Focal segmental glomerulosclerosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Ali Poyan Mehr, M.D. [2]Associate Editor-In-Chief:’’’ Olufunmilola Olubukola M.D.[3]

Classification

FSGS can be classified as primary or secondary disease depending etiology and the course of disease. The primary cause of FSGS is unknown or idiopathic, but there are several postulations as probable causes. 80% of FSGS cases are idiopathic. Primary or Idiopathic FSGS often presents with features of Nephrotic Syndrome with associated hematuria (microscopic), hypertension and renal insufficiency. Some genetic mutations had been associated with familial idiopathic FSGS. The role of over-expression of inflammatory markers like Tumor Necrosis Factor (TNF), Interleukins had also been associated with the extent of glomerular sclerosis.

Secondary FSGS is better described. It often occurs from some glomerular injury from previous glomeruli injury and hypertrophy. Secondary FSGS presents with non-nephrotic proteinuria and with some renal insufficiency. Etiologies of Secondary FSGS include:

• Infections with HIV, HBV;
• Drugs like anabolic steroids, heroin, lithium, pamidronate, analgesics
• Conditions like sickle cell disease and obesity.
• Systemic diseases like SLE, Lupus Nephritis, IgA Nephropathy that can cause glomerular scarring can cause Secondary FSGS.
• Genetic mutations with familial mode of inheritance had also been implicated in Secondary FSGS.

Based on the proposed Columbia classification by D’Agati and colleagues in 2004, the classification of focal segmental glomerulosclerosis (FSGS) based on the morphology is as follows:

Pathological Classification of Focal Segmental Glomerulosclerosis

Variant	Location of Lesion	Distribution of Lesion	Characteristic Features
Not Otherwise Specified (NOS)	Anywhere	Segmental	Capillary lumen abolished by the segmental increase in matrix.
Perihilar Variant	Perihilar	Segmental	Presence of one or more glomeruli containing hyalinosis in the perihilar regions with or without sclerosis. Within each glomerulus, the segmental lesions must contain > 50% perihilar hyalinosis and/or sclerosis.
Cellular Variant	Anywhere	Segmental	Presence of one or more glomerulus with segmental hypercellularity of the capillary endothelium that blocks the capillary lumen, with or without foam cells and/or karryohexis.
Tip Variant	At tip domain	Segmental	One or more segmental lesions, that include tip domains. Lesions must have adhesions/confluence of podocytes with parietal or tubular cells. Tip domains are defined as 25% of tuft adjacent to the origin of the proximal tubule. Sclerosing lesions shuld be <25% of tuft, while cellular lesions should be < 50% of tuft. No perihilar sclerosis should be observed.
Collapsing Variant	Anywhere	Segmental or global	One or more glomeruli with collapse with evidence of podocyte hypertrophy and hyperplasia.

^{Adapted from D’Agati VD, Fogo AB, Bruijn JA, and Jennette JC. Pathological classification of focal segmental glomerulosclerosis. A working proposal. Am J of Kidney Dis. 2004; 43(2):368-382.}