Background/Purpose : Over 50% of patients with SLE develop renal involvement but only 20% of these are found to have pure membranous lupus neprhitis (MLN) on biopsy. Few studies have addressed its pathogenesis and there is no big series describing its characteristics. Our aim is to establish the clinical characteristics, treatment and prognosis of MLN and to make international and intersocial comparisons.

Methods : Twenty-four Spanish centres and 1 in the US participated in the study. All SLE patients with biopsy proven MLN were included. Data on clinical and laboratory features, prescribed drugs, renal outcomes and survival were collected. Descriptive statistics were used to describe the main features of the series. Chi-squared distribution and Fisher test were used to analyse categorical variables and the U Mann-Whitney test for quantitative variable. A p value <.05 was considered significant. Multivariate models were built using variables that were significant in the previous univariate analysis.

Results : A total of 150 patients were included. Patients’ characteristics are shown in the table. Spaniards (.032), patients with Public Health Coverage (.031), with a lower basal serum creatinine (BSC) (0.86 Vs 1,23 mg/dl; .014), a lower basal serum albumin (2.89 Vs 3.55 g/dl; .05), without previous venous thrombosis (.036) and those who had received chloroquine (.004) or azathioprine (AZA) (.022) for MLN were more prone to achieving a final proteinuria <.05 g. Female sex (.017), a low BSC (0.85 Vs 1.39 mg/dl; .001), low CRP (4.51 Vs 22.88 mg/l; .017), not having nephrotic syndrome at diagnosis (.028) and previous treatment with AZA (.03) were predictors of final proteinuria <1 g. Patients with final doubled creatinine had a greater initial BSC (1.92 Vs 0.86 mg/dl; .005) and a lower creatinine clearance (59.23 Vs 102.2 ml/min; .016). Moreover, male sex (.001), basal high blood pressure (<.001), chronic cardiopathy (.018) and peripheral artheriopathy (.039) were risk factors for doubling BSC. Renal failure was predicted by male sex (.001), HBP (.001), active sediment (.027), nephrotic syndrome (.008), higher BSC (1.97 Vs 0.81 mg/dl; .001), higher ESR (.043) and CRP (.013) and not having received angiotensin converting enzyme inhibitors (.036). Lastly, cardiac failure (.013), ischemic cardiopathy (.001), peripheral (.013) and cerebral (.012) artheriopathy, hemodialysis (.003) and not having received hydroxychloroquine (.03) or mophetil mycophenolate (.039) for MLN predicted death. Multivariate analysis for the different outcomes showed the type of health coverage and cardiovascular disease as the main predictors of poor outcome.

Conclusion : MLN usually begins with nephrotic syndrome, high proteinuria and normal serum creatinine. Its prognosis is favourable in maintaining renal function although proteinuria usually persists over time. Cardiovascular disease and some socio-sanitary factors are related with poor prognosis.