Mcd

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Minimal change disease

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"minimal change disease" nephrotic syndrome

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Minimal Change Disease (MCD)

Definition & Overview

Minimal change disease is a form of nephrotic syndrome named for the fact that the glomeruli appear virtually normal on light microscopy - the "minimal changes" are only apparent on electron microscopy. It is the most common cause of nephrotic syndrome in children (70-90% of childhood nephrotic syndrome) but accounts for only 10-15% of nephrotic syndrome in adults, with peak incidence between 2-6 years of age.

The diagram below illustrates the glomerular schematic in MCD:

Minimal Change Disease - glomerular schematic showing normal-appearing capillary loop

Etiology

Primary (idiopathic): Most cases.

Secondary associations include:

Hodgkin lymphoma (classic association) and other lymphomas
NSAIDs and lithium use
Infections (viral upper respiratory tract infections often precede a relapse)
Allergic/atopic states (atopy in ~40% of children, 30% of adults)
Bee sting, vaccinations

Pathogenesis

The exact mechanism remains incompletely understood, but current evidence points to immune dysfunction - originally thought to be purely T-cell mediated, now with evidence for a mixed B-cell/T-cell/autoantibody process:

T-cell hypothesis: Dysregulated T cells release circulating glomerular permeability factors (cytokines such as IL-13 and IL-4) that alter the charge/structural barrier of the glomerular capillary wall. Evidence includes: response to steroids, association with Hodgkin disease, remissions during viral infections (measles) that depress cell-mediated immunity.
CD80 (B7.1) overexpression: Podocytes in MCD show increased urinary and tissue CD80, normally expressed only by dendritic cells and B cells. Urinary CD80 correlates with disease activity. CD80 on podocytes promotes dysregulated interactions with T lymphocyte antigen-4 (CTLA-4).
Anti-nephrin antibodies (newer discovery): A subset of MCD patients have circulating antibodies against nephrin, a transmembrane podocyte protein and essential slit diaphragm component. These antibodies cause podocyte injury by interfering with nephrin crosslinking, leading to breakdown of the slit diaphragm. IgG staining on immunofluorescence colocalizes with clustered nephrin.
Angiopoietin-like-4 overexpression: Associated with the proteinuric response; reduced by corticosteroids.
Charge barrier defect: Loss of glomerular polyanions contributes to proteinuria.

Harrison's Principles of Internal Medicine 22E, p. 1317-1322
Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 846
Comprehensive Clinical Nephrology, 7th Ed., p. 257

Morphology

Microscopy	Findings
Light microscopy	Glomeruli appear completely normal
Immunofluorescence	Negative, or occasional small amounts of IgM in mesangium; subtle fine granular IgG over podocytes (anti-nephrin antibody pattern)
Electron microscopy	Diffuse, uniform effacement (flattening/retraction) of podocyte foot processes with loss of slit diaphragms; microvillous transformation; NO electron-dense deposits; GBM normal

The term "fusion" of foot processes is technically a misnomer - it actually represents simplification of podocyte architecture with collapse of the central actin cytoskeleton.

Proximal tubular cells are often laden with lipid and protein (from reabsorption of filtered lipoproteins) - hence the old name "lipid nephrosis."

Key diagnostic point: Foot process effacement occurs in many proteinuric states (membranous nephropathy, diabetic nephropathy). MCD is diagnosed only when effacement is seen alongside normal glomeruli by light microscopy - it is a diagnosis by exclusion.

Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 846
Brenner and Rector's The Kidney, p. 1342

Clinical Features

Onset: Abrupt onset of full-blown nephrotic syndrome
Edema: Periorbital (especially in children), peripheral, ascites, pleural effusion
Proteinuria: Massive - average 24-hour urine protein ~10 g; predominantly albumin (selective proteinuria)
Hypoalbuminemia: Severe
Hypertension: Less common - 30% of children, 20-50% of adults
Hematuria: Microscopic in 20% of children, 33% of adults
Renal function: Usually preserved despite massive proteinuria - a characteristic feature
Atopy/allergic symptoms: 40% of children, 30% of adults
AKI: Can occur in adults, often with low serum albumin and interstitial edema (nephrosarca); must distinguish from hypovolemia
Urine sediment: Acellular (no RBC casts, no cellular casts)

Treatment

First-line: Corticosteroids

Children: Prednisone 60 mg/m²/day (max 80 mg) for 4-6 weeks, then alternate-day dosing with gradual taper
- 90% achieve complete remission within 8 weeks
- Up to 30% have a spontaneous remission, but most are treated
Adults: Response is slower but 80-90% ultimately achieve complete remission; adults are not considered steroid-resistant until after 4 months of therapy

Response Categories

Category	Definition
Complete remission	Proteinuria <0.2 mg/24h after a single course of prednisone
Steroid-dependent	Relapse as steroid dose is tapered
Frequent relapsers	≥2 relapses within 6 months of taper
Steroid-resistant	Failure to respond to steroid therapy (in children ~5% of cases)

Relapses occur in 70-75% of children after first remission; frequency decreases after puberty
Patients with steroid resistance may have FSGS on repeat biopsy (sampling error or true progression)

Second-line agents (steroid-dependent/frequently relapsing/steroid-resistant)

Cyclophosphamide: Alkylating agent; useful for frequently relapsing disease
Cyclosporine / Tacrolimus (CNIs): 3-5 mg/kg/day in divided doses; up to 90% achieve partial or complete remission, but relapse after discontinuation is common
Mycophenolate mofetil (MMF): Used after CNI therapy
Rituximab (anti-CD20): Effective for steroid-dependent disease in both children and adults; evidence also supports a B-cell role in pathogenesis
Pulse IV methylprednisolone: May be tried in truly steroid-resistant children
Brenner and Rector's The Kidney, p. 1342-1352

Prognosis

Long-term prognosis is excellent, even in steroid-dependent disease
The disease may fully resolve when children reach puberty
Adults have a similar good long-term prognosis
Persistent MCD does not typically progress to end-stage renal disease unless there is underlying/unrecognized FSGS
Podocyte changes are completely reversible after corticosteroid therapy, along with disappearance of circulating anti-nephrin antibodies

Key Distinguishing Features vs. FSGS

Feature	MCD	FSGS
Light microscopy	Normal glomeruli	Segmental sclerosis in some glomeruli
EM	Diffuse foot process effacement	Diffuse foot process effacement
Steroid response	>90% respond	Variable, often resistant
Prognosis	Excellent	Worse
Progression	Rarely to ESRD	Can progress

MCD and FSGS may represent a disease spectrum ("podocytopathy spectrum"), with MCD at the milder, more steroid-sensitive end.

Recent evidence note: A 2025 systematic review (PMID 41357184) examined histopathological subtypes in steroid-resistant nephrotic syndrome in children - FSGS was found to be the predominant pattern, supporting the clinical overlap between MCD and FSGS in steroid-resistant cases. A separate 2025 review (PMID 39352607) highlighted the association of MCD with solid neoplasms, not just hematological malignancies, expanding the secondary causes to monitor.

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