Focal segmental glomerular sclerosis (FSGS) is the most common primary glomerular disease, resulting in heavy proteinuria and leading to ESRD. The term FSGS refers to a morphologic pattern of injury rather than a distinct disease. Sclerotic lesions are present in <50% of all glomeruli on light microscopy (hence focal), with <50% of the glomerular tuft affected (hence segmental). FSGS can be primary or secondary to a variety of physiologic, anatomic, or environmental factors. Primary FSGS is characterized by rather acute onset of heavy proteinuria, with other features of the nephrotic syndrome, renal impairment, and resistance to treatment in many patients. The incidence of FSGS as cause for ESRD is increasing (1). Spontaneous remission rate is low (<5%) and progression to ESRD within a few years (5 to 8 years) of diagnosis is common (50%) in patients who do not respond to therapy (2).
There are several histologic variants described in the Columbia classification: FSGS not otherwise specified (NOS), collapsing, tip, perihilar, and cellular variants (3). In spite of initial hopes, this classification, although useful, has not consistently correlated with natural history or response to therapy. FSGS NOS is the most commonly seen variant. In general, collapsing variant has the worst prognosis, whereas tip lesion has the best prognosis and is often responsive to immunosuppressive therapy.
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