Membranoproliferative glomerulonephritis (MPGN) is one of those “Step classic” diagnoses that can feel like a histology-first rabbit hole—until you connect it to complement pathways, hepatitis, and cryoglobulins. Once you see MPGN as a pattern of injury (not a single disease), the pathology slides and lab clues start to line up fast.
Where MPGN fits in glomerular disease (Step framework)
MPGN is a nephritic or mixed nephritic–nephrotic syndrome characterized by:
- Glomerular hypercellularity (often mesangial + endocapillary)
- Thickened capillary walls
- Complement activation with immune deposits or complement dysregulation
Typical presentation buckets:
- Nephritic signs: hematuria, RBC casts, hypertension, azotemia
- Nephrotic features often present too: proteinuria (can be heavy), edema, hypoalbuminemia
First Aid cross-ref (Renal—Glomerular diseases): MPGN is associated with “tram-track” GBM appearance, subendothelial deposits, and HBV/HCV associations.
Definition (what you’re actually diagnosing)
Membranoproliferative GN is a histopathologic pattern of glomerular injury marked by:
- Mesangial proliferation
- GBM remodeling (duplication/splitting)
- Capillary wall thickening
- Often immune complex and/or complement deposition
Clinically, MPGN often presents as a mixed nephritic–nephrotic syndrome.
Pathophysiology (the key Step 1 mental model)
The unifying concept: “Why the tram-tracks?”
The hallmark “tram-track” appearance comes from GBM duplication due to:
- Subendothelial deposits and inflammation
- Mesangial cell interposition between endothelium and GBM
- New basement membrane formation as the glomerulus tries to “wall off” injury
Modern classification (more useful than old Type I/II/III for boards)
MPGN is best thought of in two mechanistic categories:
- Immune complex–mediated MPGN
- Driven by chronic antigenemia → immune complex deposition → classical complement activation
- Common triggers:
- Hepatitis C (often with mixed cryoglobulinemia)
- Hepatitis B
- Chronic infections (e.g., endocarditis)
- Autoimmune disease (e.g., SLE can produce an MPGN pattern)
- Complement-mediated MPGN (C3 glomerulopathy spectrum)
- Due to alternative complement pathway dysregulation
- Leads to dominant C3 deposition with little/no immunoglobulin
- Classic related entity: dense deposit disease (historically “MPGN type II”)
Classic associations (very high-yield)
Hepatitis C and cryoglobulinemia
MPGN (immune complex–mediated) is strongly associated with HCV, often via mixed cryoglobulinemia.
Clues for cryoglobulinemia (Step 2 style):
- Palpable purpura
- Arthralgias, weakness
- Neuropathy
- Low complement (especially low C4)
- Renal disease: hematuria + proteinuria (MPGN pattern)
Hepatitis B
HBV can also drive immune complex MPGN (and membranous nephropathy—know both).
Complement dysregulation (C3 glomerulopathy)
Think: persistent alternative pathway activation → low C3 (often) and C3-dominant deposits.
Clinical presentation (what the stem gives you)
Symptoms/signs
- Hematuria (cola/tea-colored urine may be described)
- Periorbital or peripheral edema
- Hypertension
- Fatigue from renal dysfunction
Labs
- Elevated BUN/Cr (variable)
- Urinalysis: RBCs, RBC casts, proteinuria
- Complement:
- Often low C3 (immune complex or complement-mediated)
- Cryoglobulinemia often has low C4 as well
Syndrome pattern
- MPGN often looks nephritic, but don’t be surprised by significant proteinuria.
Diagnosis (how Step questions “prove” MPGN)
Light microscopy (LM)
- Hypercellular glomeruli (mesangial and endocapillary proliferation)
- Thickened capillary walls
- “Tram-track” appearance from GBM duplication/splitting
Immunofluorescence (IF): helps separate mechanisms
| MPGN mechanism | IF pattern | Complement notes |
|---|---|---|
| Immune complex–mediated | Granular deposits of IgG/IgM + C3 along capillary walls/mesangium | Often low C3 (± low C4 depending on trigger) |
| Complement-mediated (C3 glomerulopathy) | C3-dominant staining with minimal immunoglobulin | Often low C3 from alternative pathway activation |
Electron microscopy (EM): where deposits live
- Classically: subendothelial deposits (immune complex MPGN)
- Dense deposit disease: intramembranous “dense” ribbon-like deposits (classic board image association)
Step 1 deposit location anchor:
- Subepithelial = post-strep, membranous (“spike and dome”)
- Subendothelial = MPGN, lupus (“wire loop”)
- Mesangial = IgA nephropathy
MPGN = subendothelial is the key association.
Differentials you must separate quickly
MPGN vs Poststreptococcal GN (PSGN)
Both can be nephritic with low complement. Differentiate with deposits:
| Feature | MPGN | PSGN |
|---|---|---|
| EM deposits | Subendothelial | Subepithelial humps |
| LM | Tram-tracks, hypercellular | Hypercellular glomeruli |
| Associations | HBV/HCV, cryoglobulins, complement dysregulation | Recent strep infection (pharyngitis/impetigo) |
MPGN vs Lupus nephritis
- Lupus can produce an MPGN-like pattern, but lupus often has “full house” IF (IgG, IgA, IgM, C3, C1q) and systemic SLE clues.
Treatment (Step 2–relevant, mechanism-based)
Treatment depends on whether it’s immune complex–mediated or complement-mediated, plus how severe the disease is.
General principles
- Control blood pressure and proteinuria: ACE inhibitor/ARB
- Manage edema: diuretics, salt restriction
- Address complications of CKD if present
Immune complex–mediated MPGN
- Treat the underlying cause
- HCV: direct-acting antivirals (DAAs)
- HBV: antivirals (e.g., entecavir/tenofovir in appropriate settings)
- Treat chronic infections (e.g., endocarditis)
- Consider immunosuppression in select cases (often nephrology-guided), especially if rapidly progressive features exist
Cryoglobulinemic vasculitis with renal involvement (common HCV tie-in)
- Treat HCV + consider immunosuppression (e.g., rituximab ± steroids) depending on severity
(The exam loves the concept: remove the antigen drive + control immune injury.)
Complement-mediated MPGN (C3 glomerulopathy)
- Supportive renal care is foundational
- Selected patients may receive targeted therapy (specialist-driven; complement inhibitors in certain contexts)
High-yield “buzzwords” and associations (rapid recall)
- “Tram-track” GBM = MPGN
- Subendothelial deposits (classic)
- HBV/HCV association
- Cryoglobulinemia → MPGN (often HCV)
- Low complement (often low C3; cryoglobulinemia often low C4 too)
- Think mixed nephritic–nephrotic presentation
Step-style mini cases (what you should recognize instantly)
Vignette 1
A patient with chronic hepatitis C has palpable purpura and hematuria; complement levels are low; biopsy shows tram-tracks.
Answer: Immune complex–mediated MPGN due to HCV-associated cryoglobulinemia.
Vignette 2
Child/adult with hematuria + proteinuria; IF shows C3 dominant staining with minimal immunoglobulin.
Answer: Complement-mediated MPGN (C3 glomerulopathy spectrum).
First Aid cross-references (what to flip to)
In First Aid (Renal → Nephritic/nephrotic syndromes / Glomerular diseases), MPGN is typically summarized with:
- Tram-track appearance
- Subendothelial deposits
- HBV/HCV associations
- Complement involvement (especially in dense deposit disease)
Use FA to anchor the buzzwords, then use this rule to solve questions:
IF tells you mechanism (immune complexes vs C3-only); EM tells you location; LM tells you pattern (tram-tracks).