Segmental membranous nephropathy.

Most cases of membranous nephropathy (MGN) present with global and diffuse distribution of subepithelial deposits. However, segmental MGN, in which there is focal or diffuse segmental subepithelial deposits, are occasionally encountered. The clinical and pathologic significance of segmental MGN is not well understood and thought to be more likely due to either early or resolving phase of the global form of MGN. Several case reports and literature available suggest that it may be a manifestation of secondary causes based on pathologic features such as presence of C1q and mesangial deposits, extra-glomerular deposits involving tubular basement membranes, absence of PLA2R and THSD7A, IgG1 and IgG3 subclass dominance, and the presence of other co-existing renal disease. Other reports, however, suggest that some of these cases may be a variant of the primary form of MGN. In this review, we integrate what is known about segmental MGN in order to better direct interpretation of renal biopsies in which it is identified.