Minimal change disease and focal segmental glomerulosclerosis

Abstract

The denomination ‘idiopathic nephrotic syndrome’ (INS) is progressively replacing the time-honoured term ‘nephrosis’ to define a disease comprising: (a) nephrotic syndrome; (b) on renal biopsy, absence of any lesions by light microscopy and immunofluorescence (minimal change disease, MCD), or with lesions of focal and segmental glomerulosclerosis (FSG); and (c) absence of concomitant identified disease. Of note, this last element can be assessed only after sufficient follow-up, as some rare cases of MCD may herald lymphoma [1] or discovery of a solid tumour [2]. Similarly, FSG cannot be considered ‘idiopathic’ before a host of conditions have been ruled out [3]. That MCD and FSG represent the same entity has never been definitely proven [4]. FSG can be overlooked on renal biopsy [5, 6], and a transition from MCD to FSG is common in corticosteroid-resistant forms [7]. This is why paediatricians, who rarely carry out renal biopsy at first contact with a nephrotic child, consider that the sole point of interest in INS (or nephrosis — I shall use both terms) is its mode of response to corticosteroid treatment. In fact, FSG differs from MCD in many ways. Even when the glomerular tuft appears normal by standard microscopy, the glomerular size is larger in FSG than in cases which remain MCD over time [8]. Proteinuria selectivity index [9] is poor in FSG and to some extent helps predict a poor response to therapy. Finally, FSG usually develops along with tubulointerstitial damage, interstitial fibrosis and vascular lesions, in which the part played by massive proteinuria [10, 11] and by the offending substance responsible for the podocyte changes of FSG [12], remains an open question.