Immune-complex-mediated membranoproliferative glomerulonephritis with linear IgG staining resembling atypical anti-glomerular basement membrane disease: a case report

Abstract

Anti-glomerular basement membrane (anti-GBM) disease typically presents as rapidly progressive glomerulonephritis, however an atypical anti-GBM nephritis with various light microscopic findings without crescentic formation has been reported in recent years. The findings reported including cases with membranoproliferative glomerulonephritis (MPGN) pattern. Few reports have been able to follow the course of the disease over a long period of time. We report a case of MPGN associated with the spectrum of atypical anti-GBM nephritis that showed a slowly progressive course over more than eight years. A 49-year-old man underwent kidney biopsy because of hypertension, proteinuria, and mild renal insufficiency. The findings on kidney biopsy showed the findings of MPGN. Immunofluorescence microscopy revealed bright linear staining of IgG on the GBM. Electron microscopy showed subepithelial, intra-basement membrane, subendothelial, and paramesangial electron-dense deposits. Serum anti-GBM antibodies were negative. Proteinuria had been present for 4 years prior to the renal biopsy, however no worsening of renal function was observed. Because of worsening proteinuria and the presence of endocapillary hypercellularity in the tissues, the intravenous and oral steroids were started. Although the proteinuria showed slight improvement, the serum creatinine level was stable around 1.5–1.7 mg/dl. Although some indolent cases of atypical anti-GBM syndrome were reported previously, compared with these cases, our patient had more stable renal function for a long time. This is a rare case of resembling atypical anti–GBM disease that shows MPGN with linear IgG staining having a long-term indolent course and without secondary etiology.

Introduction

Although glomerular basement membrane (GBM) nephritis typically present as crescentic nephritis, Nasr et al. reported atypical anti-GBM nephritis presenting linear GBM staining for immunoglobulins (Igs) but without a diffuse crescentic phenotype. In these patients, renal insufficiencies were mild, and they did not have pulmonary hemorrhage. A previous study reported an atypical anti-GBM disease with a progressive clinical course [1]. According to Nasr [2], atypical anti-GBM nephritis can have various pathological findings on light microscopy. We experienced a case of MPGN with bright linear GBM staining but without crescentic findings, and the course of the renal insufficiency was slow and sustained. Since those reports did not follow a long period of time, we report a case of atypical anti-GBM nephritis.

Case report

A 49-year-old Japanese man presented with proteinuria of 1.5 g/gCr. He also had hypertension for 10 years and dyslipidemia and hyperuricemia. His blood pressure at the first visit was 190/100 mmHg, and he had not consulted a doctor even if he was informed to have hypertension during a health checkup conducted a long time ago. Secondary hypertension was ruled out through careful examination, and his blood pressure had been well controlled to ~ 130 mmHg by antihypertensive drugs. His chief complaint was leg edema. Renal function decline was suggested based on his serum creatinine level of 1.44 mg/dL, which was maintained at the same level for 7 years. Diabetes mellitus was not suggested, and any autoimmune diseases and antineutrophil cytoplasmic antibody-associated vasculitis were denied following detailed assessment. Monoclonal Ig was negative on serum and urine immunoelectrophoresis. Results from multiple serum free light-chain studies showed normal levels of κ and λ light chains with κ:λ ratio of 1.23, and monoclonal disease with κ dominance was thought to be negative. Although renal biopsy was recommended, he did not agree with it, and he was taking antihypertensive drugs for 7 years. He had been prescribed four types of antihypertensive drugs (namely, candesartan cilexetil, an angiotensin II receptor blocker (ARB) 8 mg, doxazosin 2 mg, amlodipine besilate 5 mg, and torasemide 4 mg), statins, and anti-hyperuricemic drugs. The excretion of urinary total protein gradually increased in 6 months to 3 g/gCr; as a result, he agreed to the renal biopsy. With regard to family history, his father had hypertension without kidney disease. He did not have a history of smoking. On admission, he was afebrile, and his blood pressure was 134/86 mmHg. The patient was 167.9 cm tall and weighed 67.4 kg, corresponding to a body mass index (BMI) of 23.9 kg/m², and he was not obese, including before hospitalization. He had pitting edema on both legs. No signs of skin lesions were noted. His white blood cell (WBC) count was 5,600/μL and C-reactive protein level was slightly elevated (0.7 mg/dL). His total protein and albumin levels were 4.8 and 2.9 g/dL, respectively, and his serum creatinine level was 1.34 mg/dL. His glucose (fasting) level (87 mg/dL on admission) had not increased during the clinical course, and hemoglobin A1c was 5.6%. Ophthalmologic examination revealed no diabetic retinal findings. In addition, there were no changes in dietary habits or body weight during the clinical course. Therefore, the presence of diabetes mellitus was considered unlikely. His low-density lipoprotein cholesterol was 66 mg/dL.

Urinalysis revealed hematuria with 1–4 red blood cells/high-power field (HPF), < 1 WBC/HPF, 1 + fatty casts, and protein excretion of 3.23 g/gCr. In the 24 h urine test after the renal biopsy, when urinary protein was 0.84 g/day, urinary microalbumin was 0.622 g/day, indicating that the urinary protein was predominantly albumin. The N-acetyl-β-D-glucosaminidase level in the urine increased to 10.1 U/L. The immunoglobulin G (IgG) and IgG4 levels were 861 and 155 mg/dL, respectively, and complement activity was normal. Serological tests for antinuclear antibodies and anti-neutrophil cytoplasmic autoantibodies were negative. Anti-streptolysin O antibody was normal (75 IU/mL). Anti-GBM antibody was not high (< 2.0 U/mL). Hepatitis B surface antigen, anti-hepatitis C virus antibody, and anti-human immunodeficiency virus antibody were all negative. An abdominal ultrasonography revealed mild atrophy of both kidneys. These findings indicated proteinuria, renal insufficiency without remarkable inflammatory signs, and any increase in autoantibodies, including anti-GBM antibodies. Chest X-ray imaging revealed no finding on the lungs, such as consolidation and ground-glass opacities. We could not confirm the episode and the focus of infection.

The renal biopsy specimen contained nine glomeruli with two global scleroses. The glomeruli tended to be hypertrophic. Light microscopy revealed segmental endocapillary hypercellularity and increased mesangial matrix and mesangial hypercellularity with the double contour of the GBM (Fig. 1a, b). The tubulointerstitial area showed patchy tubular atrophy and interstitial fibrosis with mild-to-moderate infiltrations of inflammatory cells. Some of the tubules showed enlargement of the lumen and swelling of epithelial cells. Fibrous intimal thickening and hyalinization were seen in the arcuate artery and arteriole, respectively. Direct immunofluorescence study showed linear IgG staining on all GBMs (Fig. 1c) and granular C3 staining on the mesangial area (Fig. 1e). No immunoreactants were found in the tubulointerstital areas. IgG on the GBM included IgG1 and IgG4, with a dominance of IgG1 (Fig. 1d). Immunofluorescence staining for IgA, IgM, and C1q demonstrated weak positivity (± to 1 +) in a mesangial and peripheral granular pattern. Immunofluorescence for C4d showed linear staining on the GBMs (Fig. 1f) and mesangial area, and that for κ showed linear staining on the GBMs. Immunofluorescence for κ (Fig. 1g) showed linear staining along the GBMs, and immunofluorescence for λ (Fig. 1h) also demonstrated linear positivity on the GBMs; however, κ staining was stronger than λ staining. Electron microscopy showed subepithelial, intra-basement membrane, subendothelial, and paramesangial electron-dense deposits and subendothelial swelling (Fig. 1i) which did not match the linearly positive sites for IgG in immunofluorescence. No concordance was identified between complement deposition and electron microscopy-detected immune complex deposition. The finding of membranoproliferative glomerulonephritis was accompanied by findings of focal segmental glomerulosclerosis-like lesions.

Fig. 1.

Photomicrographs of the renal biopsy tissue. a, b Light microscopy shows segmental endocapillary hypercellularity and increased mesangial matrix and mesangial hypercellularity with double contour of the GBM. a PAS staining. b PAM staining. Original magnification, × 400. c The direct immunofluorescence study showed bright linear IgG staining on all GBMs. d On the GBM, IgG1 was the dominant IgG. e Immunofluorescence for C3c showed granular staining on the mesangial area. f Immunofluorescence for C4d showed linear staining on the GBMs and mesangial area. Electron microscopic findings. g Immunofluorescence for κ showed linear staining along the GBMs. h Immunofluorescence for λ also showed linear positivity along the GBMs. i Subepithelial, intra-basemembrane, subendothelial, and paramesangial electron dense deposits were presented. GBM, glomerular basement membrane. j Higher-magnification electron micrograph showing electron-dense immune complex deposits (arrow) within a partially exudative-appearing lesion and the subendothelial glomerular basement membrane. k Higher-magnification electron micrograph showing that linear IgG deposition along the glomerular basement membrane did not correspond to the electron-dense immune complex deposits

The nephritis-associated plasmin receptor (NAPlr) staining for searching the possibility of infection-related glomerulonephritis was negative [3, 4]. An indirect immunofluorescence study was performed to evaluate whether the patient’s serum contained IgG, which bound to the GBM. Renal frozen sections from normal tissues were incubated with the serum from the patient as follows: as positive control, a patient with an anti-GBM disease, or as negative control, a healthy individual, or the present patient. It was followed by fluorescein isothiocyanate-labeled anti-human IgG antibody. Although the positive control showed linear IgG staining on the GBM, the negative control and the present patient’s serum did not stain for glomeruli.

Renal biopsy showed findings of membranous proliferative glomerulonephritis with linear staining of IgG on the glomerular membrane, although we searched the factors of secondary MPGN. Two months after the renal biopsy, considering the presence of primary MPGN, intravenous administration of methylprednisolone (500 mg/day, 3 days) and oral administration of prednisolone (30 mg/day) were started and gradually tapered. The proteinuria showed slight improvement (was 3.0 g/dL, to 1.5–2.3 g/dL). The clinical course is shown in Fig. 2. At the time of referral to our hospital before the renal biopsy, the patient was already taking candesartan 4–8 mg as an ARB. Blood pressure was subsequently controlled with a calcium channel blocker, but there were no significant changes in urinary protein levels or serum creatinine. After steroid therapy, urinary protein decreased to approximately one-half to two-thirds of the previous level.

Fig. 2.

Time course before the renal biopsy and after the treatment. The bar graph demonstrates the change in urinary protein, and the polygonal line graph demonstrates the serum creatinine

Discussion

The renal biopsy demonstrated MPGN pattern, and immunofluorescence revealed linear IgG staining along the GBM. Although circulating anti-GBM antibodies were negative, the clinicopathologic features were considered to fall within the spectrum of atypical anti-GBM nephritis. Nasr et al. reported 20 patients with atypical anti-GBM nephritis characterized by bright linear immunoglobulin staining along the GBM without diffuse crescentic glomerulonephritis [2]. Histologic findings were heterogeneous, including an MPGN pattern in three patients, suggesting a broad clinicopathologic spectrum. In our case, both κ and λ staining were observed along the GBM, precluding definitive light-chain restriction. Nevertheless, linear IgG deposition along the GBM and the absence of circulating anti-GBM antibodies suggested overlap with atypical anti-GBM nephritis. Although the lesion most closely resembled the MPGN pattern described by Nasr et al., the presence of immune-complex deposits on electron microscopy favors immune complex-mediated MPGN with overlapping features of atypical anti-GBM nephritis rather than pure atypical anti-GBM disease. C3 deposition was not concordant between electron microscopy and immunofluorescence findings, suggesting that the condition was neither C3 glomerulopathy nor immune complex–mediated MPGN. Although the pattern was not entirely typical of immune complex–mediated glomerular injury, the patient had no history of diabetes mellitus or any other chronic condition known to cause secondary glomerular exudative lesions. Furthermore, the presence of immune complex deposits could not be disregarded. Our interpretation of immune complex-mediated glomerular injury was based on the overall pathological findings, particularly the coexistence of electron-dense deposits and an MPGN pattern, rather than the linear IgG staining itself. However, the exact composition of the electron-dense deposits remains uncertain, which is a limitation of the present report. Therefore, we considered that this case was best interpreted as immune complex–mediated membranoproliferative glomerulonephritis with overlapping features of atypical anti-GBM disease.

Although IgG stained linearly on the GBM, the serologic test results for anti-GBM antibody were negative in the 20 patients of Nasr [2]. Among typical anti-GBM nephritis cases, the four immunoassay-based anti-GBM antibody kits showed sensitivity of 94.7–100.0% and specificity of 90.9–100.0% for Goodpasture syndrome [5]. Despite the reported high sensitivity in the detection of serum anti-GBM antibodies, there is a possibility of false negative results. Several mechanisms have been proposed to explain this discrepancy between negative serologic findings and positive linear IgG staining along the GBM in atypical anti-GBM nephritis [6, 8]. First, the pathogenic antibodies may recognize non-classical GBM epitopes that are not detected by conventional anti-GBM antibody assays [6]. Second, the circulating antibody levels may remain below the detection threshold because of low antibody titers or rapid sequestration of antibodies within the glomerular basement membrane (the “immunological sink” phenomenon) [6, 8]. These mechanisms may explain why patients show linear IgG deposition on renal biopsy despite negative serum anti-GBM antibody testing. It has been suggested that extensive evaluation of atypical autoantibodies should be attempted, if possible, using improved assays and highly sensitive techniques [6] Some cases may or may not be positive by indirect immunofluorescence [2, 7], but our case was negative.

In our case, proteinuria was predominantly albuminuria, and the amount of urinary protein showed little change despite antiproteinuric therapy with an ARB and blood pressure control with a calcium channel blocker. The trajectory of renal function was indolent.

In the report by Nasr and colleagues, cases with a course over several years were not uncommon; however, we experienced an even more indolent clinical course. Specifically, In Nasr’s report, the follow-up duration was long, with 61 months as the longest course. The follow-up duration among patients with Cr level of < 1.3 mg/dL was up to 47 months. In our patient, the renal function based on the Cr level was stable for 84 months (7 years), and we could confirm its more indolent clinical course. Including both the pre- and post-treatment periods, the duration from transfer to our hospital to 3 months after completion of treatment was 8 years and 8 months. Of Nasr’s 20 patients with MPGN, three had the following clinical course: One patient presented with a focal crescent, received prednisone and cyclophosphamide, but died in 3 months because of pneumonia (last Cr level was 1.6 mg/dL). Another patient presented with diffuse endocapillary proliferative features and focal crescents, received methylprednisolone, prednisone, cyclophosphamide, and plasmapheresis, but developed end-stage renal disease 1 month after kidney biopsy. This case was post-renal transplantation. The other patient who had TMA findings received prednisone and mycophenolate mofetil, and its Cr level was 2.4 mg/dL, without hematuria. The proteinuria level of 1.5 g/day was sustained for 52 months. Based on these findings, in the report by Nasr and colleagues, patients with an indolent clinical course were not common; however, such cases were indeed present. In another report that studied five cases of atypical anti-GBM disease, the longest follow-up duration was 56 months (this was a post-renal transplantation case). Among these five cases, there was a case presenting hemoptysis or requiring hemodialysis [8]. Compared with these previous cases, our patient had stable renal function for the longest duration. During the 6-year period, renal function remained unchanged, but during one year there was an exacerbation of renal function. Although no clear factor is known, it is likely that the exacerbation was due to some influence, such as infection or drugs. Our case was treated due to worsening renal dysfunction. After steroid therapy, renal function remained largely unchanged, but urinary protein showed a decreasing trend. Although corticosteroid therapy was administered in the present case, renal function remained stable over the long term in some previously reported cases.

In Nasr’s patients, the smoking rate was 58%, and four patients had history of diabetes mellitus (DM). Our patient did not have secondary factors for MPGN including DM, secondary hypertension, and smoking [9–12]. Secondary causes of linear IgG staining, including infection-related glomerulonephritis, diabetic nephropathy, and monoclonal gammopathy, were excluded. The pathogenesis of atypical anti-GBM nephritis is currently unresolved, suggesting a heterogeneous pathogenesis. Secondary factors have been reported as possibly associated with lupus nephritis, Mycobacterium Avium, COVID19 vaccine, and methicillin-sensitive Staphylococcus aureus infection [13–16].

In conclusion, we describe a case with stable renal function over an extended period, suggestive of a milder or indolent variant that could lie within the spectrum of atypical anti-GBM nephritis. It is not clear whether slowly progressive atypical anti-GBM nephritis should be treated, and we hope that the accumulation of such cases will help define future treatment strategies.

Funding

No funding was obtained for this case report.

Declarations

Conflict of interest

The authors have declared that no Conflict of interest exists.

Informed consent

Informed consent In accordance with the guidelines of the Institutional Review Board of St. Marianna University Hospital, informed consent was obtained from the patient for publication of this case report, includ ing blood sampling and the presentation of her clinical course. Docu mentation of the consent is available in the electronic medical records of St. Marianna University Hospital.

Human rights

All procedures involving human participant were performed following the ethical standards of the institutional and/or national research committee of the participating institutions and were performed per the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This article does not contain any studies with human participants or animals performed by any of the authors.