FSGS: from pathogenesis to the histological lesion.

Focal and segmental glomerulosclerosis (FSGS) is a generic term that in the current terminology can be appropriate for identifying two conditions. First, a morphological pattern of injury characterized by the occlusion of a single or group of glomerular capillary loops by sclerotic material, indicating a precise histological lesion but with a wide range of etiological interpretations. Second, a pauci-immune renal disease called idiopathic or primary FSGS, which is a podocytopathy triggered by an endogenous cytotoxin that recognizes the podocyte as its sole target. Based on the current and past literature, we do not possess practical tools to easily provide a precise classification of an FSGS lesion, although some clues may be of help in everyday clinical practice. Reactive forms, genetic forms, adaptive forms, forms associated with a deregulation of the proliferation and forms secondary to local glomerular inflammation are the etiological classes known to be associated with the development of an FSGS lesion. However, diagnosing each single case based on clinical, serological and histological criteria is still far from easy and mostly depends on the experience of the renal team, which should involve skilled nephrologists and pathologists.