Nephrotic Syndrome

Slide 1 · Nephrotic Syndrome

Glomerular permeability, systemic consequences, and clinicopathologic classification

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Define the nephrotic syndrome and distinguish it from isolated proteinuria.

Trace glomerular protein leakage to hypoalbuminemia, edema, lipid abnormalities, and complications.

Classify major primary and systemic causes using age and morphology.

Interpret the roles of light, immunofluorescence, and electron microscopy.

Slide 3 · Nephrotic syndrome is a clinical pattern, not one disease

Multiple glomerular lesions can produce the same permeability phenotype.

The shared functional lesion is increased glomerular capillary permeability to plasma proteins.

Etiology, microscopic pattern, renal function, and prognosis vary among causes.

A clinical syndrome directs the search for an underlying glomerular or systemic disease.

Slide 4 · The four cardinal manifestations

Heavy

Proteinuria

Hypo-

Albuminemia

Generalized

Edema

Hyperlipidemia

And lipiduria

A linked set of findings; Edema and dyslipidemia arise downstream of glomerular protein leakage.

Slide 5 · Core diagnostic thresholds

Heavy proteinuria

Hypoalbuminemia

Daily loss ≥3.5 g of protein

Pediatric thresholds differ

Plasma albumin <3 g/dL

Interpret alongside edema and lipid findings

Nephrotic-range proteinuria alone does not establish the complete syndrome.

Slide 6 · Nephrotic-range proteinuria is not synonymous with the syndrome

“Nephrotic range” describes the magnitude of protein excretion.

“Nephrotic syndrome” describes proteinuria with the characteristic systemic biochemical and clinical constellation.

Severity of edema and dyslipidemia does not map perfectly to any single protein measurement.

An underlying lesion remains to be identified.

Slide 7 · Three layers form the glomerular filtration barrier

Capillary blood

Urinary space

Fenestrated

Endothelium

Glomerular

Basement

Membrane

Podocyte

Slit

Barrier

Water + small solutes

Albumin retained

Schematic: Compartments and barrier function; Not an electron micrograph.

Slide 8 · Fenestrated endothelium permits high-volume ultrafiltration

The endothelial layer contains fenestrae allowing passage of water and small solutes.

Endothelium is the blood-facing component of the capillary filtration wall.

Normal barrier function depends on coordinated endothelial, basement-membrane, and podocyte integrity.

Protein restriction cannot be assigned to the endothelial layer alone.

Slide 9 · GBM matrix contributes to selective permeability

The glomerular basement membrane contains type IV collagen, laminin, and proteoglycans.

Its extracellular matrix supports the structural integrity of capillary loops.

Size- and charge-dependent restriction arise from the composite filtration barrier.

Changes in matrix architecture can accompany proteinuric glomerular disease.

Slide 10 · Podocyte slit diaphragms form a distal protein barrier

Interdigitating podocyte foot processes delimit filtration slits.

Slit diaphragms bridge these spaces and maintain selective protein restriction.

Nephrin, podocin, and associated proteins connect the junction to the actin cytoskeleton.

Podocyte injury or defective slit architecture can cause severe proteinuria.

Slide 11 · The normal filter discriminates by size and charge

Size selectivity

Charge selectivity

Larger plasma proteins are less permeable

Slit diaphragm is a distal size-selective barrier

Anionic albumin is normally excluded

Glomerular barrier properties restrict anionic proteins

The intact filtration wall as a combined size- and charge-selective barrier.

Slide 12 · Loss of barrier integrity permits albumin escape

Capillary blood

Urinary space

Fenestrated

Endothelium

Glomerular

Basement

Membrane

Podocyte

Slit

Barrier

Excess protein passage

Albumin leakage

Schematic: Compartments and barrier function; Not an electron micrograph.

Slide 13 · Structural and physicochemical injury converge on proteinuria

Different initiating lesions can share the same final pathway.

Structural or

Physicochemical alteration

Increase in glomerular

Protein permeability

Protein escape into

Urinary space

Heavy urinary losses are dominated by albumin, with variable globulin excretion.

Slide 14 · Protein selectivity reflects the filtration lesion

Highly selective

Poorly selective

Mainly lower-molecular-weight proteins

Albumin and transferrin predominate

Often seen with minimal change disease

Larger globulins accompany albumin

Reflects broader permeability

Often seen with FSGS or membranous disease

Slide 15 · Urinary protein loss is mainly albumin

Albumin represents the largest proportion of urinary protein loss in many nephrotic patients.

Globulins are also excreted when the filter becomes poorly selective.

The molecular-weight composition of urine protein provides clues to filtration-barrier injury.

Protein loss has both plasma-concentration and systemic consequences.

Slide 16 · Proteinuria overwhelms hepatic compensation

Net albumin balance determines circulating albumin concentration.

Urinary albumin

Loss increases

Hepatic albumin

Synthesis cannot keep pace

Plasma albumin

Concentration falls

Increased renal catabolism of filtered albumin additionally contributes to hypoalbuminemia.

Slide 17 · Tubular handling of filtered albumin adds to depletion

Filtered albumin may be reabsorbed and catabolized by renal tubules.

Increased renal catabolism is an additional mechanism of hypoalbuminemia.

Tubular protein droplets may accompany marked glomerular protein leakage.

The major driver of circulating albumin depletion remains heavy proteinuria.

Slide 18 · Hypoalbuminemia lowers plasma oncotic pressure

Albumin contributes substantially to intravascular oncotic pressure.

Loss of circulating

Albumin

Reduced plasma colloid

Osmotic pressure

Movement of fluid toward

Interstitial compartments

The clinical result is soft, pitting edema—often periorbital or dependent.

Slide 19 · Two processes amplify nephrotic edema

Fluid redistribution

Renal sodium–water retention

Reduced plasma oncotic pressure

Fluid shifts toward interstitium

Intravascular underfilling may occur

Renin–aldosterone stimulation

Sympathetic activity / reduced natriuresis

Further expands edema

Both are mechanisms; Their relative importance can vary.

Slide 20 · Renin–aldosterone signaling can aggravate edema

A compensatory response can intensify edema.

Reduced effective

Circulating volume

Renin release and

Aldosterone stimulation

Renal sodium and

Water retention

The textbook also identifies sympathetic activity and reduced natriuretic influences.

Slide 21 · Other neurohumoral pathways encourage retention

Enhanced sympathetic nervous system activity supports renal salt and water conservation.

Reduced secretion of natriuretic factors can diminish sodium excretion.

These responses interact with changes in effective intravascular volume.

The net effect is increased extracellular fluid accumulation.

Slide 22 · Edema distribution has a physiologic basis

Periorbital swelling is a characteristic early or prominent location.

Dependent tissues accumulate fluid under the influence of gravity.

Soft, pitting edema reflects freely mobile interstitial fluid.

Distribution and severity depend on oncotic pressure, salt balance, and posture.

Slide 23 · Severe hypoalbuminemia may cause serous effusions

Reduction of plasma oncotic pressure may lead to clinically important third-spacing.

Pleural effusions may accumulate around the lungs.

Ascites may develop when fluid collects in the peritoneal cavity.

These findings are consequences of systemic fluid imbalance—not separate glomerular lesions.

Slide 24 · Nephrotic dyslipidemia affects multiple lipoproteins

Cholesterol and triglyceride levels are often increased.

Very-low-density and low-density lipoproteins may rise.

Lipoprotein(a) and apoprotein concentrations may also increase.

High-density lipoprotein concentration can decrease in some patients.

Slide 25 · Hyperlipidemia has more than one mechanism

The combined disturbance yields elevated circulating cholesterol and triglycerides.

Increased hepatic

Lipoprotein synthesis

Abnormal transport of

Circulating lipoproteins

Reduced lipid

Catabolism

It is not explained solely by albumin synthesis in the liver.

Slide 26 · Altered lipid transport sustains circulating lipoproteins

The dyslipidemic state reflects disturbed synthesis, distribution, and clearance.

Changes in apoproteins and transport contribute to the altered plasma profile.

Lipid abnormalities can persist while urinary protein loss remains heavy.

Interpret lipid changes as part of the systemic response to nephrosis.

Slide 27 · Hyperlipidemia and a leaky barrier cause lipiduria

Lipiduria arises from combined plasma and glomerular abnormalities.

Circulating

Lipoproteins increase

Lipoproteins cross the

Damaged filtration barrier

Lipids appear

In urine

Urinary lipid may be free fat or contained in exfoliated tubular epithelial cells.

Slide 28 · Oval fat bodies reflect tubular uptake of lipid

Filtered lipoproteins are reabsorbed by tubular epithelial cells.

Lipid-laden tubular cells may detach and enter urinary sediment.

Such cells appear as oval fat bodies in a nephrotic urine sample.

Their presence reflects lipid handling downstream of glomerular leakage.

Slide 29 · Clinical findings form one causal network

Glomerular

Protein leakage

Albumin

Depletion

Fluid

Accumulation

Lipid and systemic

Complications

Permeability defect is upstream; Later features are linked but not identical.

Slide 30 · Urinary immunoglobulin loss increases infection risk

Loss of plasma proteins can include immunoglobulins.

Reduced host-defense components contribute to susceptibility to infection.

Nephrotic patients may be particularly vulnerable to bacterial infections.

Infection risk is a systemic complication, not simply a urinary tract issue.

Slide 31 · Staphylococcal and pneumococcal infections merit attention

Robbins specifically highlights staphylococcal infections.

Pneumococcal infections are another characteristic concern.

Protein losses provide a plausible link between nephrosis and impaired humoral defense.

A febrile patient with active nephrosis should not be assessed as having edema alone.

Slide 32 · Nephrosis can create a hypercoagulable state

Loss of endogenous anticoagulants contributes to increased thrombotic risk.

Antithrombin III is a specifically described urinary loss.

Thrombotic and thromboembolic complications occur in nephrotic patients.

Proteinuria therefore produces consequences beyond low oncotic pressure.

Slide 33 · Urinary antithrombin loss can promote thrombosis

The renal lesion can alter systemic hemostasis.

Loss of anticoagulants

In urine

Impaired endogenous

Anticoagulant activity

Greater risk of

Thrombotic complications

Antithrombin III loss is one contributor; It is not the only determinant of risk.

Slide 34 · Renal vein thrombosis: Complication rather than primary cause

Renal vein thrombosis was historically regarded as a possible cause of nephrosis.

It is usually a consequence of the hypercoagulable state.

The association is particularly important in membranous nephropathy.

Do not invert the causal direction when interpreting nephrotic presentations.

Slide 35 · Four domains of nephrotic morbidity

Fluid overload

And effusions

Dyslipidemia

And lipiduria

Infection

Susceptibility

Venous thrombosis

And embolism

All trace back to glomerular injury and its biochemical/systemic effects.

Slide 36 · Classify causes as primary or associated with systemic disease

Nephrotic syndrome

Primary glomerular lesions

Minimal change disease

Membranous nephropathy

Primary FSGS

Systemic associations

Diabetes · Amyloidosis · SLE

Drugs · Infections · Malignancy

The list is representative, not exhaustive.

Slide 37 · Age changes the differential diagnosis

In North American children, nephrosis is usually due to a primary glomerular lesion.

Systemic disease is a relatively more important source in adults.

Minimal change disease dominates childhood primary patterns.

Membranous nephropathy and FSGS become more prominent in adult etiologic assessment.

Slide 38 · Primary childhood patterns: Use age to prioritize

Textbook estimates for primary causes in children; Do not generalize across populations.

Lesion

Approximate share*

Teaching implication

Minimal change disease

75%

Most frequent primary lesion

FSGS

10%

Significant alternative

Membranous nephropathy

3%

Relatively uncommon

MPGN / other GN

≈12% combined

May show mixed manifestations

Slide 39 · Adult primary lesions show a different distribution

Textbook composite estimates among primary causes; Systemic disease is separately considered.

Lesion

Approximate share*

Interpretive point

FSGS

35%

Common adult pattern

Membranous nephropathy

30%

Important adult lesion

Minimal change disease

8%

Less dominant than in children

MPGN / other GN

≈27% combined

May overlap nephritic pattern

Slide 40 · Three primary lesions: Distinguishing pathology

These are prototypic morphology patterns, not stand-alone diagnoses.

Disease

Light microscopy

Electron microscopy

Minimal change

Glomeruli often normal

Diffuse foot-process effacement

Membranous

Capillary-wall thickening

Subepithelial deposits

Primary FSGS

Focal segmental sclerosis

Effacement; Podocyte loss

Slide 41 · Minimal change disease: LM can appear normal

No conspicuous glomerular lesion on LM

Simplified morphology schematic — not a clinical/histologic specimen

Slide 42 · Minimal change disease centers on podocyte injury

Anti-nephrin antibodies are implicated in a subset of cases.

Podocyte slit-diaphragm

Dysfunction

Diffuse foot-process

Effacement

Often highly selective

Proteinuria

The classic EM picture lacks electron-dense immune-complex deposits.

Slide 43 · Membranous nephropathy: Subepithelial deposits

Subepithelial deposits

Simplified morphology schematic — not a clinical/histologic specimen

Slide 44 · Membranous nephropathy links deposits to barrier injury

PLA2R is a major antigen in primary membranous nephropathy.

Antibodies react with

Target antigens

Subepithelial

Immune deposits form

Capillary walls thicken

And proteinuria develops

Granular immunoglobulin/complement staining and GBM spikes support the lesion.

Slide 45 · FSGS: Sclerosis is both focal and segmental

Segmental

Sclerosis

Unaffected

Portion

Simplified morphology schematic — not a clinical/histologic specimen

Slide 46 · FSGS progresses from podocyte loss to sclerosis

Focal: Only some glomeruli; Segmental: Only part of an affected tuft.

Podocyte damage

And detachment

Areas of exposed

Glomerular basement membrane

Hyalinosis and

Segmental sclerosis

Primary FSGS is only one etiologic category; Adaptive, genetic, and other forms exist.

Slide 47 · LM, IF, and EM answer different questions

A nephrotic clinical pattern may have very different microscopic substrates.

Method

Question

Examples

Light microscopy

What is the tissue architecture?

Normal LM in MCD; Sclerosis in FSGS

Immunofluorescence

Which immune reactants are present?

Granular IgG in membranous lesion

Electron microscopy

Where are deposits / podocyte changes?

Effacement; Subepithelial deposits

Slide 48 · Diabetes mellitus is an important systemic cause

Diabetes is among the major systemic causes of nephrotic syndrome.

The etiologic classification must therefore include non-primary renal disorders.

Clinical context and renal pathology are interpreted together.

The nephrotic phenotype does not by itself establish diabetic nephropathy.

Slide 49 · Amyloidosis belongs in the systemic differential

Amyloidosis is a frequently cited systemic association of nephrotic syndrome.

Heavy proteinuria can be the dominant renal manifestation.

A systemic disease history changes the diagnostic question from lesion pattern alone to underlying etiology.

Specific morphologic proof requires tissue evaluation, not clinical syndrome recognition alone.

Slide 50 · SLE can present with a nephrotic phenotype

Systemic lupus erythematosus is a major systemic cause listed by Robbins.

Not every lupus glomerular lesion produces the same clinical syndrome.

A membranous lesion is one mechanism of nephrotic presentation in SLE.

Clinical serology, systemic findings, and renal pathology must be integrated.

Slide 51 · Secondary causes extend beyond metabolic and autoimmune disease

Drugs include nonsteroidal anti-inflammatory drugs and penicillamine.

Infections listed include malaria, syphilis, viral hepatitis, and HIV.

Malignant neoplasms, including carcinomas and lymphoma, may be associated.

These are etiologic categories to investigate, not presumptive diagnoses.

Slide 52 · Nephrotic and nephritic patterns answer different questions

Nephrotic pattern

Nephritic pattern

Heavy proteinuria dominates

Hypoalbuminemia with edema

Hyperlipidemia / lipiduria

Hematuria with RBC casts

Oliguria or azotemia

Hypertension; Often inflammatory lesion

Some glomerular diseases generate mixed nephritic–nephrotic syndromes.

Slide 53 · Mixed nephritic–nephrotic presentations occur

Proliferative glomerular diseases may produce substantial protein loss.

Membranoproliferative patterns can combine nephritic and nephrotic manifestations.

IgA nephropathy and other proliferative lesions may also enter the differential.

Urine sediment and renal function help detect an inflammatory component.

Slide 54 · Clinical evaluation proceeds from phenotype to etiology

A conceptual diagnostic sequence, not a formal treatment guideline.

Establish heavy

Proteinuria

Assess albumin, edema,

Lipids, and complications

Integrate systemic clues

And glomerular pathology

The clinical syndrome is a starting point; Morphology and context refine the diagnosis.

Slide 55 · Quantify urine protein before attributing its cause

A measurement of daily protein excretion allows comparison with the nephrotic-range threshold.

Total protein quantity and molecular composition answer different questions.

Identify whether the urinary proteins are predominantly albumin or include larger globulins.

Interpret quantitative results alongside clinical edema and serum albumin.

Slide 56 · Urinary sediment provides mechanistic clues

Lipiduria and oval fat bodies are compatible with a nephrotic phenotype.

Red cell casts and prominent hematuria suggest a nephritic component.

Sediment characteristics do not replace etiologic diagnosis.

Tubular protein or lipid reabsorption reflects downstream effects of glomerular leakage.

Slide 57 · Laboratory findings map to the causal pathways

Finding

Underlying process

Interpretation

Heavy proteinuria

Increased permeability

Primary functional defect

Low albumin

Protein depletion / catabolism

Contributes to edema

High plasma lipids

Altered lipoprotein balance

Systemic metabolic effect

Lipiduria

Lipoprotein passage / cells

Downstream tubular effect

Slide 58 · Biopsy patterns identify the lesion, not merely the syndrome

Normal-appearing glomeruli by LM do not exclude a major podocytopathy.

IF and EM may reveal deposits or diffuse foot-process effacement.

Membranous disease illustrates immune deposits with capillary-wall changes.

FSGS illustrates loss of podocytes and formation of segmental scars.

Slide 59 · Application: A child with selective proteinuria

A preschool-aged child develops marked pitting edema, heavy predominantly albumin proteinuria, and preserved renal function.

Interpretation

Which lesion is common in this age group?

What would you expect by light and electron microscopy?

Slide 60 · Application: An adult with subepithelial deposits

An adult presents with nephrotic syndrome. Renal biopsy shows capillary-wall thickening and subepithelial electron-dense deposits.

Interpretation

Which primary glomerular lesion is suggested?

Which immunofluorescence distribution supports it?

Slide 61 · Application: Edema with renal-vein thrombosis

A patient with severe nephrotic proteinuria develops renal-vein thrombosis. The question is whether thrombosis caused the syndrome.

Interpretation

What causal direction is emphasized by Robbins?

Which urinary loss contributes to hypercoagulability?

Slide 62 · Integrated clinicopathologic reasoning

Observation

Mechanistic inference

Next interpretive step

Proteinuria + low albumin

Damaged glomerular filter

Investigate lesion

Edema

Oncotic / sodium mechanisms

Assess fluid burden

Lipiduria

Lipoprotein filtration

Correlate plasma lipids

Thrombosis

Procoagulant state

Recognize complication

Slide 63 · Link each nephrotic feature to its mechanism

Feature

Mechanistic explanation

Proteinuria

Increased glomerular capillary-wall permeability

Hypoalbuminemia

Urinary loss outstrips synthesis; Catabolism contributes

Edema

Low oncotic pressure and renal sodium retention

Hyperlipidemia

Changed synthesis, transport, and clearance

Infections / thrombosis

Loss of immunoglobulins and anticoagulants

Slide 64 · Synthesis: Phenotype, mechanism, and etiologic diagnosis

Nephrotic syndrome begins with excessive glomerular permeability to proteins.

Albumin depletion, fluid retention, lipid abnormalities, and systemic complications are interconnected.

Primary podocytopathies and deposit diseases coexist in the differential with systemic disorders.

LM, IF, and EM explain why the same clinical syndrome arises from different lesions.

Slide 65 · Principal reference

Robbins, Cotran & Kumar

Pathologic Basis of Disease

Core nephrotic syndrome discussion and glomerular disease context

Nephrotic Syndrome; adjacent sections on glomerular structure, membranous nephropathy, minimal change disease, and FSGS.