Case 35: Diagnosis & Conclusions

Diagnosis: Phospholipase-A2-Receptor (PLA2R) Positive Membranous Nephropathy (or Primary/Idiopathic Membranous Nephropathy)

Case Summary:

In this case, we find an older man who presents with only lower extremity edema. This symptom can be a sign of proteinuria, and as we soon discover on urinalysis, this patient has 4+ protein on dipstick. It is crucial to quantify the proteinuria, as the dipstick gives us only an estimate and only detects albuminuria.  Our patient has a urine protein:creatinine ratio of 8700mg/g, or nephrotic range proteinuria. 

Nephrotic range proteinuria is defined as greater than 3 to 3.5 grams of protein in a 24-hour urine collection, or a urine protein:creatinine ratio of greater than 3000 to 3500 mg/g. Together, proteinuria, significant edema, hypoalbuminemia, and often hyperlipidemia/lipiduria (lipids in the urine) comprise nephrotic syndrome. Our patient meets criteria for nephrotic syndrome.

What is the differential diagnosis for nephrotic syndrome?
Primary causes of nephrotic syndrome
Focal segmental glomerulosclerosis (FSGS)
Membranous nephropathy
Minimal change disease
Secondary causes of nephrotic syndrome
Diabetes mellitus (most common)
Systemic lupus erythematosus (SLE)
Hepatitis B or C (more commonly HBV)
Nonsteroidal anti-inflammatory drugs
HIV
Amyloidosis
Multiple myeloma
Preeclampsia

Now that we have established a broad differential for nephrotic syndrome, let’s try to determine which etiology is most likely in our patient. His clinical presentation, basic laboratory studies, and urinalysis are consistent with nephrotic syndrome but are otherwise unrevealing. We must move to a kidney biopsy to confirm our diagnosis.

Light microscopy and electron microscopy show us thickening of the basement membrane and subepithelial deposits – together, these findings raise suspicion for membranous nephropathy (MN). With focal segmental glomerulosclerosis (FSGS), we would look for areas of sclerosis in some glomeruli. Minimal change disease is also ruled out here, as we would except only podocyte effacement on electron microscopy without light microscopy changes or immune-complex deposits.

MN, like many glomerular diseases, can be primary or secondary (caused by another underlying disease). Distinguishing between primary and secondary glomerular diseases is critical, as this will determine the treatment. We can use the patient’s clinical history, serologic testing, and immunofluoresence (IF) to try to tell the difference.

In primary MN, we expect to find a granular pattern basement membrane staining of IgG and C3 on IF, and the presence of the phospholipase A2 receptor antigen (PLA2R) or thrombospondin type-1 domain-containing 7A (THSD7A) within immune deposits (with PLA2R being more common). PLA2R antibodies can be detected in the serum of primary MN patients, with specificity being near 100%.

What about secondary causes?
The differential includes:
 Malignancy, typically solid tumors
Systemic lupus erythematosus (SLE) nephritis
Drugs (i.e. penicillamine, anti-tumor necrosis factor (TNF) antibodies, nonsteroidal anti-inflammatory drugs (NSAIDs))
Syphilis
Hepatitis C virus, Hepatitis B virus (HBV more common)
Immunoglobulin-G4 (IgG4) disease
Let’s review the classic histopathological findings seen in membranous nephropathy (primary or secondary):
Light Microscopy
Diffuse thickening of the glomerular basement membrane (GBM), best seen on the Periodic-Acid Schiff or PAS stain.
Jones Silver Stain
Jones silver stain (below) stains collagen and the basement membrane a dark color, but does not stain immune-complex deposits. Thus, “spikes” of basement membrane can be seen around the “holes” of the basement membrane deposits.
Electron Microscopy (EM)
In either primary or secondary MN, subEPIthelial dense deposits are found within the basement membrane that are visualized closer to the podocyte (podocyte = visceral EPIthelial cell). Mesangial deposits (and less commonly subendothelial deposits) may also be seen with certain secondary causes of membranous nephropathy.
Immunofluorescence (IF)
Granular pattern staining of IgG and C3
The diagnosis clinchers here are the immunofluoresence (IF) or immunohistochemistry (IHC) stains for primary membranous nephropathy antigens. Click below to take a look at a couple images.
IHC for PLA2R
IF for PLA2R

The disease course and treatment? The classic teaching is that 1/3 of patients will go into spontaneous remission, 1/3 will remain stable, and 1/3 will progress. For those patients at moderate to high risk of progression (more than 4 g proteinuria/24 hours), the treatment is Immunosuppressive therapy.  Options include alternating corticosteroids and cyclophosphamide (modified Ponticelli protocol), calcineurin inhibitors (cyclosporine or tacrolimus), or rituximab. Patients should also be treated with angiotensin inhibitors. The MENTOR study, published in 2019, found that treatment with cyclosporine was noninferior to rituximab – though there was no cyclophosphamide arm in this study. In one small randomized study of 32 patients, adrenocorticotropic hormone (ACTH) was shown to be effective when compared to cytotoxic drugs. Anti-PLA2R autoantibody levels can be measured to monitor disease activity and response to therapy. Higher antibody levels may be associated with increased risk of disease recurrence after kidney transplantation.

Case 35 Index
Case 35 Introduction
Case 35 Physical Exam
Case 35 Diagnostic Testing
Case 35 Pathology
Case 35 Additional Pathology
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