📚 Lecture Overview
This lecture explores glomerular diseases, classifying them primarily into nephritic and nephrotic syndromes based on clinical presentation, pathophysiology, and laboratory findings. Understanding these syndromes is vital because they represent core mechanisms of renal injury, guiding accurate diagnostic evaluation, biopsy decisions, and targeted immunosuppressive or supportive treatments.
🎯 Key Concepts & Definitions
- Nephrotic Syndrome: A clinical syndrome defined by heavy proteinuria (>3.5 g/24h), hypoalbuminemia, edema, hyperlipidemia, and lipiduria.
- Acute Nephritic Syndrome: A presentation of glomerulonephritis characterized by hematuria, impaired renal function, oliguria, and salt/water retention.
- Proteinuria: Excretion of protein in the urine exceeding normal limits (<150 mg/24h). Nephrotic range is >3.5 g/24h.
- Microhematuria: Presence of >2 RBCs per high-power field; glomerular origin is suggested by dysmorphic RBCs, acanthocytes, or RBC casts.
- Focal vs. Diffuse: Focal affects <50% of sampled glomeruli; diffuse affects >50% (or all) glomeruli.
- Segmental vs. Global: Segmental affects part of an affected glomerulus; global involves the entire tuft.
- Podocytopathies: Diseases resulting from structural abnormalities or injury to podocytes and the slit diaphragm (e.g., Minimal Change Disease, FSGS).
📖 Main Content
1. Mechanisms of Glomerular Injury
- Most glomerulonephritis (GN) is immunologically mediated, involving loss of tolerance to native or circulating autoantigens.
- Antigen-antibody binding fixes complement, forming immune complexes (ICs) or recruiting inflammatory cells (neutrophils, macrophages).
- Cellular immunity also contributes, particularly in pauci-immune GN (e.g., ANCA-associated vasculitis) where ICs do not play a primary pathological role.
- Poorly regulated healing leads to cellular dropout, scarring, glomerulosclerosis, and chronic kidney disease (CKD).
2. Nephrotic Syndrome Pathophysiology & Complications
- Caused by a structural failure of the glomerular filtration barrier (endothelium, GBM, and podocyte slit diaphragm).
- Edema Mechanisms: Results from either underfill (low plasma oncotic pressure driving fluid out of capillaries) or overfill (primary distal nephron sodium retention via ENaC activation).
- Hypercoagulability: Altered coagulation proteins and enhanced platelet aggregation increase thrombosis risk, notably renal vein thrombosis and pulmonary embolism, especially when serum albumin drops <2 g/dL.
- Infection Risk: Low IgG levels predispose patients to polysaccharide-encapsulated organisms (Mnemonic: Some Nasty Killers Have Some Capsule Protection).
- Dyslipidemia: Increased hepatic synthesis and decreased catabolism of LDL cholesterol.
3. Key Glomerular Diseases
- Minimal Change Disease (MCD): Most common nephrotic syndrome in children. Normal light microscopy, negative immunofluorescence, but electron microscopy (EM) shows diffuse effacement of podocyte foot processes. Highly steroid-sensitive.
- Focal Segmental Glomerulosclerosis (FSGS): Characterized by focal and segmental glomerular scarring. Associated with podocytopathies, hypertension, obesity, and HIV.
- Membranous Nephropathy (MGN): Most common cause of nephrotic syndrome in adults. Associated with antibodies against PLA2R. EM shows subepithelial electron-dense deposits with "spikes" of GBM.
- IgA Nephropathy: Most common type of GN worldwide. Presents with episodic macrohematuria within a day of an upper respiratory infection. Immunostaining shows mesangial IgA and C3 deposits.
- Poststreptococcal Glomerulonephritis (PSGN): Occurs 2-3 weeks post-infection. Features diffuse proliferation, neutrophilic infiltration, and subepithelial "humps" on EM with granular IgG and C3.
- Goodpasture Disease (Anti-GBM): Autoantibodies against the $\alpha$3 chain of type IV collagen in GBM and alveolar basement membrane, causing pulmonary hemorrhage and rapidly progressive GN.
- ANCA-Associated Vasculitis: Small vessel vasculitis causing necrotizing GN with crescents. Associated with c-ANCA (PR3) and p-ANCA (MPO).
4. Management & Treatment Principles
- Supportive Therapy: Use ACE inhibitors or ARBs as first-line therapy for proteinuria and hypertension. Target SBP <120 mmHg in most adults (per SPRINT trial considerations). Use loop diuretics for edema and restrict dietary sodium (<2.0 g/day).
- Induction vs. Maintenance: Therapy aims to induce remission (induction) and maintain it (maintenance) using cytotoxic or immunosuppressive agents.
- Key Drugs:
- Prednisolone: High-dose oral or IV pulses; potent anti-inflammatory.
- Cyclophosphamide: Cytotoxic alkylating agent; risks include gonadal toxicity and hemorrhagic cystitis.
- Calcineurin Inhibitors (Cyclosporine/Tacrolimus): Block T-cell activation via IL-2 inhibition; nephrotoxic.
- Mycophenolate Mofetil (MMF): Inhibits lymphocyte expansion and antibody production.
- Rituximab: Anti-CD20 monoclonal antibody that induces B-cell lysis.
📊 Visual Learning
flowchart TD
A[Glomerular Disease] --> B[Nephrotic Syndrome]
A --> C[Nephritic Syndrome]
B --> D[Heavy Proteinuria >3.5g]
B --> E[Hypoalbuminemia and Edema]
C --> F[Hematuria and RBC Casts]
C --> G[Impaired Renal Function]
mindmap
root("Nephrotic Complications")
"Edema"
"Underfill Mechanism"
"Overfill Mechanism"
"Hypercoagulability"
"Renal Vein Thrombosis"
"Pulmonary Embolism"
"Infection"
"Low IgG Levels"
"Encapsulated Organisms"
"Dyslipidemia"
"Increased LDL Synthesis"
graph LR
A[Diagnosis] --> B[Clinical Presentation]
B --> C[Urine & Blood Tests]
C --> D{Biopsy Needed?}
D -->|Yes| E[Light Microscopy & EM]
D -->|No| F[MCD in Children / PSGN]
E --> G[Guide Treatment Plan]
F --> G
💡 Important Points to Remember
- Proteinuria Threshold: Nephrotic range is >3.5 g/24h; normal urine protein is <150 mg/24h.
- Microhematuria Rule: Glomerular bleeding is indicated when >5% of RBCs are dysmorphic/acanthocytes or when RBC casts are present.
- Infection Mnemonics: Nephrotic patients lose IgG, putting them at high risk for encapsulated bacteria (Some Nasty Killers Have Some Capsule Protection).
- IgA vs. PSGN Timing: IgA nephropathy hematuria occurs within 1 day of a respiratory infection; Poststreptococcal GN occurs 2-3 weeks after infection.
- Goodpasture Target: Autoantibodies attack the $\alpha$3 chain of type IV collagen.
- ANCA Associations: c-ANCA targets PR3 (Granulomatosis with Polyangiitis); p-ANCA targets MPO (Microscopic Polyangiitis).
- First-Line Medical Therapy: Always optimize ACE inhibitors or ARBs for patients with proteinuria and hypertension.
- Common Exam Trap: Confusing Minimal Change Disease (normal light microscopy, foot process effacement on EM) with FSGS (scarring visible on light microscopy).
⚠️ Common Exam Questions
- MCQ Trick: Examiners will describe a child with nephrotic syndrome and ask if a renal biopsy is mandatory. Trap: Choosing "yes" when the correct answer is to treat empirically with steroids, as Minimal Change Disease is presumed in children aged 2–12 without atypical features.
- Short Answer: Differentiating the timing and pathology of IgA Nephropathy versus Poststreptococcal Glomerulonephritis. Examiners test whether you know that IgA presents during an upper respiratory infection with normal complement levels, whereas PSGN presents weeks later with low C3.
- Case Vignette Trap: Presenting a patient with nephrotic syndrome who develops sudden flank pain and hematuria. Examiners test recognition of renal vein thrombosis, a frequent complication of membranous nephropathy.
📝 Quick Review Checklist
I can define the criteria for nephrotic vs. nephritic syndrome
I understand the mechanisms of edema (underfill vs. overfill)
I can differentiate between MCD, FSGS, and Membranous Nephropathy
I know the histologic and immunofluorescence findings of IgA nephropathy and PSGN
I can identify the autoantibodies involved in Goodpasture disease and ANCA vasculitis
I know the first-line pharmacotherapy for proteinuria (ACEi/ARBs) and edema (loop diuretics)
I recognize the major adverse effects of key immunosuppressive drugs