Tip variant of focal segmental glomerulosclerosis: is it truly a benign variant?

Pathogenesis of Focal Segmental Glomerulosclerosis and Related Disorders

Focal segmental glomerulosclerosis (FSGS) is the morphologic manifestation of a spectrum of kidney diseases that primarily impact podocytes, cells that create the filtration barrier of the glomerulus. As its name implies, only parts of the kidney and glomeruli are affected, and only a portion of the affected glomerulus may be sclerosed. Although the diagnosis is based primarily on microscopic features, patient stratification relies on clinical data such as proteinuria and etiological criteria. FSGS affects both children and adults and has an elevated risk of progression to end-stage renal disease. The prevalence of FSGS is rising among various populations, and the efficacy of various therapies is limited. Therefore, understanding the pathophysiology of FSGS and developing targeted therapies to address the complex needs of FSGS patients are topics of great interest that are currently being studied across various clinical trials. We discuss the etiology of FSGS, describe the major contributing pathophysiological pathways, and outline emerging therapeutic strategies along with their pitfalls.

Acute Myocardial Infarction in a Patient With Focal Segmental Glomerulosclerosis Tip Lesion: Hit With a Double Whammy

Nephrotic syndrome is associated with venous and arterial thrombotic complications and is related to the imbalance between pro-thrombotic and anti-thrombotic factors. With an underlying nephrotic syndrome, arterial thromboses are infrequent, and coronary artery thromboses are much rarer. We present the case of a young male, with nephrotic syndrome, who suffered an acute anterior wall ST-segment elevation myocardial infarction. He was subsequently diagnosed to have focal segmental glomerulosclerosis (FSGS)-tip lesion. The patient was successfully managed with thrombolysis, steroids, anticoagulation, antiplatelets, and statins.

Pathogenesis of Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is characterized by focal and segmental obliteration of glomerular capillary tufts with increased matrix. FSGS is classified as collapsing, tip, cellular, perihilar and not otherwise specified variants according to the location and character of the sclerotic lesion. Primary or idiopathic FSGS is considered to be related to podocyte injury, and the pathogenesis of podocyte injury has been actively investigated. Several circulating factors affecting podocyte permeability barrier have been proposed, but not proven to cause FSGS. FSGS may also be caused by genetic alterations. These genes are mainly those regulating slit diaphragm structure, actin cytoskeleton of podocytes, and foot process structure. The mode of inheritance and age of onset are different according to the gene involved. Recently, the role of parietal epithelial cells (PECs) has been highlighted. Podocytes and PECs have common mesenchymal progenitors, therefore, PECs could be a source of podocyte repopulation after podocyte injury. Activated PECs migrate along adhesion to the glomerular tuft and may also contribute to the progression of sclerosis. Markers of activated PECs, including CD44, could be used to distinguish FSGS from minimal change disease. The pathogenesis of FSGS is very complex; however, understanding basic mechanisms of podocyte injury is important not only for basic research, but also for daily diagnostic pathology practice.

The evolution of morphological variants of focal segmental glomerulosclerosis: a repeat biopsy-based observation

BACKGROUND

The Columbia classification employs a systematic, hierarchical approach to define five mutually exclusive variants. Studies have demonstrated differences in baseline clinical characteristics and outcomes among the Columbia classification variants. However, the evolution of the Columbia classification variants of primary focal segmental glomerulosclerosis (FSGS) is unclear. We assessed the evolution of morphological variants in FSGS based on repeat native renal biopsies.

METHODS

Twenty-four patients (18 male, 6 female) with idiopathic FSGS who underwent more than one renal biopsy were enrolled in this study; three of these patients underwent three renal biopsies. The patients' clinicopathological features were reviewed. The subtypes of FSGS (2004 Columbia classification) included the collapsing, tip, cellular, perihilar and not otherwise specified (NOS) variants. The evolution of the Columbia classification variants of primary FSGS in each patient was evaluated.

RESULTS

The interval between the first and second renal biopsy was 21.95 ± 24.33 months. No significant differences in laboratory data were noted between the first and second renal biopsy. At the first renal biopsy, 5 patients were classified with collapsing, 5 with tip, 6 with cellular, 2 with perihilar and 6 with NOS variants. At the second renal biopsy, 3 patients were classified with collapsing, 3 with tip lesion, 4 with cellular, 1 with perihilar and 13 with NOS variants. Subtype changes from the first to repeat biopsies occurred in 11 patients, 9 of which progressed from other variants to the NOS variant.

CONCLUSION

Repeat renal biopsies are a useful tool for observing FSGS histological changes. The transformation from other subtypes to the NOS variant was the most common change; these alterations were accompanied by clinical progression.