Pure Membranous Lupus Nephritis: Description of a Cohort of 150 Patients and Review of the Literature

Abstract

Objectives

The course and long-term outcome of pure membranous lupus nephritis (MLN) are little understood. The aims of this study are to evaluate the clinical features, course, outcome and prognostic indicators in pure MLN and to determine the impact of ethnicity and the type of health insurance on the course and prognosis of pure MLN.

Methods

We conducted a retrospective review of medical records of 150 patients with pure MLN from Spain and the USA.

Results

Mean age was 34.2 ± 12.5 and 80% were women. Sixty-eight percent of patients had nephrotic syndrome at diagnosis. The average serum creatinine was 0.98 ± 0.78 mg/dl. Six percent of patients died and 5.3% developed end-stage renal disease (ESRD). ESRD was predicted by male sex, hypertension, dyslipidemia, high basal 24 h-proteinuria, high basal serum creatinine and a low basal creatinine clearance. Age, cardiac insufficiency, peripheral artheriopathy, hemodialysis and not having received mycophenolate mofetil or antimalarials for MLN predicted death.

Conclusions

Pure MLN frequently presents with nephrotic syndrome, high proteinuria and normal serum creatinine. Its prognosis is favourable in maintaining renal function although proteinuria usually persists over time. Baseline cardiovascular disease and not having a health insurance are related with poor prognosis.

Resumen

Objetivos

Los conocimientos sobre el curso y el desenlace a largo plazo de la nefritis lúpica membranosa (NLM) pura son todavía escasos. El objetivo de este estudio es evaluar las características clínicas, curso, desenlace e indicadores pronósticos de la NLM y determinar el impacto de la etnicidad y tipo de cobertura sanitaria en el curso y pronóstico de la NLM.

Métodos

Se realizó una revisión retrospectiva de las historias de 150 pacientes con NLM de España y Estados Unidos.

Resultados

La edad media fue 34,2 ± 12,5 y el 80% eran mujeres. El 68% de los pacientes tenían síndrome nefrótico al diagnóstico. La creatinina sérica media fue 0,98 ± 0,78 mg/dl. El 6% de los pacientes fallecieron y el 5,3% desarrollaron insuficiencia renal terminal (IRT). El sexo masculino, la hipertensión, la dislipemia, la alta proteinuria basal, la alta creatininemia y un aclaramiento de creatinina reducido predijeron el desarrollo de IRT. La edad, la insuficiencia cardíaca, la arteriopatía periférica, la hemodiálisis y el no haber recibido micofenolato de mofetilo o antimaláricos predijeron el fallecimiento.

Conclusiones

La NLM pura suele debutar con síndrome nefrótico, alta proteinuria y creatininemia normal. Su pronóstico es favourable en términos de mantenimiento de la función renal aunque la proteinuria habitualmente persiste durante el seguimiento. La enfermedad cardiovascular basal y no tener cobertura sanitaria se relacionan con mal pronóstico.

Introduction

Over 50% of patients with systemic lupus erythematosus (SLE) have clinically significant renal involvement during the course of their disease. Approximately 8–20% of these are found on renal biopsy to have membranous lupus nephropathy (MLN).1, 2 Pure MLN has distinct histologic features compared to proliferative lupus nephritis.³ This difference is reflected in the clinical presentations of proliferative and membranous lupus nephritis, with the former being dominated by a nephritic process whereas MLN is characterised predominantly by nephrotic syndrome.1, 4, 5

Few studies have addressed the course and outcome of MLN directly,4, 6, 7, 8, 9, 10, 11, 12, 13, 14 and their results are contrasting. Most of our knowledge is derived from extrapolations of data of idiopathic membranous nephritis and/or proliferative lupus nephritis. Research on MLN frequency, natural history, prognosis and treatment was further limited due to a lack of uniform definition over the past several decades, making it difficult to get consistent information from the published literature about MLN.¹

An Italian study¹⁵ has reported the outcome in 103 patients with MLN, but a third of them had mixed forms. More recently, Mejía-Vilet et al.¹³ have reported the results of a cohort of 60 Hispanic and Mexican-mestizo patients with pure MLN suggesting an impact of ethnicity on the response to different immunosuppressants (azathioprine, cyclophosphamide or mycophenolate).

Large cohorts of patients with pure MLN are lacking, and to date the influence of ethnicity and social conditions on pure MLN outcome has rarely been studied.

The aims of the present study are to evaluate the clinical features, course, outcome and prognostic indicators in pure MLN and to explore the association of ethnicity, socio-economic level, country of residence and the type of health insurance with the course and prognosis of pure MLN.