Clinical Case Analysis

Patient Summary

Diagnosis: Membranous Nephropathy (MN) with Nephrotic Syndrome

Biopsy Findings in MN

• Light microscopy: Diffuse capillary wall thickening without hypercellularity
• Immunofluorescence: Granular IgG + complement along GBM
• Electron microscopy: Subepithelial deposits → "spike and dome" pattern

Critical Flag: The L1 Wedge Compression Fracture

• Markedly elevated ESR (95)
• Vertebral compression fracture (L1)
• Nephrotic syndrome

Malignancies account for 6–22% of secondary MN cases. These include carcinoma of the bronchus, breast, colon, stomach, ovary, kidney, pancreas, and prostate, as well as Hodgkin disease. — Brenner and Rector's The Kidney

In cancer-associated MN, the kidney biopsy may show increased inflammatory infiltrate (>8 cells/glomerulus) in 92% of cases vs. 25% in idiopathic MN. IgG subclass analysis shows IgG1/IgG2 predominance (versus IgG4 in primary/idiopathic MN).

• Anti-PLA2R positive → primary (idiopathic) MN
• Anti-PLA2R negative + THSD7A positive → strongly suspect malignancy. In one cohort, 8 of 40 THSD7A-positive MN patients developed malignancy within a median of 3 months of diagnosis.

Differential Diagnosis for Secondary MN

Workup to Perform

1. Anti-PLA2R antibody (serum) — differentiates primary from secondary MN
2. Anti-THSD7A antibody — if PLA2R negative
3. ANA, anti-dsDNA, complement (C3/C4) — exclude SLE (class V lupus nephritis)
4. HBsAg, anti-HCV, VDRL/RPR — infectious causes
5. Serum protein electrophoresis / SIFE — paraproteinemia, myeloma
6. Bone scan / MRI spine — characterize L1 lesion (lytic vs. osteoporotic vs. pathological fracture)
7. Low-dose CT chest — lung malignancy
8. Age-appropriate cancer screening — colonoscopy, PSA, mammography
9. Serum albumin — quantify nephrotic state and thrombotic risk stratification

Management

Non-Immunosuppressive (All Patients)

• RAAS blockade (ACE inhibitor or ARB): reduces proteinuria and BP — first-line regardless of BP
• Sodium restriction <2 g/day
• Statins: for dyslipidemia (elevated total cholesterol, LDL in nephrotic syndrome)
• Anticoagulation: Albumin <2.8 g/dL is the strongest predictor of venous thromboembolism. With albumin 2–3 g/L → aspirin 81 mg; albumin <2 g/L or PCR >10 g/g → consider prophylactic anticoagulation
• Loop diuretics: for edema and pleural effusions

Risk Stratification for Immunosuppression

Immunosuppressive Options

1. Ponticelli Protocol (cyclophosphamide + steroids): IV methylprednisolone 1 g on days 1–3 of months 1, 3, 5; oral methylprednisolone on remaining days; alternating with oral cyclophosphamide 2.5 mg/kg/day in months 2, 4, 6. Superior long-term outcomes; cyclophosphamide preferred over chlorambucil.
2. Rituximab (anti-CD20): Now the favored first-line agent in moderate-risk patients and many high-risk patients. The MENTOR trial showed rituximab superior to cyclosporine for sustained remission. The RI-CYCLO trial directly compared rituximab to the cyclophosphamide regimen — evidence continues to evolve.

However, if secondary MN due to malignancy is confirmed, immunosuppression should be withheld until the underlying malignancy is treated. Tumor resection/remission can lead to complete remission of nephrotic syndrome.

Summary

Malignancy Workup in Membranous Nephropathy

Why This Patient is High-Risk

Workup — Organized by System

1. Serology (First-Line — Mandatory)

The L1 compression fracture combined with high ESR and nephrotic syndrome mandates myeloma exclusion as a priority.

2. Imaging

3. Gender- and Age-Appropriate Cancer Screening

4. Tumor Markers (Targeted)

5. Hematologic Malignancy Workup

6. Biopsy Re-review (Pathology)

• IgG subclass staining — IgG1/IgG2 (malignancy) vs. IgG4 (primary MN)
• Inflammatory cell count per glomerulus — >8 cells favors malignancy-associated MN (92% sensitivity)
• Anti-PLA2R staining on tissue — negative staining supports secondary cause
• NELL1 staining — newer antigen identified in malignancy-associated MN

Key Principle

"A search for malignancy should be undertaken in older patients with newly diagnosed MN after excluding other secondary causes. The presence of anti-THSD7A antibody, absence of anti-PLA2R antibody, and/or predominant IgG1 and IgG2 deposits are other reasons to exclude malignancies thoroughly." — Brenner and Rector's The Kidney

"In those patients in whom no malignancy is found on initial screening, follow-up vigilance for possible cancer should be maintained because cancers have been detected up to 5 years after the initial diagnosis of MN." — Brenner and Rector's The Kidney

Priority Order for This Patient

1. Myeloma screen first — SPEP, SIFE, UIFE, serum free light chains, serum calcium, skeletal survey/MRI spine
2. Anti-PLA2R + anti-THSD7A — serologic pivot point
3. Low-dose CT chest — lung malignancy
4. PSA/mammography — gender-appropriate
5. Colonoscopy / tumor markers — if above negative
6. Bone marrow biopsy — if paraprotein found or myeloma suspected

Malignancy Workup — 70-Year-Old Male with MN

Why Age Matters Here

"In patients older than 60 years, MN is associated with a malignancy in 20–30% of patients." — Brenner and Rector's The Kidney

"The standardized incidence ratio of cancer in male patients with MN was 9.8 compared to the general population. The most common malignancies were lung and prostate. In almost half the patients, the tumor was asymptomatic and detected only because of diagnostic workup for MN." — Brenner and Rector's The Kidney

"Patients with MN who developed cancer were significantly older (65 vs. 52 years; p<0.001)."

Priority Workup for This 70M

Step 1 — Serology (Pivot Tests)

Step 2 — Gender/Age-Specific in a 70-Year-Old Male

Step 3 — Vertebral Lesion Workup (L1 Compression)

Step 4 — Targeted Tumor Markers in a 70M

Step 5 — Biopsy Pathology Re-review

• IgG subclass — IgG1/IgG2 (malignancy) vs. IgG4 (primary MN)
• Inflammatory cell count/glomerulus — >8 cells in 92% of cancer-associated MN
• PLA2R tissue staining — negative = secondary
• NELL1 antigen (newer marker linked to malignancy-associated MN)

Summary Algorithm for This Patient

70M + MN + L1 compression + ESR 95 + Hb 8.6
         │
         ▼
Anti-PLA2R + THSD7A serology
         │
    ┌────┴──────┐
  Negative     Positive (IgG4, PLA2R+)
    │                    │
Malignancy          Primary MN
workup URGENT       conservative Rx
    │
    ▼
Myeloma screen (SIFE, free light chains, MRI spine)
    +
PSA + CT chest (lung)
    +
CECT abdomen review (renal cell, gastric, pancreatic)
    +
Colonoscopy / upper GI scope