Successful Treatment of a 42-Year-Old Man with Concurrent Anti-Glomerular Basement Membrane Disease and Anti-Phospholipase A2 Receptor Antibody-Positive Membranous Nephropathy: A Case Report

Introduction

Anti-glomerular basement membrane (anti-GBM) disease is a rare small-vessel vasculitis. It is caused by autoantibodies targeting the non-collagenous domain 1 (NC1) of a3 chain of type IV collagen (a3 [IV]) expressed in glomerular and pulmonary capillaries [1]. It typically presents as rapidly progressive glomerulonephritis that results in kidney failure, with or without involvement of pulmonary alveolar hemorrhage [1]. The incidence of anti-GBM disease is reported to be 0.6–1.64 per million population in different demographic regions [2,3]. Moreover, the disease is known for its poor patient and kidney outcomes if not diagnosed early and treated promptly. The 1-year patient and kidney survival rates were reported to be approximately 70% and 40%, respectively, in China [4].

Clinical diagnosis of anti-GBM disease mainly depends on the detection of elevated serum anti-GBM antibody titers and progressively increasing serum creatinine level. Typical kidney histology changes include linear IgG deposition along the GBM and, in most cases, crescent formation in the glomeruli [1]. Standard treatment for anti-GBM disease includes plasmapheresis to rapidly remove pathogenic autoantibodies, together with cyclophosphamide and corticosteroids to inhibit further autoantibody production, thereby ameliorating end-organ damage [5]. Anti-GBM disease can occasionally occur in conjunction with a second disease. Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is the most common concurrent disease, which occurs in up to 40% of patients with anti-GBM disease [6].

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Recent studies have revealed that primary MN is mediated by antibodies targeting either the M-type phospholipase A2 receptor (anti-PLA2R) in approximately 85% of cases, thrombospondin type-1 domain containing 7A (THSD7A) in 3–5% of cases, and through other unidentified mechanisms in the remaining 10% of cases [7]. The kidney histology is characterized as subepithelial immune deposit of IgG and complement along the glomerular capillary wall and typically does not present with crescents. Patients with primary MN and proteinuria are recommended to receive optimal supportive care. Immunosuppressive therapy is reserved for patients at moderate or high risk of progressive kidney disease [5].

The combination of anti-GBM disease and MN is rare. Only a few cases have been documented so far, with very poor kidney outcomes [8,9]. Herein, we report successful treatment of a 42-year-old man who presented with acute kidney injury who had been diagnosed with combined anti-PLA2R antibody-positive membranous nephropathy and anti-GBM disease.

Case Report

A 42-year-old male Chinese patient without remarkable medical history visited a kidney clinic in October 2022, with chief concerns of edema, foamy urine, and fatigue for 3 days. He also reported coughing and white phlegm, which started 2 weeks ago. An inquiry on family medical history revealed that his daughter was diagnosed with nephrotic syndrome several years ago, with complete remission after treatment (kidney pathology unknown).

Physical examination showed normal body temperature, blood pressure of 119/76 mmHg, and severe edema of both lower extremities. Blood tests revealed high serum creatinine of 2.82 mg/dl (eGFR 26.39 ml/min/1.73 m2, CKD-EPI), low serum albumin of 24.4 g/l, and high serum C-reactive protein (CRP) of 186 mg/dl. Urinalysis revealed trace proteinuria and high red blood cell (RBC) count (>100/HP) and white blood cell (WBC) count (10–15/HP) in the sediment. The patient was admitted to hospital on the same day for further examination.

On day 2 of hospitalization, his serum creatinine concentration was increased to 3.74 mg/dl (eGFR 18.86 ml/min/1.73 m2, CKD-EPI), and urine output was approximately 1000 ml per day, which was slightly decreased after admission. The random urinary albumin-to-creatinine ratio (ACR) was 679.22 mg/g and 24-hour urinary total protein (UTP) was 2.69 g. Abdominal ultrasound revealed normal kidney size and morphology bilaterally. Serological tests showed a high anti-GBM antibody concentration of >500 AU/ml (normal <20 AU/ml, ChemiLuminescence), which revealed the diagnosis of anti-GBM disease. Serum WBC count was 11.84×1012/l, CRP was 144.7 mg/dl, and procalcitonin (PCT) was 0.447 ng/ml. Serum anti-myeloperoxidase antibodies (pANCA) and anti-proteinase 3 antibodies (cANCA) were negative. Chest computed tomography (CT) demonstrated no obvious pulmonary exudation.

Methylprednisolone (MP) was immediately administered intravenously (40 mg daily for days 2–5, 240 mg daily for days 6–10, 80 mg daily for days 11–16, and 40 mg daily starting on day 17). Since the patient presented upper-respiratory tract infection symptoms and serum CRP concentration was elevated, corticosteroid was initiated at a low dose and gradually increased under close supervision to avoid risk of infection. Prophylactic antibacterial treatment of levofloxacin was given intravenously at 0.25 g/day from days 1 to 14. Intravenous injection of immunoglobin was given at 20 g/day from days 2–6. Starting from day 3, double-filtration plasmapheresis (DFPP) was conducted 3 times a week over the course of 3 weeks (KM-9000, Sanyo, Japan). Plasma was separated from blood cells using a first filter (Plasmaflo OP-08W). A second filter (Cascadeflo EC-20W) was then used to eliminate the anti-GBM antibodies. On day 20, serum anti-GBM antibody titer was reduced to 66.4 AU/ml and DFPP was stopped due to high costs. In addition, 0.2 g of cyclophosphamide was given intravenously on days 10, 16, and 20 after procedures of DFPP. An additional dose of 0.4 g cyclophosphamide was given on day 23. Treatments during the hospitalization are summarized in Figure 1.

A kidney biopsy was performed on day 24 after discontinuation of plasmapheresis. Under light microscopy, 10 glomeruli were examined, 2 of which showed global sclerosis (Figure 2A, 2B). A mixture of cellular or fibro-cellular crescents were seen in Bowman’s capsule of 4 glomeruli, with 1 large crescent and 3 small crescents. Two glomeruli showed ruptured Bowman’s capsule wall, 2 glomeruli showed segmental fibrinoid necrosis, and 2 glomeruli showed segmental adhesion sclerosis. All glomeruli demonstrated stiff capillary loops and were irregularly thickened. Periodic Schiff-methenamine silver (PASM) staining indicated vacuole-like changes under the epithelium, moderate-to-severe tubulointerstitial lesions, focal detachment of the brush border of tubular epithelial cells, cells flattened, lumen dilation, focal atrophy and degeneration, protein cast, focal interstitial inflammation and fibrosis, and arteriolar intimal thickening and stiffness. Electron microscopy showed electron-dense immune complex-type deposits in the subepithelial layer and inside the GBM, with GBM reaction (Figure 2C). Moreover, extensive diffusion of the epithelial cell feet was seen. Immunofluorescence IgG staining showed 3+ positivity of both linear and granular deposit along the capillary loop (Figure 2D). Further staining for IgG subclasses demonstrated linear and granular deposit of IgG1 and granular deposit of IgG4, with slightly higher expression of IgG1. In addition, immunofluorescent staining demonstrated positivity of 3+ intensity for anti-PLA2R antibody (Figure 2E), using rabbit anti-human anti-PLA2R1 antibody (dilution ratio 1: 200, Atlas Antibodies) and goat anti-rabbit secondary antibody (dilution ratio 1: 100, Jackson Immuno Research). Based on the histology characteristics of kidney biopsy, anti-GBM disease concurrent with MN was diagnosed, together with acute kidney tubular injury and arteriolar stiffness.

Serum anti-PLA2R antibody and anti-THSD7A antibody concentrations were tested on day 29, and both were within normal range. Serum anti-PLA2R antibody level was measured by enzyme-linked immunosorbent assay (ELISA, Euroimmun).

Over the course of hospitalization, the patient’s serum anti-GBM antibody level declined gradually, accompanied with constant reduction of serum creatinine (Figure 1). Serum anti-GBM antibody concentration was 73.1 AU/ml and creatinine level was reduced to 2.5 mg/dl on day 29, with serum CRP of 1.4 mg/dl and albumin of 24 g/l. An additional 0.6 g of cyclophosphamide was given on day 30. The patient was discharged on day 31 and intravenous MP was changed to oral prednisone 40 mg daily.

The patient came back to the clinic for a follow-up 14 days later. Laboratory results revealed serum creatinine of 1.85 mg/dl, albumin of 25.4 g/l, and anti-GBM antibody of 47.3 AU/ml. Urinalysis revealed RBC count of 25–30/HP and 24-hour UTP of 2.8 g. An additional 0.8 g of cyclophosphamide was administered intravenously and oral corticosteroid was continued. The patient was subsequently followed up at a local hospital in his hometown. He received monthly injection of cyclophosphamide for a total of 6 months (accumulated dose of 5.6 g). Corticosteroid was tapered and maintained at a dose of 5 mg daily after 5 months. Recent laboratory results at the local hospital showed that the serum anti-GBM antibody was almost undetectable, serum creatinine was decreased to 1.27 mg/dl, and serum albumin rose to 37 g/l. Urinalysis revealed trace proteinuria and RBC count of 13–14/HP, and 24-hour UTP was reduced to 0.57g.

Discussion

Anti-GBM disease can occur in conjunction with a second disease, the most common being ANCA-associated vasculitis. Coincident anti-GBM disease and MN have been rarely reported. Herein, we present a case of a 42-year-old man with anti-GBM disease combined with PLA2R-positive MN. The kidney biopsy showed linear and granular deposit of IgG along the capillary loop, supporting the diagnosis of concurrent anti-GBM disease and MN. The patient demonstrated fully recovered kidney function and partial remission of MN after prompt treatment with glucocorticoid, plasmapheresis, and cyclophosphamide. Early diagnosis and effective treatment are essential points in achieving kidney function recovery and dialysis independence.

The pathogenesis of combined anti-GBM disease and MN is unclear. One hypothesis is that immune complex deposits formed in MN can cause damage to the basement membrane, leading to release of autoantigens from the basement membrane into the circulation, which in turn stimulates the production of anti-GBM antibodies. Indeed, Klassen and co-authors first described a case of anti-GBM glomerulonephritis with previous biopsy-proved MN in 1974 [10]. The patient died of acute kidney failure. Postmortem autopsy showed crescent nephritis superimposed on the membranous changes. IgG eluted from the patient’s kidney tissue was capable of binding to the GBM of normal human and monkey kidneys and inducing acute anti-GBM nephritis in monkeys. Since then, several other clinical cases where anti-GBM disease occurred following membranous glomerulonephritis have been reported [11–13]. Kurki and co-authors reported a patient who first developed membranous glomerulonephritis with nephrotic syndrome and 1 year later developed a crescentic, rapidly progressive glomerulonephritis with anti-GBM disease after presentation of an acute respiratory infection [12]. Interestingly, they retrospectively analyzed the patient’s serum samples collected during follow-up and found that anti-GBM antibodies started to increase in the serum obtained 2 months before the decline of kidney function. Similarly, our patient also presented declined kidney function following an episode of acute upper-respiratory infection. However, we were not sure whether he had asymptomatic membranous glomerulonephritis before the presentation of anti-GBM disease.

More recently, researchers found that the main antigen of anti-GBM disease, a3(IV)NC1, can lead to MN lesions in mice [14,15], which may partly explain the clinical findings that some patients developed membranous glomerulonephritis following anti-GBM disease [16–18]. Indeed, a case series study from China recruited 8 patients with combined anti-GBM disease and MN [19]. These patients demonstrated serum anti-GBM antibodies predominantly targeting α3 chain (a3(IV)NC1). On the other hand, in patients with classic anti-GBM disease, a broader spectrum of antibodies against all the 5 α chains were detected in the serum [19].

PLA2R has been identified as a major antigen for idiopathic MN [20]. Serum anti-PLA2R antibody was found to be negative in most patients with combined MN and anti-GBM disease, but glomerular anti-PLA2R antibody staining was occasionally positive [8,19]. Molnár et al recently reported a case of combined anti-GBM disease and MN in which anti-PLA2R antibody was positive both in the serum and in the kidney specimen [21]. In the current case, kidney histology demonstrated positive staining of PLA2R antibody and granular deposit of IgG4 along the capillary loop in addition to anti-GBM lesions. These characteristics collectively suggested idiopathic membranous nephritis concurrent with anti-GBM disease. However, we did not measure serum anti-PLA2R antibody level at disease onset; therefore, it is unclear whether the negative anti-PLA2R antibody detected on day 29 was related to DFPP therapy, which can eliminate the antibodies from circulation.

Patients with concurrent anti-GBM disease and MN demonstrated relatively lower levels of serum creatinine and better kidney outcomes compared to those without MN [19,22]. This may be explained by different clinical and immunological features, including younger age, male predominance, narrower antigen spectrum of anti-GBM antibodies, lower anti-EB antibodies, and lower circulating anti-a3(IV)NC1 IgG1 and IgG3 in patients with concurrent anti-GBM disease and MN [19]. Previous studies have reported that anti-GBM IgG1 and IgG3 may play a major role in the initiation and progression of anti-GBM disease [23]. In the present case, we did not measure the subclasses of serum anti-GBM antibodies, but glomerular immunofluorescence staining revealed linear IgG1 deposition and negative IgG3 staining, which may partly explain the good kidney outcome of our patient. Moreover, kidney outcomes seemed to be better in Asian patients based on the 3 case series published so far [8,19,22]. Indeed, Patel et al reported a case of a 59-year-old Hispanic man who presented with acute kidney injury [24]. Subsequent work-up, including a kidney biopsy, revealed anti-GBM disease with underlining membranous nephropathy. Different from our case, cellular crescents were demonstrated in all examined glomeruli. The patient remained dialysis-dependent despite receiving a treatment regimen similar to that provided in our case [24]. More recently, there was another case of a Hispanic male patient diagnosed with concurrent anti-GBM disease and PLA2R-associated membranous nephropathy [25]. The patient presented anuric. His kidney biopsy showed that 16 out of the 20 examined glomeruli contained circumferential cellular crescents associated with extensive fibrinoid necrosis and rupture of the GBM [25]. Although treated aggressively, the patient remained dialysis-dependent. Diffuse crescent formation in these 2 cases also contributed to the poor kidney outcome.

Early identification and prompt treatment are extremely important for kidney injury recovery, and treatment delay is a common reason for maintenance dialysis dependence [21,26]. In cases of highly suspected anti-GBM disease, treatments should start within 24 hours without waiting for confirmed diagnosis by kidney biopsy [5]. A combination of glucocorticoid, cyclophosphamide, and plasmapheresis is recommended for treatment of anti-GBM disease by the updated KDIGO guideline [5]. Steroid in combination with cyclophosphamide is also recommended as one of the first-line treatment regimens for membranous glomerulonephritis. In the current case, we followed the guideline by giving the patient prompt treatment using corticosteroid, DFPP, and cyclophosphamide. His serum creatinine level declined significantly after a short period of increase, accompanied with decreased circulating anti-GBM antibody titer. Therefore, dialysis was avoided with this effective and timely treatment. Rituximab, either used alone or in combination with corticosteroid and plasmapheresis, has been reported to be an alternative treatment for concurrent anti-GBM disease and MN [8]. Rituximab is a chimeric monoclonal anti-CD20 antibody that targets B cells and can exert therapeutic effects in anti-GBM disease by suppressing anti-GBM antibodies production by B cell depletion. Bandak et al reported successful use of rituximab to treat a case of refractory simultaneous anti-GBM disease and MN that failed to respond to conventional therapy [27].

Conclusion

We report a case of a 42-year-old man who developed acute kidney injury, with kidney biopsy findings of coexisting anti-GBM disease and PLA2R-positive MN. The patient showed fully recovered kidney function and reached partial remission of MN after treatment with corticosteroid, DFPP, and cyclophosphamide. Serological testing and kidney biopsies are critical for disease diagnosis. Prompt treatment is one of the key points for better kidney outcome.