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IntroductionMembranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in the world but remains a rare disease. It has two distinct entities with the majority of cases being primary MN, characterised by autoantibodies to the podocyte protein M-type phospholipase A2 receptor (anti-PLA2R). A minority, secondary MN, are associated with disorders including malignancy, autoimmune diseases, infections and drugs. Currently patients may undergo multiple tests to identify secondary MN associations including blood tests, chest X-Rays, CT scans, endoscopy and cystoscopy. There is no universally adopted investigative profile for MN with wide variations in approach, leading to unfocused use of limited healthcare resources, anxiety/confusion for the patient and increased risk of complications from invasive tests.Accurate incidence and prevalence of the specific associations for secondary MN remains unknown given its rare nature. This information is key not only to properly prioritise investigations for patients but also to ensure limited healthcare resources are used efficiently.MethodsWe retrospectively reviewed all patients with biopsy proven Membranous nephropathy seen in two UK tertiary renal referral centres from 2000 – 2015. We included all patients with known associations of secondary MN for analysis. Simple descriptive statistics were used to determine the incidence of the various associations of secondary MN in our patient cohort. ResultsA total of 306 patients with biopsy proven membranous nephropathy were included of which 60 were confirmed secondary MN. The majority of these (36 / 60%) were suffering with autoimmune disease, with the vast majority (28 / 46.7%) found to have lupus. Malignancy was the next most common association with 15 patients (25%). Lung cancer and Prostate cancer were the most common form of cancer with 4 (6.7%) patients each followed by oesophageal cancer with 2 (3.3%) patients. AssociationNumber (%)AssociationNumber (%)Lupus28 (46.7)Liver disease1 (1.7)Polymyositis1 (1.7)Myeloma1 (1.7)Psoriasis1 (1.7)Basal Cell Carcinoma1 (1.7)Sarcoidosis1 (1.7)Oesophageal Cancer2 (3.3)Mixed connective tissue disorder1 (1.7)Lung Cancer4 (6.7)Sjogren’s1 (1.7)Lung mets, primary unknown1 (1.7)Rheumatoid Arthritis3 (5.0)Prostate Cancer4 (6.7)Penicillamine1 (1.7)Renal Cancer1 (1.7)Gold2 (3.3)MALToma1 (1.7)Myozyme ERT1 (1.7)Post Stem Cell Transplant3 (5.0)Hepatitis B1 (1.7)DiscussionOur results validate a previous study in a French cohort (Lefaucheur et al.) showing that the most common MN-associated malignancies are lung and prostate followed by gastrointestinal. However, the incidence of malignancy is likely underestimated, as many patients with malignancy and proteinuria are not subjected to a renal biopsy. Our UK cohort confirms that a wide range of autoimmune diseases provide the majority of secondary MN diagnoses, many of which can be made clinically/serologically, without more invasive investigations. Despite the discovery of anti-PLA2R many patients with MN (both primary and secondary) undergo investigations that can be uncomfortable and come with complications. Of 60 patients with secondary MN, 47 (76%) had associations diagnosed with a clear history and routine bloods tests: autoimmune disease, medication or infections. Of the malignancies, many are diagnosed without CT scan even though a large proportion of patients will have this as part of their initial workup. Further work incorporating the results from this study and by interrogating national datasets to fine tune the causes of secondary MN, as well as the association of serum anti-PLA2R, could help in determining an algorithm for a more resource-efficient pathway for the diagnosis of secondary MN. This could in turn reduce the need for many invasive investigations used for screening. ................
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