Definition and classification variants
The essence of focal segmental glomerulosclerosis (Glomerulosclerosis focalis segmentalis) lies in the selective involvement of renal glomeruli. The term "focal" means that only some of the glomeruli are involved, while "segmental" indicates that only specific areas of the vascular tuft within them are affected.
In clinical practice, several main forms of the disease are distinguished:
- Idiopathic FSGS: an independent pathology diagnosed in a subset of patients with nephrotic syndrome.
- Overlapping FSGS: develops in the setting of other primary kidney diseases, such as membranous nephropathy or Alport syndrome.
- FSGS associated with reduced renal mass: observed in reflux nephropathy or analgesic nephropathy.
- Secondary FSGS: caused by systemic factors and infections, including HIV or heroin use.
Pathogenesis and mechanisms of development
The development of the pathology is based on severe injury to podocytes, which are visceral epithelial cells. The idiopathic form is closely associated with lipoid nephrosis and is considered a potential continuation of minimal change disease.
- A key link is the detachment of podocytes from the glomerular basement membrane (GBM).
- Exposure of the basement membrane leads to a sharp increase in permeability and the deposition of plasma proteins in areas of capillary collapse.
- The process is accompanied by the accumulation of fibrin and a reaction of mesangial cells with the formation of hyalinosis and sclerosis.
- The recurrence of proteinuria after kidney transplantation indicates the circulation of a specific systemic factor.
Morphological picture and microscopy
Initial changes often affect juxtamedullary glomeruli, locating in the region of the vascular pole.
- Light microscopy: early stages may appear unchanged or show mesangial expansion and capillary loop collapse. Later, adhesions (synechiae) with Bowman's capsule are formed.
- Electron microscopy: reveals diffuse effacement of podocyte foot processes in unaffected areas and their focal detachment.
- Immunohistochemistry: deposits of IgM and the C3 component are detected in areas of sclerosis.
- Progression: over time, global glomerular sclerosis, tubular atrophy, and interstitial fibrosis develop.
Histological variants
Within the classical course, several morphological variants of the lesion are distinguished:
- "Cellular" variant: characterized by pronounced proliferation of intraglomerular cells.
- "Tip" lesion (tip lesion): damage is localized in the area of the proximal tubule origin.
- "Collapsing" glomerulopathy: differs by marked glomerular collapse and rapid progression of chronic kidney disease.
Briefly: answers to topical questions
Which infections and toxic substances can cause secondary focal segmental glomerulosclerosis?
Secondary focal segmental glomerulosclerosis can be caused by a number of infectious agents, as well as exposure to drugs and toxic substances.
Infectious causes include:
- Viruses — hepatitis B and C viruses, HIV infection, parvovirus B19, cytomegalovirus, Epstein-Barr virus.
- Intracellular bacteria — Mycoplasma.
Toxic and drug-related factors include:
- Medications — pamidronic acid, interferons, anabolic agents for systemic use, doxorubicin.
- Drugs of abuse — heroin use.
What are the main clinical manifestations of focal segmental glomerulosclerosis?
Clinical manifestations of focal segmental glomerulosclerosis include proteinuria, nephrotic syndrome, and decreased renal function.
- In secondary FSGS, proteinuria usually increases gradually, typically without the development of nephrotic syndrome.
- Severe nephrotic syndrome is possible in drug-induced and virus-associated FSGS.
- In secondary FSGS, a steady decline in renal function is noted; in morbid obesity, mild proteinuria and an increased glomerular filtration rate may occur in the early stages.
- Arterial hypertension and hematuria are uncharacteristic of classical minimal change disease, unlike FSGS and other glomerulopathies.
FSGS is "Focus on the Segment": neither the entire kidney nor the entire glomerulus is affected as a whole, but rather foci and individual capillary segments with the loss of podocyte foot processes.
Class and exam questions
Why is the disease called focal and segmental?
The name reflects the features of the lesion: "focal" means that only individual glomeruli are involved in the process, while "segmental" indicates damage to only a portion of the capillary loops within the affected glomerulus.
Which disease is closely associated with the development of idiopathic FSGS?
Idiopathic FSGS is closely related to lipoid nephrosis (podocyte minimal change disease) and is considered a stage of its evolution or a separate disease with a similar mechanism.
What immune deposits are detected in sclerotic areas?
Immunohistochemical examination reveals immunoglobulins IgM and complement C3 in the hyaline masses of sclerotic segments.
What else to study on this topic
- Global and total glomerular sclerosis
- The role of hyperinsulinemia and hyperfiltration in FSGS
- Comparison of FSGS and lipoid nephrosis at the ultrastructural level
- Differential diagnosis of the collapsing variant of FSGS
- Relationship of circulating systemic factors with relapses
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