Nephrotic Syndrome Classification and Pathology

Definition and Diagnostic Criteria

Nephrotic syndrome is defined by heavy proteinuria (≥3.5 g/day in adults; ≥1.0 g/m²/day in children), hypoalbuminemia (<3.0 g/dL in adults; <2.5 g/dL in children), and edema, often accompanied by hyperlipidemia, as defined by the American Journal of Kidney Diseases and Kidney International 1, 2

The American Journal of Kidney Diseases recommends a novel four-category classification system for Focal Segmental Glomerulosclerosis (FSGS) that fundamentally changes diagnostic and treatment approaches, including primary FSGS, genetic FSGS, secondary FSGS, and FSGS of undetermined cause 3, 4
The Kidney International guidelines state that long-term kidney survival is excellent in patients with Minimal Change Disease (MCD) who respond to glucocorticoids 5

The primary pathophysiological mechanism of nephrotic syndrome involves increased glomerular permeability to proteins due to podocyte dysfunction, as described by Praxis Medical Insights: Practical Summaries of Clinical Guidelines 2

Patients with nephrotic-range proteinuria >3.8 g/day have a 35% risk of end-stage renal disease within 2 years, according to Praxis Medical Insights: Practical Summaries of Clinical Guidelines 2
The Journal of the American Society of Nephrology reports that nephrotic syndrome carries significant thrombotic risk with 29% incidence of renal vein thrombosis and 17-28% incidence of pulmonary embolism due to loss of anticoagulant proteins 2

The American Journal of Kidney Diseases recommends genetic testing in patients with familial kidney disease or syndromic features, steroid-resistant FSGS cases, and early-onset cases or those with family history 3, 6
The Kidney International guidelines suggest that adults with nephrotic syndrome require biopsy confirmation as FSGS and membranous nephropathy are more common 5

The three most common histological types of idiopathic nephrotic syndrome are minimal change disease (MCD), focal and segmental glomerulosclerosis (FSGS), and membranous nephropathy, with relative frequencies varying significantly according to age and ethnic background of the patient 7, 8

Minimal change disease is associated with excellent long-term renal survival in patients who respond to glucocorticoids, and may be caused by a primary disorder of T cells producing a circulating factor that interferes with glomerular permeability to albumin 7, 9
Membranous nephropathy is an autoimmune disease with a high risk of venous thromboembolism, including renal vein thrombosis and pulmonary embolism 9, 10

Infections such as hepatitis B, hepatitis C, and HIV can cause secondary histological patterns similar to primary nephrotic syndrome 11, 12, 13
Systemic diseases like systemic lupus erythematosus and diabetes can also cause secondary nephrotic syndrome 10