Slide 13 is a representative immunofluorescence micrograph of the immunohistology of minimal change glomerulopathy, i.e., background staining. There are occasional specimens that will have small amounts of exclusively mesangial immunoglobulin (especially IgM) or complement accumulation that can still be designated minimal change glomerulopathy. A little bit of mesangial IgM and/or C3 without ultrastructural evidence for electron dense deposits is tolerable for a diagnosis of minimal change glomerulopathy. When groups of patients with absolutely no immunofluorescence findings have been compared to those that have low levels of IgM dominant mesangial deposits without electron dense deposits, they act no differently with respect to their clinical response to steroids and long term outcomes. Well defined mesangial electron dense deposits, however, worsen the prognosis for response to steroids or spontaneous remission. Thus, if there are electron dense deposits, minimal change glomerulopathy is not an appropriate diagnoses.
The ultrastructural finding diagramed in Slide 14 are effacement of visceral epithelial foot processes and epithelial microvillous transformation. Microvillous transformation of epithelial cytoplasm often accompanies effacement. The effacement of foot processes and microvillous transformation are not specific for minimal change glomerulopathy. Foot process effacement is characteristic for minimal change glomerulopathy and is required for the pathologic diagnosis of this disease; however, this same change is present in any patient with substantial proteinuria of any cause. Therefore, the diagnosis of minimal change glomerulopathy is one of exclusion, i.e., these ultrastructural changes should be present in the absence of light microscopic, immunohistologic or other ultrastructural features of any other cause of proteinuria.
The electron micrograph in Slide 15 is from a patient with minimal change glomerulopathy and shows almost complete effacement of the visceral epithelial foot processes. There is condensation of the epithelial cytoskeleton near the basement membrane. If you don't know what this is, you can mistake it for subepithelial electron dense deposits, suggesting membranous glomerulopathy. It is actin condensation that takes place inside of visceral epithelial cytoplasm when there is effacement of foot processes, suggesting that there is movement of cytoplasmic structures during the effacement event.
