes clinical remission → ACTION: monitor the titre to guide and follow treatment.

Numbered rules. These numbers are the cross-reference handle for the cases and flowcharts.

Clinical Reasoning

Five cases. Each stops you at a decision before it answers it.

Every mechanism from Level 3 earns a bedside consequence and an action.

Exhaustive. Every rule in the chapter is here.

Safety & Evidence

Panel A — Red flags

Panel B — NEVER DO

Anti-patterns clinicians fall into. Each becomes a Level 22 distractor.

The grade reflects strength of evidence, not importance.

Patient Decisions

Outcomes as natural frequencies. Figures are representative; the direction of effect is given where precise numbers are uncertain.

Apply & Test

Copy-paste chart notes that map to the real decisions in this chapter.

Template 1 — Membranous diagnosis / risk-stratification note

• Presentation: adult nephrotic syndrome; proteinuria; albumin ___.
• Anti-PLA2R: positive/negative; titre ___.
• Biopsy: subepithelial deposits, granular IgG, spikes ___.
• Primary vs secondary: malignancy / hepatitis B / lupus / drugs screened ___.
• Risk category: low / moderate / high / very high ___.

Template 2 — Treatment / monitoring note

• Strategy: watchful waiting (low-risk) / immunosuppression (high-risk) ___.
• Immunosuppression (if used): rituximab / cyclophosphamide-steroid / CNI ___.
• Supportive: RAAS, statin, anticoagulation (thrombosis risk) ___.
• Monitoring: anti-PLA2R titre; proteinuria ___.
• Secondary cause treated (if applicable): ___.

Pre-rounds compression. Rules only.

Active recall. At least one card per objective.

Micro-teaching for rounds. Two scenarios, five steps each.

Metacognition anchored to this chapter's tensions. No answers provided.

1. 1. A third of patients remit without treatment; how do you decide whom to spare immunosuppression and whom to commit to it, knowing the future is uncertain?
2. 2. Anti-PLA2R falls before proteinuria does; how much should an immunological remission, ahead of the clinical one, drive your decisions?
3. 3. The thrombosis risk is real but so is the bleeding risk of anticoagulation; where do you set the albumin threshold to anticoagulate?
4. 4. How hard should you hunt for an occult malignancy in an anti-PLA2R-negative older patient, and when does the search itself become the harm?
5. 5. With a non-invasive antibody that can diagnose and monitor, when is a biopsy still worth its risk — and when can serology stand alone?

Nine items, each anchored in this chapter. At least one per objective.