Focal segmental glomerulosclerosis, or FSGS, is a pattern of scarring that develops in the kidney’s tiny filtering units called glomeruli. “Focal” means only some glomeruli are affected, and “segmental” means only part of each affected glomerulus is scarred. Despite this patchwork pattern, FSGS is one of the leading causes of serious kidney disease, with roughly 50% of patients progressing to kidney failure within 5 to 10 years of diagnosis.
How FSGS Damages the Kidneys
Each kidney contains around a million glomeruli, clusters of tiny blood vessels that filter waste from the blood while keeping useful proteins in the bloodstream. In FSGS, cells called podocytes, which wrap around these blood vessels and act as the final barrier in the filter, become injured. When podocytes are damaged, the filter develops gaps, and proteins that should stay in the blood leak into the urine instead. Over time, the injured areas scar over, and those portions of the kidney stop filtering altogether.
As more glomeruli scar, the remaining healthy ones work harder to compensate, which can accelerate their own damage. This creates a cycle of worsening function that, left unchecked, leads to chronic kidney disease and eventually kidney failure requiring dialysis or transplant.
Three Main Types of FSGS
Not all FSGS has the same origin. Knowing the type matters because it shapes treatment and outlook.
Primary FSGS is thought to be caused by a circulating factor in the blood, likely a signaling molecule released from outside the kidneys, that directly injures podocytes. The exact identity of this factor remains elusive, but its existence is supported by the fact that the disease can recur almost immediately in a transplanted kidney.
Secondary FSGS develops when something else puts abnormal stress on the kidneys. Common triggers include obesity, which forces the kidneys to filter a larger blood volume; infections like HIV; diabetes; sickle cell disease; and toxicity from certain drugs or illicit substances. In other cases, it follows any condition that reduces the number of working nephrons (the kidney’s functional units), forcing survivors to handle a disproportionate workload.
Genetic FSGS results from mutations in genes that code for proteins essential to podocyte structure and function. It typically appears in early childhood, though adult-onset genetic FSGS is increasingly recognized as more gene mutations are identified. Genetic FSGS generally does not respond to immune-suppressing medications, which is an important distinction for treatment planning.
Symptoms to Recognize
FSGS often announces itself through nephrotic syndrome, a cluster of problems caused by heavy protein loss in the urine. The hallmark signs include:
- Foamy urine, caused by excess protein
- Swelling (edema) in the legs, ankles, feet, and around the eyes
- Unexplained weight gain from fluid retention
Because protein loss can be gradual at first, some people have no obvious symptoms until a routine urine test picks up abnormal protein levels. As the disease progresses and kidney function declines, fatigue, reduced urine output, and high blood pressure become more common.
How FSGS Is Diagnosed
A urine test showing significant protein is usually the first clue, but a kidney biopsy is the only way to confirm FSGS. During a biopsy, a small sample of kidney tissue is examined under a microscope for the characteristic scarring pattern.
Pathologists classify what they see into five variants: not otherwise specified (NOS), which is the most common; the collapsing variant, where capillary walls collapse inward; the tip variant, where scarring occurs at the opening of the tubule; the cellular variant, marked by increased cell activity within the scarred segment; and the perihilar variant, where scarring clusters near the point where blood vessels enter the glomerulus. These variants carry different prognoses. The collapsing variant, for instance, tends to be the most aggressive, while the tip variant often responds better to treatment.
Treatment Approaches
Treatment depends heavily on the type and severity. For primary FSGS, the initial goal is to reduce protein leakage and suppress whatever immune process is driving podocyte injury. Corticosteroids like prednisone are a common first step. If steroids alone don’t produce a meaningful response, other immune-suppressing medications may be added. Some patients achieve full or partial remission, while others prove resistant and require trials of different drug combinations.
For secondary FSGS, treatment focuses on addressing the underlying cause. If obesity is the driver, weight loss can reduce the strain on glomeruli. If a drug is responsible, stopping that drug may slow or halt damage. Genetic FSGS typically does not respond to immune suppression, so management centers on controlling symptoms and protecting remaining kidney function.
Regardless of type, several supportive medications form the backbone of long-term management. Blood pressure drugs that block the renin-angiotensin system reduce the pressure inside glomeruli, which slows protein leakage and preserves kidney function. A newer class of drugs originally developed for diabetes, SGLT2 inhibitors, has shown benefit for chronic kidney disease broadly, including patients with significant protein in their urine. Statin therapy is also recommended to manage the cholesterol elevations that often accompany heavy protein loss.
Diet and Lifestyle Changes
Dietary adjustments play a real role in slowing progression. Sodium is the biggest target: the general recommendation for people with chronic kidney disease is no more than 2,300 milligrams per day, and many FSGS patients need to stay below that. Reducing sodium helps control blood pressure and limits fluid retention, both of which protect the kidneys.
Protein intake is a balancing act. Eating too much protein increases the filtering workload on already-stressed glomeruli, but eating too little can lead to muscle loss and poor nutrition. Most people with FSGS benefit from moderate protein intake tailored to their level of kidney function. A dietitian experienced with kidney disease can help calibrate the right amount based on lab results and stage of disease.
Maintaining a healthy weight, staying physically active, and avoiding nephrotoxic substances (including certain over-the-counter pain relievers like ibuprofen) are practical steps that complement medical treatment.
What Happens If FSGS Leads to Kidney Failure
When FSGS progresses to the point where the kidneys can no longer sustain life, kidney transplant is the preferred option over long-term dialysis. But FSGS carries a unique risk: the disease can come back in the transplanted kidney. A large meta-analysis found an overall recurrence rate of 38%, meaning more than one in three transplant recipients with FSGS will see the disease return in their new kidney.
Several factors increase this risk. Younger patients, both at the time of their original diagnosis and at transplant, face higher recurrence rates. A short interval between diagnosis and kidney failure, heavy protein in the urine before transplant, and receiving a kidney from a living related donor all raise the odds. In fact, the data is strong enough that some transplant teams discourage using related living donors for FSGS patients when alternatives exist. Despite these risks, transplant still offers better outcomes and quality of life than dialysis for most people with FSGS-related kidney failure.
When recurrence does happen, it can appear within hours to days of transplant, particularly in primary FSGS where the circulating factor responsible for the original disease is still present. Plasma exchange, a procedure that filters the blood to remove that factor, is one of the main strategies used to treat early recurrence and protect the new kidney.