Glomerular involution in children with frequently relapsing minimal change nephrotic syndrome: an unrecognized form of glomerulosclerosis?

Global glomerulosclerosis can be divided in the vascular (obsolescent) type and the glomerulopathic (solidified) type. In biopsies from children with recurrent nephrotic syndrome owing to minimal change nephropathy (MCN), we noticed small, globally sclerosed glomeruli that appeared to be distinct from global glomerulosclerosis. These small sclerosed glomeruli are best described as involuted glomeruli. We have characterized these involuted glomeruli in detail. We studied biopsies of 18 children (11 male, 7 female) with frequently relapsing MCN and evaluated possible explanatory variables. The involuted glomeruli can be differentiated from the other types of global glomerulosclerosis. Most notable is the presence of vital podocytes and parietal epithelial cells, which have retained their staining characteristics, in between the matrix, and the absence of periglomerular and tubulo-interstitial fibrosis. We observed involuted glomeruli in 12 out of 18 biopsies; the median percentage of involuted glomeruli was 6% (range 0-33%). The percentage of involuted glomeruli correlated with age at renal biopsy and the interval between onset of disease and time of renal biopsy, but not with gender, age at onset of disease, or prednisone dose. Multivariate analysis revealed that the interval between onset of disease and time of renal biopsy was the only independent predictor. In conclusion, glomerular involution is a special form of global glomerulosclerosis. The absence of periglomerular and tubulo-interstitial fibrosis suggests a different pathogenesis. Glomerular involution is a slow process. The clinical data suggest that involution is related to the duration of the disease process.