Evolution of PLA2R as biomarker, diagnostic tool and prognostic indicator in Membranous Nephropathy

Membranous nephropathy is among the most common causes of the nephrotic syndrome in non-diabetic adult. It is an immune complex mediated disease which occurs when circulating antibodies permeate the glomerular basement membrane and form immune complexes with epitopes on podocyte membranes. Complement activation occurs and results in sublytic levels of C5b-C9 complexes resulting in release of oxidants and proteases that damage the underlying GBM.

Although the majority of MN falls under the idiopathic category ~ 75%, it is important to eliminate secondary causes where relevant as this distinction has important clinical implications; treatment of secondary nephropathy relies on treatment of the underlying disease process whereas idiopathic MN is treated using steroids and/or cytotoxic agents depending on risk of progression.

PLA2R is expressed on the cell body of podocytes near the foot processes. It undergoes constitutive endocytic recycling at the plasma membrane, providing a constant source of PLA2R. Upon binding of PLA2R antibodies, immune complexes aggregate and are shed into the subepithelial space.  The identification of M-type PLA2R as the major target antigen in idiopathic membranous nephropathy in adults by Beck et al represented a paradigm shift in the diagnosis of MN. 70-80% of their patient population with idiopathic MN, but not those with secondary MN or controls, had circulating anti-PLA2R autoantibodies with a specificity is close to 90%–95% (see RFN coverage).  

Staining of kidney biopsy specimens either by immunofluorescence or immunohistochemistry provides an assay by which to identify PLA2R associated MN. Detection of PLA2R in subepithelial deposits in kidney tissue is both a sensitive (69 to 84% across various studies) and specific (close to 100%) technique to diagnose MN. The rate of concordance between tissue PLA2R testing and serological PLA2R testing is variable among studies. One study showed 98% of tissue positive PLA2R patients were also seropositive. Other studies have shown less concordance and have generally found tissue testing more sensitive than serologic testing. Tissue deposits may persist even after serum antibody levels decline and it has been shown that 74% of PLA2R tissue positive patients were seropositive if the sample was taking during a period of heavy proteinuria as opposed to only 32% of patients being seropositive if samples were taken at time of complete or partial remission. Tissue testing is of particular relevance early in the disease course; at this stage circulating anti PLA2R antibodies may not be detectable because the kidney acts as a “sink”, absorbing antibodies. In these instances, PLA2R will be detectable on immunofluorescence staining but serum antibodies will be negative. With disease progression, renal tissue becomes saturated with anti-PLA2R antibodies and becomes seropositive and therefore can be used as a diagnostic and serological biomarker. As patients enter immunologic remission, anti-PLA2R remits in the circulation however proteinuria persists and it is likely that these patients would remain tissue positive if a renal biopsy were to be repeated.

Much research focus has shifted to serum anti-PLA2R antibodies and their diagnostic and putative roles as a biomarker of disease activity in primary MN. There are two standardised test systems for the qualitative and quantitative detection of anti-PLA2R autoantibodies: Anti-PLA2R IIFT and Anti-PLA2R ELISA.  Studies a have shown a relationship between the presence and level of anti-PLA2R antibodies and disease activity. Immunologic remission usually precedes clinical remission by several months. This has particularly important treatment implications in that monitoring of PLA2R titres may help to identify those likely to achieve spontaneous remission and enable physicians to avoid immunosuppression. Antibody titres may also be important for prognostication at initial diagnosis.

• Hofstra et al found that patients with high antibody titre at time of diagnosis were less likely to achieve spontaneous remission. In a further study, the group determined that when patients were commenced on immunosuppressive treatment, the antibody titre falls rapidly, preceding the fall in proteinuria and concluded that the chance of achieving remission is higher if the initial anti-PLA2R antibody titre is low.
• Qin et al postulated that anti-PLA2R titre may have prognostic significance as there was a shorter time to clinical and biochemical remission in patients with low antibody titres. Levels at the end of treatment may also be beneficial in predicting long-term clinical outcomes.
• Bech et al found that almost 2/3 of patients with  undetectable anti-PLA2R antibodies at the end of treatment in clinical remission, while all who had detectable anti-PLA2R antibody after therapy experienced clinical relapse.

In the time since PLA2R was reported as the specific podocyte antigen in primary MN, testing has become a standard part of the diagnosis and workup of MN. Assessment of both circulating PLA2R autoantibody and PLA2R in biopsy samples will likely have significant prognostic and therapeutic implications. The discovery of a reliable indicator of primary MN is particularly relevant given the “rule of thirds” and variable disease course.

Post by Laura Slattery, NSMC Intern 2018

The use of Rituximab in Kidney Disease

Rituximab, the monoclonal chimeric anti-CD20 antibody, is an effective B-Cell depleting agent and continues to gather data for its use in a wide range of conditions relevant for the Nephrologist. It was also a pre-season favourite in the recent NephMadness event run by our friends at eAJKD, so I figured a quick recap was timely. As the literature is vast and grows by the week, I will only give a brief review of the current data, much of which is weak consisting of small observational reports.

Lupus Nephritis
The jury is still out. The LUNAR study randomized 144 patients with proliferative LN to Rituximab 1g x 4 or placebo with both groups receiving MMF & steroids. The experimental group had a decrease in anti-dsDNA and complement levels. Remission rates were numerically, but not statistically, better with add-on Rituximab (57% V 46%). While a lack of benefit with additional use of Rituximab was demonstrated, whether it could be an alternative to MMF is not known. In cases of resistant LN, we again have multiple favourable case series but no hard evidence.

Steroid-Resistant Nephrotic Syndrome (SRNS)
Evidence suggests Rituximab may be effective in steroid-dependent or calcineurin inhibitor-dependent patients, allowing withdrawal of one/both agents. An open-label RCT in 54 children with SRNS examined standard therapy (with steroids & calcineurin inhibitors) to Rituximab with lowering doses of usual therapy. The experimental arm had lower proteinuria, less relapse and was more likely to be drug free at 3 months. However, relapse did occur in 18.5% of Rituximab treated patients at the time of recovery of the B-Cell population.
The data does not all demonstrate a benefit however, which brings us to a recent small case series in the NEJM. Another anti-CD20 monoclonal antibody, this time the humanized preparation Ofatumumab, was reported to be an effective treatment in 5 cases of SRNS refractory to Rituximab. Although both are anti-CD20 antibodies, they have different epitope specificities which may explain the outcome in this small series. This reinforces the idea that B-Cell depletion is more complex than some may presume.

Minimal Change Disease
No RCT data exists but observational series suggest a benefit in steroid-dependent, but not resistant cases. A new case series in NDT reports on 16 adult patients with MCD who were steroid-dependent (n=12) or resistant and given 2-4 doses of Rituximab. Overall, 13 had a complete and 2 a partial remission with one non-responder. No serious adverse events were reported but 7 relapsed after 9–28 months.

Membranous Nephropathy (MN)
Guess what? No RCT data exists but limited data suggests it may be a useful agent. (See Nate’s previous post). The largest observational study I could find included 100 patients, 32 of whom had disease resistant to other immunosuppressive agents. Baseline proteinuria of 9g/day had been present for a mean of 2 years. Complete/partial/no remission was achieved in 27/38/35 patients respectively, remissions after a mean of 7 months. Prior immunosuppressant use did not appear to alter outcome. Other smaller studies also report that patients, including those with resistant disease, may respond.
There is evidence that Rituximab may cause a decrease in Anti-M-type Phospholipase A2 Receptor (PLA2R) antibodies. In this study, 25/35 patients with idiopathic MN had Anti-PLA2R antibodies, and these autoantibodies declined or disappeared in 17 (68%) of these patients within 1 year of rituximab treatment. The patients who demonstrated antibody response had much improved rates of complete and partial remission in this small study. Perhaps these autoantibodies may prove to be a useful biomarker for treatment response in MN.

ANCA associated vasculitis (AAV)
As per the RAVE study (& RITUXIVAS), there is now robust evidence that a 4 week course of rituximab is non-inferior to cyclophosphamide in the treatment of AAV, including a finding that it may be superior to conventional immunosuppression in relapsing patients. Note that only 2/3 of patients had renal impairment in RAVE with creatinine clearances of 54-69mls/min in the 2 groups. See my previous post for more detail.

FSGS
Limited evidence suggests it may be beneficial in steroid-dependent but not steroid-resistant cases. We must be wary of publication bias from early series which reported  positive findings, especially as they have often failed to be replicated. It has been used with some success for recurrent FSGS post-transplantation, often together with plasma exchange. There is growing evidence for a direct effect on the podocyte, as well as its known anti-B Cell effect, possibly via binding of podocyte proteins such as SMPDL-3b.

Transplantation
It is beyond the scope of this post to delve into the use of Rituximab in transplantation. It can be used in desensitization protocols, PTLD and treatment of acute antibody-mediated rejection (AMR) as adjuncts to IVIG and plasma exchange (trial data awaited regarding allograft outcome). There is no clear evidence for its use in chronic AMR, which tends to have little response to any agent.

Another indication is essential mixed cryoglobulinemia. Here, Rituximab has been reported to be beneficial in cases usually associated with Hepatitis C infection. See Gearoid’s previous post.
Overall, B-Cell depletion in general is an exciting treatment strategy for many of the disease processes we deal with. Like much in Nephrology, we lack strong data for if, when and how to use it. We also lack thorough knowledge as to its precise mechanism of action. Suggestions of a direct podocyte effect in glomerular disease and different mechanistic effects of alternate anti-CD20 preparations illustrate how much we have to learn.

Update on Membranous Nephropathy

U Penn established an annual one-day seminar in nephrology symposium. This year was titled “New Horizons in Nephrology: Updates in Glomerular Disease”.

Dr. Beck from Boston University gave the update on membranous nephropathy (MN). Previously, we discussed his article in the NEJM in detail, and today we will go over some key points and updates:

• 75% of MN is considered primary (idiopathic).
• IgG4 subclass is predominant in idiopathic MN.
• Anti-PLA2R is highly specific for primary MN
• Co-localization of PLA2R and IgG4 within immune deposits on biopsy.
• The majority of patients with primary MN have circulating autoantibodies against PLA2R.

There is a clear association of anti-PLA2R with disease activity.

- Positive in nephrotic state.

- Declines prior to the decrease in proteinuria.

- Absent in remission.

- Returns with (or prior to) relapse.

- Associated with recurrent MN

Methods of testing:

- Western blot

- Indirect immunofluorescence test

- ELISA : Will likely be the test of choice. Available in Europe, not yet in the US.

Treatment:

- Do NOT use corticosteroid monotherapy or MMF monotherapy for initial therapy of MN.

- No single definitive immunosuppression could be easily identified.

Current Initial therapy :

• Ponticelli regimen: methylprednisolone 1g/d iv x 3 doses followed by oral prednisone 0.5mg/kg/d in months 1,3,5; oral cyclophosphamide (2mg/kg/d) in months 2,4,6.
• Alternative initial therapy for those who refuse or have contraindications to cyclophosphamide is Calcineurin inhibitor (CNI) for at least 6 months.
• Stop if no remission in 6 months.
• If remission is attained, reduce dose every 1-2 mo by 50% and continue for at least 12 months 

Posted by Tarek Alhamad

Does nephrology need personalized medicine?

Systems biology is one of science’s growth areas. Sequencing technologies and software tools developed on the back of the human genome project have reduced the cost of, and therefore increased access to, large and complex datasets (ending in -ome) of genome sequences (genomics), gene expression (transcriptomics) and proteins and metabolites (proteomics and metabolomics). Systems biological techniques integrate these datasets and provide insights into how phenotypes may emerge from interacting biological processes rather than isolated genes or proteins.

A recent editorial in the journal Nephrology Dialysis Transplantation examined this field in general and its relevance to nephrology. The authors mention that –omic datasets have been useful in modeling “self-organized highly interconnected networks”, and that such networks have implicated unexpected candidates in disease pathogenesis (see for example, this paper on cardiac hypertrophy). 

The review goes on to suggest that using the tools of systems biology to finely phenotype individuals will usher in an era of truly personalized medicine. However, it is not clear to me that a definite sequel to this type of analysis will be the personalization of treatment or even that the concept of personalized medicine is particularly suited to our current view of what constitutes clinical evidence.

Diseases such as the ANCA-associated vasculitides (AAV) are now known to exhibit genomic variability. Randomised controlled trials (RCTs) in AAV (such as here and here) have been hampered by: 

1. Short follow-up times 
2. Inter-group heterogeneity which may have affected outcomes. These factors have contributed to ongoing debate about the applicability of the results of these trials (see correspondence here). 
3. Additionally a recent trial in membranous nephropathy, likely to represent another disease with distinct –omic subsets, was marked by slow recruitment. 

 

All these points together suggest that it may be difficult to conduct meaningful clinical studies of distinct –omic subtypes in nephrological diseases. Currently, primacy is given to RCTs when evaluating the efficacy of new treatments; and in nephrology the community is finally beginning to produce the RCTs which have been absent historically. 

If the focus is to switch away from RCTs with their large, well-matched study groups and towards splitting groups up by some -omic fingerprint I am able to envisage a time when one has to choose between giving more credence to the results of larger, “non-personalised” trials or smaller studies featuring –omic data but lacking the controlled element of RCTs.  Would this represent progress?

Image of the Month

A man in his early 60s was being treated for metastatic adenocarcinoma of the lung for 2 years. Recently, he had  been complaining of increasing hemoptysis and a PET CT was performed which showed progression of his disease. He presented to the ED with general malaise, edema and abdominal bloating. His creatinine had increased from a baseline of 1.0 to 1.5mg/dl and he had >10g urinary protein daily. A renal biopsy was performed. Light microscopy revealed thickened basement membranes with some double-contour formation but no definite "spikes" Immunofluorescence showed dense granular staining for IgG along the capillary loops with some minor staining in the mesangium. The diagnosis was early secondary membranous glomerulopathy most likely related to the progression of his malignancy. An EM image is shown below (Click to enlarge)

Subepithelial deposits typical of membranous nephropathy are easily seen in the image (A). The overlying podocytes are damaged and the foot processes are effaced. The lower part of the image (B) shows an area at the junction of the capillary loop and the mesangium. Here, a deposit is also present but it appears that the overlying glomerular epithelium degenerated and is sloughing into the lumen. This is likely due to complement activation and the formation of membrane attack complexes induced by the presence of the deposits and is thought to be the cause of the severe proteinuria seen in this patient. It is important to note that this is not associated with inflammation because the complexes are out of the reach of inflammatory cells which is not the case where subendothelial deposits predominate. This case was not entirely typical because there were occasional subendothelial deposits noted throughout the glomerulus although they were few and their significance was uncertain. 


Thanks to Dr Bijol for the Image

Getting to the heart of the matter: Anti-PLA2R and MN

A 53-year-old Caucasian male presented with pulmonary embolism, and was found to have nephrotic syndrome. A kidney biopsy showed membranous nephropathy (MN). The disease progressed despite treatment and six years later, the patient underwent a pre-emptive living unrelated renal transplant with basiliximab induction and triple maintenance(prednisone, MMF and tacrolimus). Urine protein/creatinine ratio (U Pr/Cr) was about 1 g/g at the time of discharge. His serum creatinine (SCr) nadir at around 2 mg/dl, so a kidney biopsy was done at 1 month post-tx, showing no rejection and negative deposits on EM.

After 2 years of stable renal function and no significant proteinuria, he developed a rise in both SCr up to 3 mg/dl and U Pr/Cr up to 7 g/g. A biopsy showed recurrent membranous GN, with IF positive for granular staining with IgG1 and IgG4, and EM showing subepithelial deposits.

The two main differential diagnoses for new-onset proteinuria and renal allograft dysfunction are recurrent primary glomerulonephritis and transplant glomerulopathy (a form of chronic allograft injury which is generally believed to be immune-mediated). Idiopathic MN recurs in 30-40% of patients, usually between the 2nd and 3rd year. The outcome, as in the native kidney, can be variable, although spontaneous remission appears less common. It is tempting to speculate that transplantation selects a subtype of patients with severe disease (those who progressed to ESRD) and, therefore, patients with recurrent MN are more likely to progress than not. A study of protocol biopsies from the Mayo clinic suggested that histologic lesions of post-transplant MN persist and progress, and usually (in 86% or 12 of 14 patients) lead to clinical manifestations. The impact of recurrent MN on long-term graft survival remains unclear, and most data suggest no adverse effect, although a graft loss of 10% at ~4 years was reported in one study.

One of the exciting developments in our understanding of MN has been the identification of the antibody to M-type phospholipase A2 receptor (PLA2R), a podocyte antigen, in ~70% of patients with idiopathic MN. As has been noted previously in this blog, there is evidence suggesting that levels of the anti-PLA2R may correlate with both disease activity and the likelihood of clinical response to treatment with rituximab, a monocolonal Ab to CD20 that targets B cells. Treatment with rituximab has been shown to reduce foot process effacement and lead to regression of immune deposits in those who respond.

Stahl, et al reported a case of early recurrent MN in which anti-PLA2R Ab was detected pre-transplant and at the time of recurrence. Levels of the Ab fell rapidly (within 2 weeks) after treatment with rituximab, although proteinuria appeared to increase transiently (at 2 weeks), and then remit (at 2 months). It has been demonstrated in several reports that proteinuria is reduced gradually and may take several months to reach its nadir. Similarly, in our patient, we found (thanks to Dr. Becker's lab) that anti-PLA2R, as detected by Western blot, was present in sera pre-transplant as well as time of recurrence, and disappeared completely after treatment with 2 doses of rituximab (1 g each). Both SCr (2 mg/dl) and U Pr/Cr (1 g/g) had improved by 3 months (figure above).

Some interesting questions remain unknown: 1) Are patients with MN who have detectable antibody (at the time of transplantation or later) more likely to recur? 2) How long does the response to rituximab last? (Up to 2-year data have been reported by the Mayo group) 3) Would pre-emptive treatment with rituximab of patients who have detectable antibody (at the time of transplant or later) prevent clinical recurrence, and is it worth the risk? Sindhu Chandran, MD

Cyclosporine in Membranous Nephropathy: A non-immune modulatory effect to maintain remission?

This is the story of a 64 year old male mason with past medical history notable for hypertension and hyperlipidemia who was referred to me for evaluation of proteinuria.

The patient noted onset of lower extremity edema nine months prior to the clinic visit. At the time, he was admitted to the hospital due to increasing complaints of lower extremity edema and shortness of breath, and received the presumptive diagnosis of congestive heart failure. He had an echocardiogram showing preserved ejection fraction and no valvular abnormalities. A chest CTA was negative for pulmonary embolism and imaging of the lower extremities was negative for deep venous thromboses. His serum albumin at the time was 2.5 g/dl down from his baseline of 4.0 g/dl a few months prior. No urinalysis data was available from that admission. He was treated with furosemide to which he responded with resolution of his shortness of breath, but with no effect on his notable 3+ pitting edema. He was discharged from the hospital with cardiology follow up as an outpatient.

Teaching point: not all edema is heart failure! A simple urinalysis would have been revealing.

Now back to the case...

During this time period, the patient’s lower extremity edema and exertional dyspnea had not improved in spite of escalating doses of furosemide. He was admitted to the hospital again two months prior to the renal clinic visit, this time for hypertensive emergency treated with intravenous labetalol followed by escalation in his anti-hypertensive regimen which included beta blocker, calcium channel blocker and a small amount of ACE inhibitor. A urinalysis sent at this time showed 3+ protein. He was also subsequently noted to have a serum albumin of 1.3 g/dl. Of note, his renal function was normal at his baseline of 1.0 mg/dl on presentation to renal clinic. Quantification of his proteinuria revealed 13 gms/day.

The patient denied a family history of kidney disease or any known past episodes of kidney problems. He denied fever, headache, chest pain, visual problems, rashes, joint pain, muscle pain, abdominal pain, nausea, vomiting, dysuria, hematuria, or hemoptysis. He had noticed foamy urine over the past few months. He also complained of occasional dyspnea on exertion, which was markedly different from his baseline a year prior. Renal ultrasound was notable for kidneys measuring 14 cm bilaterally with no hydronephrosis and no masses. Ultrasound evaluation of the renal arteries revealed no renal artery stenosis.

He underwent a renal biopsy which revealed membranous glomerulonephritis.

The patient was initially managed with angiotensin converting enzyme inhibitor, angiotensin receptor blocker and diuretics. After a six month period -- fifteen months since the onset of symptoms -- during which there was no sign of spontaneous remission, we initiated treatment with Cyclophosphamide and high dose Prednisone.

The patient developed severe leukopenia, so Cyclophosphamide was discontinued. While we have some experience with Rituximab at our institution, this patient had normal renal function and therefore appeared to be a good candidate for a trial of Cyclosporine. We therefore initiated treatment with Cyclosporine at a dose of 3 mg/kg/day.

He responded well with reduction of his proteinuria to less than 2 gms/day. However, due to an episode of VZV/shingles, the Cyclosporine dose had to be decreased to 1 mg/kg/day, which resulted in trough levels less than 40 ng/ml. In spite of Cyclosporine levels well below these known to have a significant immunomodulatory effect, the patient achieved a surprising partial remission. It is of course conceivable that his remission was spontaneous, but this is not supported by the fact that he had been persistently nephrotic for 1.5 years prior to initiation of Cyclosporine treatment. Furthermore, the fact that the patient continues to be in remission 3 years later suggests that Cyclosporine may continue to exert a beneficial effect.

It is not surprising that Cyclosporine can be successfully used to achieve remission in patients with IMN. However, past experience has shown that many patients with IMN have recurrence of proteinuria once Cyclosporine is removed. On the other hand, the chronic use of Cyclosporine is known to result in a decline of renal function, and nephrologists have been reluctant to use it for a prolonged period of time in the nontransplant setting. It would therefore seem advantageous to devise therapeutic strategies for the use of low dose Cyclosporine to prevent recurrence of nephrosis.

Intriguingly, a 2008 study by the Mundel group suggests that Cyclosporine may have a new target: the glomerular podocyte. The authors present data in mouse models of acquired proteinuria, and specifically in mice that have been genetically modified to express calcineurin in a constitutive fashion. Interestingly, these mice develop severe albuminuria. Through a series of experiments, the authors subsequently determine that Cyclosporine confers an anti-proteinuric benefit through its protective effect on a critical, podocyte-specific molecule called synaptopodin. The preservation of synaptopodin ensures that the podocyte cytoskeleton remains intact, preventing the disruption of the glomerular filtration barrier.

These findings challenge our understanding of Cyclosporine as an immune modulatory agent for proteinuric kidney disease, and our long held belief that Cyclosporine puts patients in remission through its effects on T-cell activity. These data necessitate a closer look at the effects of traditional “immune modulatory” agents on the podocyte cytoskeleton.

Extrapolating from these data, is it possible to maintain podocyte health – and keep nephrotic patients in remission – by using Cyclosporine, or preferably targeted agents with similar podocyte-specific effects?

My patient enjoys a partial remission (currently proteinuria is less than 0.8 gm/day) on what would be considered "subtherapeutic" levels of Cyclosporine. However, if we begin to think of Cyclosporine as a podocyte-modulating agent, perhaps we also need to redefine what levels are “therapeutic.” This case suggests that lower doses may allow us to use Cyclosporine to maintain patients in remission with less concern for its nephrotoxicity. We have now employed this approach in a few other patients with IMN, with encouraging results thus far. Moreover, the use of low dose Prograf in some of our patients with FSGS has also proven to be effective in maintaining remission. Future clinical studies on these questions will be revealing. In the meantime, we are hard at work in the lab to identify new podocyte-specific anti-proteinuric agents.

Potential Use of Rituxan in Membranous Nephropathy

Take-home points from Mayo Clinic's Fernando Fervenza's excellent Renal Grand Rounds this morning, in which he addresses the potential use of rituximab as a treatment for membranous nephropathy:

-the "rule of thirds" that we learn about membranous nephropathy (e.g., 1/3 of patients will spontaneously remit, 1/3 of patients will stay the same, and 1/3 of patients will progress to ESRD) is not entirely accurate in that patients with an extremely high degree of proteinuria (e.g., more than 8-10 grams per day) have a very high rate of progression of kidney disease.  This becomes critical in interpreting the results of clinical trials; you really have to look at the baseline proteinuria characteristics of the cohort.

-in non-randomized controlled trials, investigators are finding that dosing Rituxan either using a 1gm iv at D+1 and D+15 protocol OR using a 375 mg/m2 every 4 weeks for 4 doses total leads to at least a partial remission in between 60-75% of membranous nephropathy patients, a rate which is seemingly greater than one would expect for spontaneous remissions. One such paper by Fervenza et al is shown here.  

-a randomized, controlled trial comparing Rituxan to another therapy (e.g., Cytoxan-prednisone or a calcineurin inhibitor) would really be necessary to fully recommend using this strategy in the treatment of membranous nephropathy.  However, it is not clear where the money for performing such a trial would or should come from--industry or government.  

-it may be necessary to look at longer end-points to fully assess the effectiveness of Rituxan.  Since Rituxan targets pre-B cells but not plasma cells, you presumably have to wait until the plasma cells die off for it to have full effect.  Furthermore, monitoring proteinuria (the current standard for evaluating clinical response) is not perfect since it may reflect chronic podocyte damage (which may take months to years to fully heal, if it ever does) rather than immunologically-mediated proteinuria.  

-it looks as if levels of the antibodies against the phospholipase A2 receptor which explains a good chunk of patients with membranous nephropathy correlates generally well with patients who respond to Rituxan; that is, patients who successfully achieve a remission with Rituxan tend to show a complete disappearance of this antibody as assessed by Western blog.  Although this does not prove causality, it does point to a potential means of monitoring patients for a potential response.  

Secondary Causes of Membranous Nephropathy

Although the majority of membranous nephropathy falls under the "idiopathic" category, there are a variety of causes of secondary membranous nephropathy. It is quite important to eliminate these entities as possible diagnoses, as the treatment for secondary membranous nephropathy relies primarily on treatment of the underlying cause of disease whereas idiopathic membranous nephropathy often involves the use of steroids and/or cytotoxic agents.

Broadly speaking, the secondary causes of membranous nephropathy can be broken down into 4 general categories:

1. Infection-associated Membranous Nephropathy: hepatitis B and hepatitis C are both associated with membranous nephropathy. Because diseases such as malaria, schistosomiasis, TB, and leprosy are likewise associated with membranous nephropathy, secondary nephrotic syndrome is likely much more common in developing countries subject to these tropical diseases. Syphilis is also on the list.

2. Disease-associated Membranous Nephropathy: it is well-known that MN may be see in lupus ("WHO Type V Lupus Nephritis") either alone or in combination with other lupus-related pathologies. A variety of the other conditions associated with MN are also autoimmune diseases (e.g., rheumatoid arthritis, Sjogren's syndrome). Diabetes mellitus and membranous nephropathy have also been linked, as has sickle cell disease.

3. Drug-induced Membranous Nephropathy: the classic offenders are gold, penicillamine, NSAIDs, and captopril, though there are case reports for many others.

4. Malignancy-associated Membranous Nephropathy: although there appears to be a increased relative risk of solid tumors and lymphomas in patients with membranous nephropathy as compared to the general population, this association is still somewhat poorly defined and remains controversial. Many would simply recommend age-appropriate cancer screening (e.g., mammogram, screening colonoscopy, etc) in the patient with newly-diagnosed nephrotic syndrome without any other evidence for malignancy rather than a large-scale imaging workup.

Rule of Thirds in Membranous Nephropathy

Keeping with our recent theme of "numerical rules in Nephrology", let's briefly discuss the "Rule of Thirds" for Membranous Nephropathy.

The "Rule of Thirds" is frequently taught in medical school and a useful way of thinking about the prognosis of membranous nephropathy. It states that roughly speaking, all patients with the diagnosis of membranous nephropathy can be broken down into 3 equally populated groups with different prognoses:

One third of the patients will experience a spontaneous remission (this particular group, while certainly a desired outcome for all patients, has made interpretation of clinical trials in membranous nephropathy somewhat difficult--you don't know if a particular test subject has gotten better because of a treatment, or would have done so on their own).

One third of the patients will have persistent proteinuria and a reduced but stable renal function.

One third of the patients will have progressive loss of GFR, often leading to ESRD. According to this source, the overall incidence of ESRD is 14% at 5 years, 35% at 10 years, and 41% at 15 years.

While useful for a global understanding of membranous nephropathy, however, the Rule of Thirds is a little too simplistic--we can more accurately predict a patient's prognosis based on risk-stratification. In this 2005 JASN review by Cattan, the author presents a well-utilized strategy for the decision of how aggressively to treat patients with membranous nephropathy. Generally, it advises breaking patients up into low-risk, medium-risk, and high-risk groups based on their response to conservative therapy (e.g., ACE-I/ARBs, edema and lipid management, blood pressure control, etc) over a 6-month period.

Those in the low-risk group (normal renal function and less than 4 grams/day proteinuria over a 6-month period) have less than a 5% risk for progression over a 5-year period and therefore should not be given aggressive immunotherapy.

Those in the medium-risk group (normal renal function and persistent proteinuria between 4 and 8 grams/day proteinuria over a 6-month period). This group has a much higher risk of poor outcomes without treatment than the standard "Rule of Thirds" would suggest, and therefore the data would suggest treatment such as cycling of cytotoxic drugs and steroids.

Those in the high-risk group (worsening renal function and proteinuria greater than 8 grams/day over a 6-month period) represented only about 10% of all patients with idiopathic membranous nephropathy, but make up a very high percentage of those who eventually go on to ESRD. These patients should receive aggressive therapy with the possibility of newer protocols (Rituxan, cyclosporine for failure to achieve remission, enrollment in new trials) and be advised that dialysis is a very real eventual possibility.

Exciting NEJM Membranous Nephropathy Article

A landmark paper on membranous nephropathy was published by Beck et al in the most recent issue of NEJM. Ultimately we will have to see if the finding is reproducible, but based on the data presented this represents a major breakthrough in understanding the pathogenesis of membranous nephropathy and nephrotic syndrome.

There has long been strong evidence in support of a circulating factor which causes podocyte injury and resultant nephrotic syndrome. Additional evidence from the neutral endopeptidase story further suggested that an autoantibody directed again some podocyte antigen might be the culprit. In this issue, the researchers demonstrate that in 70% of patients with idiopathic membranous nephropathy (but 0% of patients with secondary membranous nephropathy or other forms of proteinuric kidney disease such as FSGS or diabetic nephropathy) contain an autoantibody against the podocyte antigen phospholipase A2 receptor. Furthermore, the autoantibody's presence appears to correlate with disease activity, suggesting a possible pathogenic role.

The work has a number of implications. First, it suggests that membranous nephropathy is indeed a separate disease than FSGS and other distinct forms of nephrotic syndrome. The common final pathway for proteinuria is the same (podocyte injury), but the ways in which to get there is likely different. Second, it suggests that detection of serum antibodies against phospholipase A2 receptor may be a useful part of the diagnostic workup for nephrotic syndrome--perhaps even making biopsies unnecessary--and perhaps could be used to follow disease activity in response to various therapeutic maneuvers. That is, this test may well become the "ANCA" of membranous nephropathy.