Clinical and Morphological Prognostic Predictors in Idiopathic Membranous Nephropathy

Clinical and Morphological Predictorsfor End Stage Renal Disease in Idiopathic MembranousNephropathy

Chi-Sheng Huang1, Yen-Chao Wang1, Chi-Chih Hung1,Shih-Meng Yeh1,Hung-Chun Chen1,2

Division of Nephrology1, Department of Internal Medicine,Kaohsiung Medical University Hospital and Department of Renal Care2, Kaohsiung Medical University, Kaohsiung, Taiwan.

Short title: Prognostic predictorsfor membranousnephropathy

Correspondence to:Hung-Chun Chen, MD, PhD.

Division of Nephrology, Department of Medicine,KaohsiungMedicalUniversity,

100 Tzyou 1st Road, Kaohsiung 807, Taiwan.

TEL: 886 7 3121101 ext 7351, FAX: 886 7 3228721, E-mail:
Abstract

Aconsiderable diversity of prognosis is seen with idiopathic membranous nephropathy (IMN), anda variety of initial factors such as amount of proteinuria has been proposed as prognostic factors.However, the predictors forrenal outcome of IMN patients in Taiwan are not clear.We retrospectively reviewed82 patients diagnosed as IMN from 1986 to 2006 in KaohsiungMedicalUniversityHospital.The average creatinine and daily protein loss were 1.14 mg/dLand 7.5 gram.20.9% patients had advanced histological lesion (stage III-IV) and 58% patients received steroid and/or immunosuppresants. The renal survival was 85.8% at 5 years and 82% at 10 years.Theywere dividedinto 3 groups: the remission group(31.7%), the persistent proteinuria group(52.4%), and the ESRD group(14.6%). There were no statistical differences in age, gender, hypertension, follow-up time and daily protein loss between these three groups. ESRD group showed significantly higher BUN, creatinine, cholesterol and irregular thickening of glomerular capillary basement membrane (GBM)at presentation (p<0.01). Morphological changes such as tubulointerstitial lesions, vascular sclerosis, and focal glomerular sclerosis, did not show association with outcome. After univariate cox regression analysis, we found BUN, creatinine, GFR, albumin, cholesterol, irregular GBM thickening and steroid or immunosuppressant treatment predicted the renal outcome. However, in multivariate cox regression analysis only GFR and cholesterol were the independent risk factors. In subgroup survival analysis, patients with GFR<60ml/min/1.73m2 or cholesterol >300 mg/dl had poor renal outcome. In conclusion, we identified that the representatives of late disease course - lower GFR and higher cholesterol (>300 mg/dl) at time of biopsy are poor prognostic factors in IMN.

Key words: Membranous nephropathy, Creatinine, Cholesterol, GBM thickness
Introduction

Idiopathic membranous nephropathy(IMN) is a disorder of unknown cause which is characterized by the granular deposition of immunoglobulin G (IgG) in the subepithelial spaces and the irregular thickening of the glomerular capillary basement membrane (GBM).IMN may have a variable natural course. A number of untreated patients may experience a partial or complete remission of proteinuria, while some others may maintain renal function with fluctuation inthe amount of proteinuria, and some may progress to end-stage renal disease (ESRD).1,2The various results may be due to different baseline conditions or due to different therapeutic effects of various treatment regimen and courses.3,4Since the potential hazardous effect of therapy, such as immunosuppressants, involving in IMN, it is of importance to predict clinical outcome of every individual patient before making therapeutic decision.That is, patients with low risks may be conserved for supportive care while manyliteraturesalso emphasize the importance ofidentifying the prognostic factors in order to apply aggressive treatment to high risk patients.5-7

Several clinical factors, like gender, hypertension, advanced age and urinary protein amountat presentation had been proposed to be predictive in IMN patients in univariate analysis. However, the prognostic factors by multivariate analysis in IMN patients in Taiwan are not clear. In this study, we retrospectively evaluate the long-term renal outcome and analyze the possible risk factors from both clinical and pathological aspects in the extensive follow-up IMN patients in southern Taiwan to identify the predictors for prognosis.

Methods

Study population

We retrospectively reviewed the renal biopsy records from 1986to Julyof 2006in KaohsiungMedicalUniversityHospital and identified 146 adult patients who were histologically proved membranous nephropathy. The treatment regimens, either supportive therapy or immunosuppressive therapies, were administrated at the treating doctors’ discretion. Patients with secondary causes such as lupus nephritis or those related to hepatitis B andmalignancy were excluded from the study,and the remaining 82patients were reviewedfor their baseline characteristics andthe follow-up outcome.

To identify the possible prognostic predictors, we divided these patients into 3 groups: remission group, persistent proteinuria group, and end-stage renal disease (ESRD) group. Remission was defined as either the daily protein loss less than 150mg or a negative dipsticktest with normal serum creatinine level. Persistent proteinuria was defined as more than 1+(30mg/dL) by dipstick with variable serum creatinine level during follow-up period. ESRD was defined as the patients who required renal replacement therapy.Nephrotic state was defined as daily protein loss of more than 3.5 gram or 3+ (300 mg/dL) to 4+ (1000 mg/dL) by dipstick.The baseline data at the time of first biopsy were collected from the medical records.Simplified MDRD-GFR equation: GFR (mL/min/1.73 m2) = 186 x (Scr)-1.154 x (Age)-0.203 x (0.742 if female) was used.

Histopathological studies

The diagnosis was confirmed by immunofluorescent, light, and electron microscopic examination in all patients. The histological staging was made according to the criteria by Ehrenreich et al8. For light microscopicexamination, renal specimens were stained with hematoxylin and eosin (H&E) and periodicacid-Schiff reagent (PAS).Renal specimens were examined by two pathologistswith no knowledge of the patients’ clinical conditionto establish the diagnosis by standard pathologic methodsalone.The degree of interstitial fibrosis and tubular atrophy, vascular sclerosis, and the presence of FSGS were determined (Table 2).Under electron microscopic examination,specimens were examined with special emphasison the regular thickness of GBMand the phase of electron dense deposits. We arbitrarily classifiedspecimens showing regular thickness of GBM with synchronous electron densedeposits of single phase as GBM regular thickness type(Fig. 1), andothers having either irregularthickness of GBM or various phases of electron dense depositsas GBM irregular thickness type (Fig. 2).

Statistical analysis

Statistical analyses were performed using the chi-square test, the analysis of variance (ANOVA) test and the Kruskal-Wallis test for the analyses of parametric and non-parametric data. The Kaplan-Meier and cox regression survival analysis were used for renal outcome. Values were expressed as mean ±standard error of mean (SEM). p value of less than 0.05 was considered statistically significant.

Results

Patients’ backgrounds

At the time of renal biopsy, 62 (76.5%) patients were in thenephrotic state (Table 1). The mean daily protein loss was 7.5 gram. The mean blood urea nitrogen was 18.0 mg/dL, serum creatinine was 1.14mg/dL, andhemoglobin level was 13.0gm/dL. Advanced histological lesion (glomerular stage III-IV) was observed in 20.9% of patients at the time of renal biopsy. Steroid and/orimmunosuppresants were prescribed to 58% of patients after renal biopsy.After a mean follow up of 58.4 months,two patients died due to sepsis. The renal survival was 85.8% at 5 years and 82% at 10 years.

Long-term outcome events

During follow-up, remission state developed in 27 (32.9%) patients with a mean duration of 69.8±44.5 months (Table 3).In the 43 (52.4%) proteinuria patients, five patients experienced temporaryremission of proteinuria but relapsed thereafter and 38 patients had persistent overt proteinuria.ESRD with need of renal replacement therapy developed in 12 patients (14.6%) after a mean follow up of 58.6 months.

Clinical and morphological characteristics in different outcome groups

To evaluate the possible prognostic predictors, we assign all patients into 3 groups: the remission group, the persistent proteinuria group, and the ESRD group. There are no statistical differences in age, gender, hypertension, follow-up time and daily protein loss (DPL) between the three groups (Table 3). Clinically, ESRD group show significantly higher BUN, serum creatinine, cholesterol and lower GFR at presentation (p<0.001). There was no significant association between treatment regimens and outcome (Table 3).

For the morphological analysis, there was no significant difference in the histological score or stagesamong three groups (Table 4).However,there were more patients showing irregular thickening of GBM in ESRD group (P=0.029).

Risk factors and survival curve for ESRD

The estimated probability of renal survival based on the Kaplan-Meier analysis was 85.8% at 5 years and 82% at 10 years. After univariate cox regression analysis, we found BUN, creatinine, MDRD-GFR, albumin, cholesterol, irregular GBM thickening and steroid or immunosuppressant treatment predict the renal outcome (Table 5). However, in multivariate cox regression analysis using the significant variates in univariate analysis, we found that only MDRD-GFR and cholesterol were the independent risk factors (Table 5). In subgroup analysis using GFR > 15 ml/min/1.73m2patients showed similar results (data not shown). Figure 3, 4 and 5 showed the different Kaplan-Meier curves for renal survival according to MDRD-GFR, cholesterol level and irregular GBM thickening at presentation.When we set the cut off cholesterol level at 300 mg/dl, all the patients with cholesterol < 300 mg/dl did not enter ESRD. (Figure 4) The patients with GFR < 60 ml/min/1.73m2 or GBM irregular thickening had poor renal outcome. (Figure 3 and 5).

Discussion

In this study, we have found that lower GFR and higher cholesterol level at presentation are prognostic predictors. Also the patients below the cut off value of cholesterol 300 mg/dlat presentation did not enter dialysis.A number of factors had been claimed to be able to predict the renal course of IMN. It is not surprised that lower GFR at presentation, which may be the result of prolonged diseases course, has been found as a risk factor for ESRD.9,10In the early CKD stage subgroups(stage 1-3 or stage 1-4), we also found that GFR is still a prognostic factor. Some studies also measure the decline of renal function (GFR slope) as an outcome but our data are not complete enough to perform accurate analysis. These data all agree that IMN patients should be identified and treated earlier.

There has been some controversy regarding the prognostic role of proteinuria. Some investigators found that the amount of proteinuria at presentation could predict the outcome of MN9,11, while others did not.12,13In this study, we did not find the significant effect of the amount of proteinuria or hypoalbuminemia on renal prognosis.Cattran et al14elaborated that patients showing normal serum creatinine with proteinuria less than4 g/day over 6 months may be considered to have a low risk of progression, and those with abnormal or deteriorating serum creatinine and/or proteinuria more than 8g/day over 6 months should be considered at high risk for progression.The persistent and long term proteinuria is more important and prognostic than short term proteinuria. Although we did not have the long term daily protein loss data, we have found that higher serum cholesterol level at presentation is a poor prognostic predictorfor IMN. Hypercholesterolemiais a consequence of increased hepatic lipoprotein synthesis that is triggered by reduced oncotic pressure and may be compounded by prolonged and increased loss of urinary proteins.15,16The high serum cholesterol level might speak for the prolonged and persistent proteinuria and the delayed visit for these patients.These again emphasize on that early diagnosis and treatment are the key to preserve renal function.

Hypercholesterolemia of the nephrotic syndrome (NS) is a risk factor for the development of systemic atherosclerosis, but it also may aggravate glomerulosclerosis by oxidized low density lipoprotein (LDL) as our previous study in focal segmental glomerulosclerosis (FSGS).17Hypercholesterolemia might deteriorate renal function in NS especially due to FSGS which could be treated by LDL-apheresisif refractory to steroids and immuosuppresant.18 Whether hypercholesterolemia is a pathogenic factor in IMN is not known. Finally, we found that a clear cut off value of cholesterol at 300 mg/dl may be a useful clinical indicator for predicting renal outcome. Due to the data limitation, we could not further analyze the lipid profile for these patients, and arandomized prospective trialapplying lipid lowering agent is needed to confirm this result.

Ehrenreich et al first described the evolution of glomerular capillary lesions ofIMN into four stages: initial subepithelial dense deposits (stage I); a subsequent GBM spike response (stage II); eventual incorporation of the deposits within the GBM (stage III); and finally formation of obviously thickened GBM (stage IV).There was no convincing evidence that the stage may predict the outcome19.In our study, we also did not find that the advanced stage (stage III, IV) predict ESRD.Recent studies suggested that tubulointerstitial lesions, vascular sclerosis, and focal sclerosis were associated with poor renal survival20,21.However, these changes did not predict the outcome independently in our study. Another probable prognostic histologic lesion is irregular thickening of GBM. GBM irregular thickening or heterogeneous electron dense deposit might indicate the increased turnover of GBM (both degradation and synthesis). A transient andself-limiting MN such as Heymann nephritis in animal models, or human secondary MN caused by drugs might be associated with regular thickening of GBM. On the other hand, irregular thickening of GBM might suggest a prolonged and increased immune activity in MN as proposed by Yashimoto et al22.

In conclusion, we have identified the representatives of late disease course - lower GFR andhigher cholestrolat time of biopsy arepoor prognosticfactors in IMN.Patients with serum cholesterol > 300 mg/dl cut off value had significantly higher risk of ESRD.
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Table 1. Baseline characteristics of patients with idiopathic membranous nephropathy (n = 82)

Table 2. Histology finding (n = 82)

Table 3. Clinical profiles of three groups with idiopathic membranous nephropathy

＊Since the biochemistry study data are not normal distribution, the data was presented by the median value with the minimal and maximum values in the bracket