Membranous nephritis

Membranous nephropathy (or membranous nephritis, or membranous glomerulonephritis) is an immunologic renal disorder characterized by subepithelial immune deposits in the glomerular capillary wall. The subepithelial deposits are antigen-antibody complexes. They are formed by antibodies against cationic antigens crossing the anionic glomerular barrier or by circulating antigens. Although primary membranous predominantly has subepithelial deposits, secondary membranous may be characterized by subendothelial deposits and mesangial deposits. Rheumatoid arthritis itself can be associated with secondary MN. Drugs associated with rheumatoid arthritis such as penicillamine, gold salts, and some NSAIDs (such as Diclofenac) can also be associated with membranous nephritis. Other diseases associated with MN include lupus nephritis (WHO class V), Sjögren's syndrome, sarcoidosis, Hepatitis B virus, Hepatitis C virus. The only MN with a low complement level are lupus nephritis and Hepatitis B Virus (associated with elevated transaminases, Hepatitis B antigens).

Diagnosis
Membranous nephritis can be diagnosed by histological observation. Light microscopy with H&E stain may reveal thickened capillary walls. Fluorescence microscopy may reveal immunoglobulins in a granular pattern along the capillary wall. Jones (silver stain) may reveal spikes or holes corresponding to the immune deposits. Electron microscopy reveals electron dense deposits intramembranously or in the subepithelial space.

Prognosis
The prognosis for membranous nephritis is variable. In many cases, there is spontaneous remission. Therefore, many patients will not require treatment. However, in patients who have decreasing renal function and a high level of proteinuria (nephrotic range, and often around 10g), therapy using steroids and cytotoxics may be necessary. Cyclophosphamide and steroids have been used in some studies with success. In refractory cases, ciclosporin may also be useful. Some recent studies have tried mycophenolate mofetil with success.