Unexplained severe acute kidney injury with rapid recovery of kidney function 11 months later after the start of high-dose steroid therapy.

Our patient appears to represent a previously unrecognized variant of steroid-responsive minimal change disease (MCD)/focal and segmental glomerulosclerosis (FSGS) in which severe AKI developed even though the serum albumin was essentially normal and proteinuria was minimal. This would be a paradox because the AKI of MCD/FSGS is a manifestation of severe nephrotic syndrome. To explain this paradox, it is suggested that our patient is a rare variant of a phenomenon that is well documented in steroid-responsive MCD/FSGS, specifically, glomerular permeability to large molecules is increased (accounting for the proteinuria) but decreased to small molecules (accounting for the low glomerular filtration rate). Our patient promptly recovered kidney function on steroid therapy even though he had been oliguric and dialysis dependent for nearly 11 months. The possible pathophysiologic mechanisms for this remarkable presentation and outcome are discussed.