The short answer
Focal segmental glomerulosclerosis (FSGS) is not one single disease. It is a pattern of scarring seen in some kidney filters, called glomeruli, usually reflecting injury to specialized cells called podocytes. Different processes can produce this pattern, and treatment depends heavily on identifying the underlying cause. (PubMed)
The most useful distinction is between:
- Primary FSGS: usually associated with nephrotic syndrome and thought to involve an immune-mediated circulating factor that injures podocytes.
- Secondary FSGS: develops as a response to another problem, such as increased pressure or workload on the glomeruli, certain infections, or medications.
- Genetic FSGS: caused by inherited changes affecting podocytes or other components of the filtration barrier.
- FSGS of undetermined cause: the biopsy shows FSGS, but available clinical and genetic information does not establish a clear cause.
This classification matters because immunosuppressive treatment that may be appropriate for primary FSGS is generally not the treatment for secondary or genetic FSGS. (PubMed)
What is FSGS?
Your kidneys contain millions of tiny filtering units. Each has a glomerulus, a network of blood vessels that filters waste and excess fluid while normally keeping most blood proteins inside the bloodstream.
In FSGS, some glomeruli develop sclerosis, meaning scar tissue. “Focal” means only some glomeruli are affected, while “segmental” means only part of an affected glomerulus is scarred.
The important point is that FSGS on a kidney biopsy describes a pattern of injury rather than automatically identifying the cause. The same biopsy pattern can result from very different diseases or stresses on the kidney. (PubMed)
Primary vs secondary FSGS
Primary FSGS
Primary FSGS is generally suspected when FSGS is accompanied by nephrotic syndrome—typically substantial protein loss in the urine, low blood albumin, and often swelling.
The exact mechanism is not completely established, but abnormal circulating factors are thought to contribute to podocyte injury in some patients.
Because primary FSGS may have an immune-mediated component, immunosuppression can be appropriate after the diagnosis has been carefully established. KDIGO recommends high-dose glucocorticoids as first-line immunosuppressive treatment for adults with primary FSGS, when appropriate. (KDIGO)
Secondary FSGS
Secondary FSGS occurs when another condition or exposure places stress on the glomeruli or directly injures podocytes.
Examples include:
- Obesity and other states of increased glomerular workload
- Loss of functioning kidney tissue
- Certain viral infections
- Some medications or toxic exposures
- Other conditions that cause chronic glomerular stress
In these situations, the priority is usually to treat or remove the underlying driver and protect remaining kidney function, rather than automatically giving immunosuppressive drugs. (PubMed)
For example, reducing an underlying source of glomerular stress may be much more relevant than treating the biopsy finding itself.
Genetic FSGS is another important category
Genetic forms result from inherited changes affecting proteins involved in the kidney’s filtration barrier.
Genetic FSGS can appear in childhood or adulthood. Suspicion may increase when there is:
- A family history of kidney disease
- Early-onset disease
- Steroid-resistant proteinuria
- An unusual clinical presentation
- No convincing secondary cause
- Features suggesting an inherited kidney disorder
Genetic testing can sometimes clarify the diagnosis and prevent inappropriate exposure to immunosuppressive treatment. It can also have implications for family counseling and kidney transplantation, particularly when a living relative is being considered as a donor. (PubMed)
A genetic result also needs careful interpretation because not every detected genetic variant is necessarily disease-causing.
Why the distinction can be difficult
A kidney biopsy can show FSGS, but the appearance under the microscope does not always tell you why it happened.
Doctors usually combine:
- The amount of urine protein
- Whether nephrotic syndrome is present
- Kidney function and its trend
- Blood pressure
- Medical and medication history
- Body size and other causes of increased glomerular workload
- Infection history
- Family history
- Kidney biopsy findings
- Electron microscopy findings when available
- Genetic testing when appropriate
This is important because primary and secondary FSGS can look similar on biopsy, and no single biopsy feature reliably identifies every subtype. (PubMed)
How FSGS is managed
1. Treat the underlying cause
For secondary FSGS, management focuses on the condition causing ongoing kidney stress.
Depending on the cause, this may involve addressing:
- Excess body weight
- High blood pressure
- Medication or toxin exposure
- Viral infection
- Reduced nephron mass or another underlying kidney problem
The exact treatment therefore varies from person to person.
2. Reduce protein loss and protect kidney function
Supportive kidney treatment is important across many forms of FSGS.
This can include appropriate management of:
- Blood pressure
- Proteinuria
- Sodium intake
- Cardiovascular risk
- Kidney function and its trend
Medications that reduce proteinuria, such as an ACE inhibitor or ARB, may be appropriate for some patients, depending on blood pressure, kidney function, potassium, and other clinical factors.
These medicines should not be started, stopped, or adjusted without clinician guidance.
3. Immunosuppression for appropriate primary FSGS
When a patient has convincing primary FSGS with nephrotic syndrome, immunosuppressive treatment may be considered.
KDIGO recommends high-dose oral glucocorticoids as first-line immunosuppression for primary FSGS. For people who cannot tolerate or have contraindications to glucocorticoids, a calcineurin inhibitor such as cyclosporine or tacrolimus may be considered. (KDIGO)
These treatments require medical supervision because steroids and calcineurin inhibitors can cause significant adverse effects, including effects on blood pressure, glucose, infection risk, and kidney function.
Importantly, immunosuppression should not simply be given because the biopsy says “FSGS.” Correct classification comes first. (PubMed)
What does FSGS mean for kidney function?
FSGS can cause significant proteinuria and, in some patients, progressive loss of kidney function. But the diagnosis does not mean that kidney failure is inevitable.
The outlook depends on factors such as:
- The underlying cause
- Amount and persistence of proteinuria
- Whether remission is achieved
- Baseline kidney function
- Blood pressure control
- Response to treatment
- Genetic or secondary disease features
A single creatinine or eGFR result cannot determine an individual’s long-term prognosis. Trends over time are more informative.
Likewise, reducing proteinuria is important because persistent heavy protein loss is associated with worse kidney outcomes in primary FSGS.
What should you do after an FSGS diagnosis?
If a biopsy has shown FSGS, one of the most important questions is not simply “What medicine treats FSGS?”
Ask instead:
- Is this primary, secondary, genetic, or undetermined FSGS?
- Do I have nephrotic syndrome?
- How much protein am I losing in my urine?
- Is my kidney function stable or changing?
- Is there an identifiable underlying cause?
- Would genetic testing be useful in my situation?
- Is immunosuppression actually appropriate?
- What is the plan for monitoring proteinuria, creatinine/eGFR, blood pressure, and treatment side effects?
This approach helps avoid treating all FSGS as though it were the same disease.
When to seek prompt medical attention
Someone with FSGS should contact their medical team promptly for significant worsening of swelling, markedly reduced urine output, persistent vomiting or dehydration, severe shortness of breath, confusion, chest pain, or other acute changes.
A sudden rise in creatinine also deserves assessment because it may represent acute kidney injury, which is different from simply assuming that chronic FSGS has progressed.
Bottom line
FSGS is a pattern of kidney scarring, not a single cause. Primary, secondary, genetic, and undetermined forms can require very different management.
The most important step is therefore accurate classification before treatment. Primary FSGS with nephrotic syndrome may warrant immunosuppression, while secondary FSGS is generally managed by addressing its underlying driver and protecting kidney function. Genetic FSGS may require genetic evaluation and usually calls for a different treatment strategy. (PubMed)
A biopsy report saying “FSGS” is therefore the beginning of the diagnostic process, not the complete diagnosis.