Essay from General Medicine Topic: Nephrotic Syndrome

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Nephrotic Syndrome

Essay from General Medicine

Definition

Nephrotic syndrome is a clinical constellation arising from glomerular damage that causes excessive loss of protein in the urine. It is classically defined by four cardinal features:

Proteinuria >3.5 g/24 hours (nephrotic-range)
Hypoalbuminaemia - serum albumin <2.5 g/dL
Generalised oedema (often anasarca)
Hyperlipidaemia - total cholesterol usually >180 mg/dL, with lipiduria

Serum creatinine may be variable at presentation.

Classification of glomerular disease into nephrotic and nephritic syndromes

Glomerular disease can present as either nephrotic or nephritic syndrome, with nephrotic syndrome further classified as primary or secondary. - Frameworks for Internal Medicine

Pathophysiology

Nephrotic syndrome occurs when there is impairment of glomerular charge and size selectivity, normally maintained by the glomerular basement membrane (GBM), endothelial cells, and epithelial cells (podocytes). The resultant increase in glomerular permeability allows large molecules such as albumin to escape into the urine.

Two complementary mechanisms produce oedema:

1. Underfill theory: Urinary albumin losses and reduced hepatic synthesis lead to hypoalbuminaemia. The fall in plasma oncotic pressure increases fluid flux into the interstitial spaces, activating the renin-angiotensin-aldosterone system (RAAS) and causing secondary renal sodium retention. Patients with minimal change disease typically fall into this category, with contracted plasma volume and stimulated RAAS.

2. Overfill theory: A primary renal salt retention in the distal nephron and thick ascending limb (TAL) leads to sodium and water accumulation independently of oncotic pressure. Patients with other causes of nephrotic syndrome (e.g., membranous nephropathy) often have expanded plasma volume and suppressed RAAS.

Hyperlipidaemia occurs because hypoalbuminaemia stimulates generalised hepatic lipoprotein synthesis, and because reduced plasma oncotic pressure impairs normal lipase activity - raising VLDL and LDL. Lipiduria follows as these lipoproteins leak through the damaged glomerulus, appearing as oval fat bodies and fatty casts in urine.

Clinical Features

Symptoms:

Peripheral oedema - often starting periorbitally (especially in children), progressing to anasarca
Frothy (foamy) urine from heavy proteinuria
Fatigue and dyspnoea (from pleural effusions, ascites)

Physical findings:

Hypertension (variable - common in secondary causes)
Generalised dependent pitting oedema, ascites, pleural effusions
Muehrcke's lines (paired white transverse bands on nails) from hypoalbuminaemia
Eruptive xanthomata and xanthelasma from hyperlipidaemia

Investigations

Urine:

24-hour urine protein (>3.5 g/day confirms nephrotic range); or spot urine protein:creatinine ratio (correlates gram for gram with 24-hour collection - a validated, practical alternative)
Urine microscopy: oval fat bodies, fatty casts, lipid droplets; may see waxy casts; haematuria is NOT a feature (distinguishes from nephritic syndrome)
Urine albumin:creatinine ratio

Blood:

Serum albumin (<2.5 g/dL), total protein
Fasting lipid profile (elevated total cholesterol, LDL, triglycerides)
Serum creatinine, urea, electrolytes (GFR estimation)
Blood glucose/HbA1c (screen for diabetic nephropathy)
Complement levels (C3, C4) - low in SLE nephritis, MPGN
ANA, anti-dsDNA (SLE), ANCA, anti-GBM
HBsAg, HCV antibodies, HIV serology (secondary causes)
Serum/urine protein electrophoresis (myeloma)
Anti-PLA2R antibodies (primary membranous nephropathy - positive in ~70%)

Renal biopsy: Required in most adults (exceptions: typical childhood presentation strongly suggesting minimal change disease, or clear secondary cause such as diabetic nephropathy with characteristic retinopathy). Biopsy guides specific immunosuppressive treatment and provides prognostic information.

Causes

Primary (Idiopathic) Causes

Primary glomerulonephropathies are not related to known systemic disease.

Subtype	Adults (%)	Key Features
Membranous nephropathy	25-35	Most common in white adults
FSGS	20-25	Most common in Black patients
Minimal change disease	5-15	Most common in children
MPGN	5-10	Mixed nephrotic-nephritic
IgA nephropathy	<5	Usually nephritic

1. Minimal Change Disease (MCD)

The most frequent cause of nephrotic syndrome in children (1-7 years), responsible for ~80% of childhood cases. Accounts for approximately 5-15% of primary nephrotic syndrome in adults.

Pathogenesis: The leading hypothesis involves circulating molecules - potentially from T cells or other immune cells - that injure podocytes and cause foot process effacement. Recent evidence points to overexpression of angiopoietin-like-4 and CD80 in podocytes. A subset of patients have antibodies to nephrin, a slit-diaphragm protein. The underlying trigger remains incompletely characterised.

Morphology:

Light microscopy: Glomeruli appear entirely normal (hence the name) - no proliferation, thickening, or deposits
Immunofluorescence: Negative (no immunoglobulin or complement deposition)
Electron microscopy: Diffuse effacement (fusion) of podocyte foot processes - the pathognomonic finding

Minimal change disease - PAS stained glomerulus showing normal light microscopy appearance

FIG. 12.4A: Minimal change disease. The glomerulus shows normal basement membranes and absence of proliferation (PAS stain). - Robbins & Kumar Basic Pathology

Minimal change disease - Electron microscopy showing foot process effacement

FIG. 12.4B: Electron micrograph of minimal change disease showing effacement (fusion) of foot processes (arrows). CL=capillary lumen, E=epithelial cell, M=mesangium. - Robbins & Kumar Basic Pathology

Clinical: Abrupt onset of nephrotic syndrome in an otherwise healthy child. Proteinuria is highly selective (predominantly albumin). Renal function is usually preserved. >90% of children respond to corticosteroids; relapses occur in >2/3. Adults show similar response (>80% remission) but relapses are frequent, sometimes leading to steroid dependence.

2. Focal Segmental Glomerulosclerosis (FSGS)

FSGS accounts for ~30% of all nephrotic syndrome in the United States and is the primary glomerular disorder most commonly progressing to end-stage renal disease. It is most common in Black patients (approximately 50% of glomerular disease cases), with susceptibility linked to genetic polymorphisms in APOL1.

Types:

Primary FSGS: Likely mediated by a circulating factor (cardiotrophin-like cytokine 1 is one candidate); rapid recurrence after renal transplantation supports this
Secondary FSGS: Maladaptive response to nephron loss (obesity, remnant kidney), infections (HIV - "HIV nephropathy"), heroin use, genetic mutations in podocyte proteins (nephrin, podocin - >60 genes implicated)
Collapsing glomerulopathy: A severe variant with collapse of the glomerular tuft and epithelial cell hyperplasia; particularly poor prognosis

Morphology:

Light microscopy: Focal (some glomeruli affected) and segmental (only part of each glomerulus involved) sclerosis, with obliterated capillary lumina, increased mesangial matrix, hyaline material, and foamy macrophages. Initially affects juxtamedullary glomeruli.
Immunofluorescence: Nonspecific trapping of IgM and C3 in areas of sclerosis
Electron microscopy: Diffuse foot process effacement (as in MCD), but with segmental scarring

Clinical: More resistant to steroids than MCD. It carries the highest risk of thromboembolism among primary causes. Progressive renal impairment is common, with up to 50% reaching ESRD within 10 years if untreated.

3. Membranous Nephropathy

The most common cause of primary nephrotic syndrome in white adults. Approximately 70% of cases are primary (anti-PLA2R antibody positive in ~70%), with the remainder secondary to autoimmune disease (SLE), infections (hepatitis B), medications (penicillamine, gold, NSAIDs), or malignancy (colon cancer, lung cancer).

Morphology:

Light microscopy: Uniform diffuse thickening of the GBM, with "spike and dome" pattern on silver stain (projections of GBM matrix between subepithelial deposits)
Immunofluorescence: Granular IgG and C3 deposits along the GBM
Electron microscopy: Subepithelial electron-dense deposits (immune complex deposits)

Clinical: Insidious onset, middle-aged adults. One-third undergo spontaneous remission, one-third remain with persistent proteinuria, one-third progress to renal failure. High risk of renal vein thrombosis.

Secondary Causes

Secondary glomerulonephropathies mirror the clinicopathologic patterns of primary types but arise from identifiable systemic disease or exposures:

Category	Examples
Metabolic	Diabetic nephropathy (Kimmelstiel-Wilson lesions), amyloidosis
Autoimmune	SLE (membranous lupus nephritis, Class V), rheumatoid arthritis
Infections	HIV, hepatitis B and C, syphilis, malaria (quartan), infective endocarditis, schistosomiasis
Drugs/toxins	NSAIDs, lithium, gold, penicillamine, captopril, tamoxifen, heroin
Malignancy	Hodgkin's lymphoma (MCD pattern), solid tumours - colon/lung (membranous pattern), multiple myeloma
Obstetric	Preeclampsia (resolves post-delivery)

Diabetic nephropathy: Suspect a non-diabetic cause if nephrotic syndrome occurs with normal renal function, absence of retinopathy, rapid deterioration, active urinary sediment, or short duration of diabetes.

SLE: Can produce both nephrotic (Class V - membranous) and nephritic patterns (Class III/IV - proliferative).

Complications

1. Thromboembolism

The most serious complication. The mechanism involves imbalance between pro- and antithrombotic factors: urinary loss of anticoagulant proteins (antithrombin III, proteins C and S) combined with increased hepatic synthesis of procoagulant proteins (fibrinogen, factor VIII). The most common sites are the renal veins and veins of the lower extremities. Pulmonary embolism can occur. Membranous nephropathy carries the highest thrombotic risk among primary causes.

2. Infection

Nephrotic patients are prone to infections (e.g., spontaneous bacterial peritonitis from ascites, cellulitis, pneumococcal peritonitis) due to:

Loss of immunoglobulins and complement factors in urine
Oedema fluid serving as a culture medium
Immunosuppressive treatment

Encapsulated organisms (especially Streptococcus pneumoniae) are particularly hazardous. Pneumococcal vaccination is recommended.

3. Hyperlipidaemia and Atherosclerosis

Persistent hyperlipidaemia (elevated LDL, VLDL, total cholesterol) significantly increases cardiovascular risk. Statin therapy is warranted in prolonged cases.

4. Acute Kidney Injury

Can arise from: hypovolaemia (especially in underfill MCD), renal vein thrombosis, nephrotoxic drugs (e.g., diuretics, NSAIDs), or intrinsic disease progression.

5. Malnutrition

Sustained protein loss, combined with anorexia and catabolism, leads to muscle wasting and growth retardation in children.

6. Vitamin D Deficiency and Bone Disease

Vitamin D-binding protein is lost in urine, causing hypocalcaemia and secondary hyperparathyroidism.

Management

Management combines general supportive measures with disease-specific immunotherapy guided by renal biopsy findings.

General Measures

Dietary:

Sodium restriction (<2 g/day) to reduce oedema
Protein intake: moderate restriction (0.8-1.0 g/kg/day) - high protein intake does not raise serum albumin but worsens proteinuria

Oedema management:

Loop diuretics (furosemide) are first-line. Note: hypoalbuminaemia reduces furosemide binding to plasma proteins, enlarging its volume of distribution and reducing tubular delivery - higher doses or continuous infusion may be needed
Addition of a thiazide or potassium-sparing diuretic for synergy in resistant oedema
Aldosterone antagonists (spironolactone) are useful when hyperaldosteronism is present

Proteinuria reduction:

ACE inhibitors or ARBs reduce intraglomerular pressure and proteinuria independent of blood pressure. They also combat coagulopathy, dyslipidaemia, oedema, and slow progressive renal function loss. Combination ACE + ARB is generally avoided due to hypotension and worsening renal function risk.

Lipid management:

Statins for hypercholesterolaemia in patients with prolonged or heavy disease

Anticoagulation:

Therapeutic anticoagulation (LMWH or warfarin) for confirmed thrombosis (especially renal vein thrombosis or DVT/PE)
Prophylactic anticoagulation may be considered in membranous nephropathy with very low albumin (<2 g/dL)

Infection prophylaxis:

Pneumococcal vaccination; consider prophylactic penicillin in highly susceptible children

Disease-Specific Treatment

Cause	First-Line	Second-Line / Steroid-Resistant
Minimal change disease	Oral prednisolone (1 mg/kg/day); >80% remission	Cyclosporin A, tacrolimus, mycophenolate for steroid-dependent/resistant cases
FSGS (primary)	High-dose corticosteroids (response ~25-50%)	Cyclosporin A, tacrolimus, rituximab (for recurrence after transplant)
Membranous nephropathy	Conservative management first (1/3 spontaneous remission); then cyclophosphamide + steroids (Ponticelli regimen)	Rituximab (anti-CD20, effective against PLA2R-positive disease), calcineurin inhibitors
Diabetic nephropathy	Strict glycaemic control, RAS blockade (ACEi/ARB), SGLT2 inhibitors	Finerenone (non-steroidal MRA)
SLE nephritis (Class V)	Hydroxychloroquine + immunosuppression (mycophenolate/azathioprine)	Belimumab, voclosporin

Prognosis

Prognosis depends heavily on the underlying cause:

Minimal change disease: Favourable in children (>90% respond to steroids); frequent relapses but renal failure is uncommon. Adults have a slightly worse response rate but still good long-term outcomes.
Membranous nephropathy: Variable. One-third remit spontaneously; one-third develop progressive CKD. Anti-PLA2R levels correlate with disease activity and can guide treatment.
FSGS: The most aggressive primary cause. Up to 50% reach ESRD within 10 years. Collapsing variant has a particularly poor prognosis.
Secondary causes: Prognosis follows the underlying disease. Preeclampsia resolves post-partum. Diabetic nephropathy progresses to ESRD without aggressive management.

Nephrotic vs. Nephritic Syndrome - Key Distinction

Feature	Nephrotic	Nephritic
Proteinuria	>3.5 g/day (massive)	<3.5 g/day (moderate)
Haematuria	Absent/minimal	Present (dysmorphic RBCs, RBC casts)
Oedema	Prominent, often anasarca	Present but milder
Hypertension	Variable	Usually present
Renal function	Variable	Often acutely impaired
Serum albumin	Low	Normal or slightly reduced
Mechanism	Loss of protein selectivity	Inflammatory glomerular damage

Summary

Nephrotic syndrome is a clinically significant glomerular disorder defined by heavy proteinuria (>3.5 g/day), hypoalbuminaemia, oedema, and hyperlipidaemia. Its causes range from primary podocytopathies (MCD, FSGS, membranous nephropathy) to secondary systemic disorders (diabetes, SLE, infections, malignancies). Pathophysiology centres on podocyte injury leading to loss of glomerular barrier function, with downstream consequences of oedema, thrombophilia, dyslipidaemia, and immune compromise. Renal biopsy is the cornerstone of diagnosis in adults and directs immunosuppressive therapy. Management combines supportive measures (diuretics, RAS blockade, statins, anticoagulation when indicated) with cause-specific treatment. Prognosis is most favourable in MCD and least favourable in FSGS or established diabetic nephropathy.

Sources:

Frameworks for Internal Medicine (Wilkins & Williams), Chapter 34: Renal
Robbins & Kumar Basic Pathology, Chapter 12: Kidney
Brenner and Rector's The Kidney, Chapter 50: Oedema and Diuretics; Chapter 17: Glomerular Disease
Comprehensive Clinical Nephrology, 7th Edition, Chapter 3: Pathogenesis of Glomerular Syndromes
Swanson's Family Medicine Review, Chapter on Nephrology
Goldman-Cecil Medicine, Table 107-2: Subtypes of Idiopathic Nephrotic Syndrome in Adults
Recent evidence: Interventions for steroid-resistant nephrotic syndrome in children - Cochrane Review, 2025 (PMID: 40337980)

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