Minimal Change Disease vs FSGS: How to Tell Them Apart
Both minimal change disease (MCD) and FSGS are podocyte diseases that present with nephrotic syndrome and foot process effacement on electron microscopy. The core axis that separates them is the pattern of injury and prognosis: MCD shows normal light microscopy with an excellent, steroid-responsive course, while FSGS shows segmental sclerosis with hypertension, possible hematuria, and progression to CKD.
How to tell them apart
| Feature | Minimal change disease | Focal segmental glomerulosclerosis (FSGS) |
|---|---|---|
| Typical patient / epidemiology | Most common cause of nephrotic syndrome in children (70-90%), peak age 2-6 years | Most common cause of nephrotic syndrome in African Americans and the most common primary cause in adults overall |
| Hematuria | No hematuria | May have microscopic hematuria |
| Blood pressure | Usually normal | Hypertension is common |
| Preceding trigger | Often preceded by a URI or allergic exposure, with sudden onset of edema | May be primary (idiopathic) or secondary to conditions such as HIV, heroin use, obesity, sickle cell disease, or reduced nephron mass |
| Light microscopy | Normal ("minimal change") | Segmental sclerosis of some glomeruli (focal and segmental) |
| Immunofluorescence | Negative | IgM and C3 deposition in sclerotic areas |
| Prognosis / course | Excellent in children; most outgrow the disease, though relapse is common and adults do worse | Progressive to CKD over years if untreated, with common recurrence after transplant (20-40%) |
| Steroid response | Highly steroid-responsive; ~90% of children respond within 8 weeks | Primary disease needs high-dose steroids, but steroid resistance occurs and requires calcineurin inhibitors or rituximab |
The reasoning
Anchor on the clinical picture first. A young child (2-6 years) with sudden nephrotic syndrome after a URI, normal blood pressure, and no hematuria is classic MCD—empiric steroids are diagnostic and biopsy is often unnecessary. Suspect FSGS when the patient is an adult or of African American descent, when hypertension and microscopic hematuria accompany the proteinuria, or when there is a secondary risk factor (HIV, heroin, obesity, sickle cell). Steroid resistance and a progressive course also point toward FSGS. When features are atypical or the disease is steroid-resistant, biopsy arbitrates: normal light microscopy with negative immunofluorescence confirms MCD, while segmental sclerosis with IgM and C3 confirms FSGS.
Key tests
- Renal biopsy with electron microscopy: both show foot process effacement, but MCD has normal light microscopy while FSGS shows segmental sclerosis of some glomeruli.
- Immunofluorescence: negative in MCD versus IgM and C3 in sclerotic areas in FSGS.
- Urinalysis: pure proteinuria without blood in MCD, whereas FSGS may show microscopic hematuria in addition to heavy proteinuria.
What they share
- Both present with nephrotic syndrome and proteinuria
- Both are caused by podocyte injury/foot process effacement seen on electron microscopy
- Both respond, at least in part, to steroids in the primary form (high-dose steroids for primary FSGS)
- Both can be treated with steroid-sparing agents such as calcineurin inhibitors when steroid resistance or frequent relapse occurs
Pitfalls
- Assuming all foot process effacement means MCD—FSGS also shows effacement on electron microscopy; light microscopy and immunofluorescence distinguish them.
- Because sclerosis in FSGS is focal and segmental, a biopsy can miss affected glomeruli and be mistaken for MCD.
- Forgetting to screen for secondary causes of FSGS (HIV, heroin, obesity, sickle cell) instead of treating it as primary disease.
- Overlooking that adult MCD carries a worse prognosis with more relapses than childhood disease.
- Reflexively biopsying every child—classic pediatric MCD is treated empirically with steroids; biopsy is reserved for atypical or steroid-resistant cases.
Practice this the way the exam tests it — on branching cases where your decisions shape the patient.