The collapsing form of FSGS is a histologic variant which is characterized by mesangial hypercellularity and resultant collapse of the glomerular capillaries, as illustrated in the photo to the left. Its identification is important for prognostic reasons as it is known to progress much more rapidly than garden-variety FSGS (average time to progression to ESRD 13 months from diagnosis as compared to only 65 months). Not surprisingly these patients often have profound proteinuria.
The differential diagnosis of collapsing glomerulopathy is limited, but should include HIV ("HIV Nephropathy"), parvovirus B19 infection, hepatitis C infection, therapy with the bisphophonate pamidronate, lymphoproliferative disease, and certain autoimmune disease (e.g., lupus, Still's disease, etc). The Collapsing FSGS also occur in an idiopathic form, which is interestingly much, much more common in blacks than in whites.