Steroid-responsive nephrotic syndrome with normal light microscopy and diffuse foot-process effacement.
Also known as: MCD, minimal change disease, nil disease, lipoid nephrosis
Overview
A podocytopathy characterized by nephrotic syndrome with normal-appearing glomeruli on light microscopy, absent immune deposits on immunofluorescence, and diffuse podocyte foot-process effacement on electron microscopy. The most common cause of nephrotic syndrome in children.
Epidemiology
Causes ~90% of nephrotic syndrome in children under age 10 and ~10-15% in adults. Peak childhood incidence age 2-6, with a male predominance in pediatrics that disappears in adults. Strong association with atopy and recent upper respiratory infections.
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Question 1RenalMedium
A 45-year-old man presents with 3 weeks of progressive lower extremity edema and frothy urine. He has a history of treated Hodgkin lymphoma 10 years ago, currently in remission. Exam shows periorbital and pitting lower extremity edema. Labs: albumin 2.1 g/dL, total cholesterol 320 mg/dL, creatinine 0.9 mg/dL. Urinalysis shows 4+ protein and no RBCs or casts. 24-hour urine protein is 6.2 g. Renal biopsy on light microscopy shows normal-appearing glomeruli; electron microscopy reveals diffuse foot process effacement. Which of the following is the most likely diagnosis?
AIgA nephropathy
BFocal segmental glomerulosclerosis
CMinimal change disease
DDiabetic nephropathy
Reveal answer & full explanation
Correct answer: C — Minimal change disease
AIgA nephropathy
BFocal segmental glomerulosclerosis
CMinimal change disease✓
DDiabetic nephropathy
Why Minimal change disease is correct
Minimal change disease (MCD) is the most common nephrotic syndrome in children
In adults, MCD is associated with NSAIDs (nonsteroidal anti-inflammatory drugs), lithium, and paraneoplastic causes — classically Hodgkin's lymphoma, where T-cell dysfunction causes podocyte damage
No hematuria or red cell casts (distinguishes MCD from nephritic syndromes)
Electron microscopy shows diffuse podocyte foot process effacement; light microscopy shows normal-appearing glomeruli
Treatment: oral corticosteroids; 90% remission in children; adults have good response but more relapses
Why the others are wrong
IgA nephropathy — a nephritic process with hematuria and dysmorphic RBCs or red cell casts; this patient has bland urine with no RBCs, and EM shows foot-process effacement without IgA deposits
Focal segmental glomerulosclerosis — the key mimic, but it shows segmental sclerosis on light microscopy and is often steroid-resistant, whereas light microscopy here is normal
Diabetic nephropathy — causes nephrotic-range proteinuria but requires longstanding diabetes with mesangial expansion and Kimmelstiel-Wilson nodules, absent here
Question 2RenalMedium
A 40-year-old male has 9 g/day proteinuria, generalized edema, serum albumin 2.0 g/dL, and hyperlipidemia. Renal biopsy electron microscopy shows diffuse podocyte foot process effacement without immune deposits. Light microscopy is unremarkable. Which of the following is the most likely diagnosis?
AMinimal change disease
BFocal segmental glomerulosclerosis
CMembranous nephropathy
DIgA nephropathy
Reveal answer & full explanation
Correct answer: A — Minimal change disease
AMinimal change disease✓
BFocal segmental glomerulosclerosis
CMembranous nephropathy
DIgA nephropathy
Why Minimal change disease is correct
Classic triad is present: normal light microscopy, negative immunofluorescence, and diffuse podocyte foot process effacement on electron microscopy.
Produces full nephrotic syndrome — heavy proteinuria (>3.5 g/day), edema, hypoalbuminemia, and hyperlipidemia.
Most common cause of nephrotic syndrome in children, but also occurs in adults as here.
Pathogenesis is linked to T-cell dysfunction with a circulating permeability factor and loss of the podocyte anionic charge barrier.
Highly steroid-responsive; corticosteroids induce remission in most patients.
Why the others are wrong
Focal segmental glomerulosclerosis — right-concept-wrong-lesion: shows segmental sclerosis on light microscopy, whereas here light microscopy is unremarkable; classically associated with HIV, heroin use, and obesity.
Membranous nephropathy — confused-with: causes nephrotic syndrome but shows subepithelial "spike-and-dome" deposits with granular IF and anti-PLA2R antibodies, not a bland picture.
IgA nephropathy — wrong-syndrome: presents as nephritic (hematuria) with mesangial IgA deposits on IF, not the immune-deposit-free nephrotic picture described.
Additional high-yield points
Secondary triggers of minimal change disease include NSAIDs and Hodgkin lymphoma.
Selective proteinuria (mostly albumin) is characteristic because the charge barrier, not the size barrier, is disrupted.
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MCD is felt to be a T-cell–mediated podocytopathy. A circulating factor (possibly anti-nephrin antibodies, IL-13, or hemopexin) alters the podocyte cytoskeleton, neutralizes the negatively charged glomerular filtration barrier, and produces selective loss of albumin into the urine. Foot-process effacement is diffuse but reversible, explaining the rapid response to corticosteroids and the absence of structural damage on light microscopy.
Clinical presentation
Symptoms
Abrupt onset (often within days) of periorbital and dependent edema
Foamy urine, weight gain, decreased urine output
Children may present with abdominal pain from ascites or peritonitis
Symptoms often follow a viral illness or allergen exposure
IgA nephropathy — Nephritic features (hematuria) usually dominate; mesangial IgA deposits
Diagnostic workup
Diagnostic criteria
In children with classic presentation (age 1-10, no hematuria, no hypertension, normal complement, normal renal function), empiric corticosteroid therapy is initiated without biopsy. Adults and steroid-resistant children require kidney biopsy showing normal LM, negative IF, and diffuse foot-process effacement on EM.
Labs
Spot urine protein-to-creatinine ratio or 24-hour urine — nephrotic range (>3.5 g/day adult; >40 mg/m²/h child)
Serum albumin (low, often <2.5 g/dL), lipid panel (elevated)
BMP — usually normal Cr; AKI can occur from intravascular volume depletion
C3, C4 — both normal (helps distinguish from membranoproliferative or lupus nephritis)
Hepatitis B, hepatitis C, HIV, ANA, anti-PLA2R (in adults) to exclude other causes
Consider age-appropriate malignancy screening in adults (lymphoma history, exam)
Imaging
Renal ultrasound only if AKI, hematuria, or suspicion of obstruction — usually normal-sized kidneys
Diagnostic algorithm
Feature
Minimal change disease
FSGS
Most common age
Children 2-6
Adults, especially Black patients
Hematuria
Rare
Common
Hypertension
Uncommon
Common
Light microscopy
Normal
Focal segmental sclerosis
EM foot-process effacement
Diffuse
Diffuse (primary) or segmental (secondary)
Steroid response
~90% in children
~30-50% in adults
Progression to ESKD
Rare
Common in untreated primary
MCD vs FSGS — overlapping presentations distinguished by biopsy and steroid response.
Treatment
First-line
Corticosteroids — prednisone 60 mg/m²/day (max 60 mg) in children for 4-6 weeks, then taper; 1 mg/kg/day (max 80 mg) in adults for up to 16 weeks
Dietary sodium restriction, fluid management
Loop diuretic (furosemide, torsemide, bumetanide) for symptomatic edema — use cautiously to avoid intravascular volume depletion
Albumin infusion before IV diuretic if severe hypoalbuminemia and refractory edema (controversial)
Pneumococcal vaccination and consideration of penicillin prophylaxis in children with hypogammaglobulinemia
Steroid-sensitive (most pediatric cases)
Remission within 4 weeks of steroid therapy
Taper over additional 2-5 months once urine protein negative
Progression to FSGS in steroid-resistant cases on repeat biopsy
PANCE pearls
Classic pediatric presentation does not require biopsy — empiric prednisone is both diagnostic and therapeutic.
Hodgkin lymphoma is the classic paraneoplastic association in adults.
Severe edema with hypoalbuminemia can precipitate intravascular volume depletion and prerenal AKI; diurese cautiously.
Children with relapse should be screened for SBP if abdominal pain develops.
Anti-nephrin antibodies have recently been described as a possible serologic marker (2022-2024 literature).
References
KDIGO 2021 — KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases (Kidney Int 2021;100:S1-S276)
IPNA — International Pediatric Nephrology Association Clinical Practice Recommendations for Steroid-Sensitive Nephrotic Syndrome (Pediatr Nephrol 2023;38:877-919)
Anti-nephrin Ab — Watts AJB et al. Discovery of autoantibodies targeting nephrin in minimal change disease (JASN 2022;33:238-252)
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