Diabetic Nephropathy

Slide 1 · Diabetic Nephropathy

Mechanisms · Glomerular pathology · Vascular lesions · Clinical correlation

Pathogenesis

Morphology

Clinical consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

OVERVIEW

Explain how chronic hyperglycemia produces glomerular and vascular injury.

Recognize basement membrane thickening, diffuse sclerosis, and Kimmelstiel–Wilson nodules.

Relate arteriolar lesions and tubulointerstitial scarring to declining renal function.

Interpret albuminuria and advanced nephropathy in clinicopathologic context.

Slide 3 · Diabetic nephropathy: Scope and definition

INTRODUCTION

Chronic diabetic kidney injury involves glomeruli, renal microvessels, and the tubulointerstitium.

Renal manifestations range from albuminuria to advanced chronic kidney failure.

The disease occurs in both type 1 and type 2 diabetes.

Diabetes mellitus

Renal microangiopathy

Glomerular injury

Chronic loss of function

Conceptual sequence — schematic

Slide 4 · The kidney is a major diabetic target organ

INTRODUCTION

The kidney is among the principal sites of diabetic microvascular injury.

Renal failure is an important contributor to diabetes-associated mortality.

Nephropathy is a leading cause of end-stage kidney disease in the United States.

Kidney injury is a systemic microvascular complication

Glomerular and microcirculatory damage predominate

Slide 5 · Three patterns of renal injury coexist

INTRODUCTION

Glomerular disease: Basement membrane thickening and glomerulosclerosis.

Vascular disease: Renal atherosclerosis and hyaline arteriolosclerosis.

Infections: Pyelonephritis, sometimes with papillary necrosis.

Glomerular lesions

Renal vascular lesions

Pyelonephritis

Distinct but coexisting renal lesions

Slide 6 · Diabetic microangiopathy provides the framework

INTRODUCTION

Small-vessel basement membranes become diffusely thickened.

The lesion is prominent in glomerular and medullary capillaries.

Thickened basement membranes are nevertheless abnormally permeable to plasma proteins.

Capillary

Thickened basement membrane

Urinary space

Stylized layered barrier — not an electron micrograph

Slide 7 · Diabetes affects multiple vascular compartments

INTRODUCTION

Large and medium arteries develop accelerated atherosclerosis.

Microvascular disease damages the retina, kidneys, and peripheral nerves.

Renal lesions include both glomerular microangiopathy and vascular insufficiency.

Macrovascular

Accelerated atherosclerosis

Microvascular

Basement membrane / small vessel injury

Teaching comparison — schematic

Slide 8 · Risk reflects metabolic exposure and host factors

INTRODUCTION

Severity of chronic complications increases with degree and duration of hyperglycemia.

Insulin resistance and obesity also contribute to diabetic tissue injury.

Not every individual with diabetes develops the same renal phenotype.

Persistent hyperglycemia

Insulin resistance / obesity

Host susceptibility

Renal injury

Convergent pathology / interacting components

Slide 9 · Persistent hyperglycemia drives chronic injury

PATHOGENESIS

Glucotoxicity increases flux through several damaging metabolic pathways.

Excess substrates produce reactive intermediates, signaling changes, and oxidative stress.

These mechanisms converge on vascular dysfunction and extracellular matrix accumulation.

Persistent hyperglycemia

Metabolic pathway activation

Vascular + matrix injury

Conceptual sequence — schematic

Slide 10 · Four metabolic pathways are implicated

PATHOGENESIS

Formation of advanced glycation end products (AGEs).

Excess diacylglycerol–protein kinase C (DAG–PKC) signaling.

Polyol-associated oxidative stress and hexosamine pathway flux.

AGE–RAGE

DAG–PKC

Polyol / ROS

Hexosamine

Each contributes a different mechanistic or structural component

Slide 11 · AGEs arise through nonenzymatic glycation

PATHOGENESIS

Reactive glucose-derived metabolites modify amino groups of proteins.

The process occurs in intracellular and extracellular compartments.

Hyperglycemia accelerates the formation of AGEs.

Excess glucose metabolites

Nonenzymatic reactions

Advanced glycation end products

Conceptual sequence — schematic

Slide 12 · AGE–RAGE signaling amplifies vascular injury

PATHOGENESIS

AGEs engage the receptor for AGEs (RAGE) on several vascular and immune cell types.

RAGE signaling promotes inflammatory and oxidative responses.

An endothelial response contributes to diabetic microangiopathy.

AGEs

RAGE on vascular / immune cells

ROS + inflammatory signaling

Conceptual sequence — schematic

Slide 13 · TGF-β signaling favors matrix accumulation

PATHOGENESIS

AGE–RAGE signaling promotes release of growth factors including TGF-β.

TGF-β enhances deposition of basement membrane and other extracellular matrix material.

Matrix expansion is a central morphologic feature of diabetic glomerular disease.

AGE–RAGE pathway

TGF-β-related signaling

Excess extracellular matrix

Conceptual sequence — schematic

Slide 14 · DAG activates the PKC signaling pathway

PATHOGENESIS

Intracellular hyperglycemia enhances de novo DAG synthesis.

Increased DAG drives excessive activation of protein kinase C.

PKC modulates vascular growth factors and procoagulant signaling.

Intracellular glucose

DAG formation

PKC activation

Conceptual sequence — schematic

Slide 15 · AGE and PKC effects overlap

PATHOGENESIS

PKC signaling promotes endothelial TGF-β and VEGF production.

PAI-1 expression is another downstream effect.

AGE-mediated and PKC-mediated processes share contributions to microangiopathy.

AGE–RAGE

DAG–PKC

TGF-β / endothelial responses

Microangiopathy

Convergent pathology / interacting components

Slide 16 · The polyol pathway consumes cellular NADPH

PATHOGENESIS

Aldose reductase converts excess glucose into sorbitol.

The pathway uses NADPH, which is also needed to maintain reduced glutathione.

Increased flux can weaken defenses against reactive oxygen species.

Excess intracellular glucose

Aldose reductase / sorbitol

NADPH consumption

Conceptual sequence — schematic

Slide 17 · Reduced glutathione is an antioxidant defense

PATHOGENESIS

Glutathione reductase requires NADPH to replenish reduced glutathione (GSH).

Less available NADPH can limit regeneration of GSH.

Oxidative stress increases when reactive oxygen species are not adequately neutralized.

NADPH diverted

Less GSH regeneration

Oxidative vulnerability

Conceptual sequence — schematic

Slide 18 · Hexosamine flux is a proposed contributor

PATHOGENESIS

Hyperglycemia increases availability of glycolytic intermediates.

Some intermediates enter the hexosamine pathway.

The textbook links enhanced flux to cellular damage and oxidative stress.

Glucose intermediates

Hexosamine pathway

Cell stress

Conceptual sequence — schematic

Slide 19 · Diverse pathways converge on renal pathology

PATHOGENESIS

Matrix deposition thickens glomerular and tubular basement membranes.

Mesangial matrix expansion remodels the glomerular tuft.

Microvascular dysfunction and ischemia compound parenchymal injury.

Matrix deposition

Mesangial expansion

Vascular narrowing

Chronic renal injury

Convergent pathology / interacting components

Slide 20 · A thick basement membrane can still be leaky

PATHOGENESIS

Diabetic capillary basement membranes are often markedly thickened.

The increase in thickness does not imply restoration of barrier selectivity.

Abnormal protein permeability helps explain urinary albumin loss.

Capillary lumen

Abnormally thick GBM

Albumin escapes

Stylized layered barrier — not an electron micrograph

Slide 21 · The renal injury spans four compartments

MORPHOLOGY

Glomerular capillary walls and mesangium.

Afferent/efferent arterioles and larger renal arteries.

Tubules and interstitium, with superimposed infection in some patients.

Glomeruli

Arterioles

Tubules

Interstitium

Each contributes a different mechanistic or structural component

Slide 22 · GBM thickening is a fundamental lesion

MORPHOLOGY

Glomerular capillary basement membrane thickening is widespread in nephropathy.

It is part of the more generalized diabetic microangiopathy.

Electron microscopy shows the change more clearly than light microscopy.

Capillary lumen

Thickened GBM

Podocyte / urinary side

Stylized layered barrier — not an electron micrograph

Slide 23 · GBM changes may precede clinical disease

MORPHOLOGY

In type 1 diabetes, measurable thickening can begin early after onset.

The source describes onset by roughly 2 years and about 30% thickening by 5 years.

Histologic changes therefore need not parallel the first clinically recognized albuminuria.

Diabetes onset

Early GBM thickening

Progressive matrix changes

Conceptual sequence — schematic

Slide 24 · Electron microscopy highlights wall thickening

MORPHOLOGY

The capillary basement membrane appears expanded between endothelial and epithelial sides.

Capillary lumina and urinary spaces provide orientation.

An image-based diagnosis must distinguish this from a native schematic.

Capillary blood

Basement membrane

Urinary space

Stylized layered barrier — not an electron micrograph

Slide 25 · Tubular basement membranes also thicken

MORPHOLOGY

Diabetic microangiopathy is not limited to glomerular capillaries.

Tubular basement membrane thickening may accompany progressive GBM changes.

Basement membrane alteration extends across several renal structures.

Glomerular wall

Capillary GBM thickening

Tubular wall

Tubular BM thickening

Teaching comparison — schematic

Slide 26 · Mesangial widening accompanies GBM injury

MORPHOLOGY

Mesangial matrix gradually accumulates between capillary loops.

Expanded mesangium alters the organization of glomerular lobules.

Persistent expansion may lead to diffuse and nodular sclerosis.

Normal tuft

Expanded mesangium

Schematic of a glomerular tuft — not a histologic image

Slide 27 · PAS staining highlights the excess matrix

MORPHOLOGY

The excess diabetic mesangial matrix is PAS-positive.

PAS accentuates basement membranes and supports assessment of mesangial expansion.

Interpret an actual stain by identifying the pattern and location of matrix deposition.

PAS staining emphasizes carbohydrate-rich matrix

PAS-positive matrix

Mesangial expansion

Basement membranes

Conceptual stain targets, not microscopy

Slide 28 · Diffuse mesangial sclerosis is widespread

MORPHOLOGY

The lesion is defined by a diffuse increase in mesangial matrix.

Matrix deposition need not form discrete nodules.

Diffuse mesangial sclerosis can be present in glomeruli without nodules.

Widespread matrix

Residual capillary loops

Schematic of a glomerular tuft — not a histologic image

Slide 29 · Mesangial expansion correlates with proteinuria

MORPHOLOGY

Progressive expansion of the mesangium accompanies deterioration in renal function.

The source specifically notes correlation with increasing proteinuria.

This links a structural lesion to the principal clinical marker of nephropathy.

Mesangial matrix expansion

Tuft remodeling

Greater proteinuria

Conceptual sequence — schematic

Slide 30 · Nodular sclerosis develops within diffuse disease

MORPHOLOGY

Mesangial deposits can progressively develop a nodular configuration.

The classic nodular lesion does not replace all diffuse changes.

Adjacent lobules or glomeruli may remain diffusely sclerotic.

Diffuse pattern

Broad mesangial expansion

Nodular pattern

Discrete matrix nodules

Teaching comparison — schematic

Slide 31 · Kimmelstiel–Wilson nodules are distinctive

MORPHOLOGY

Nodular glomerulosclerosis is also termed intercapillary glomerulosclerosis.

Round or ovoid, often laminated nodules are PAS-positive.

The nodules consist of mesangial matrix rather than a proliferating cellular mass.

PAS-positive nodules

Mesangial matrix

Schematic of a glomerular tuft — not a histologic image

Slide 32 · The nodules occupy the mesangial lobules

MORPHOLOGY

Nodules develop in the mesangial core at the glomerular periphery.

Patent capillary loops may outline the nodules.

Other loops can become markedly dilated.

Mesangial core nodule

Peripheral capillary loop

Schematic of a glomerular tuft — not a histologic image

Slide 33 · Mesangiolysis weakens capillary anchoring

MORPHOLOGY

Mesangiolysis denotes disruption of support between capillaries and mesangial stalks.

Mesangiolytic features in nodular lesions.

Loss of structural support can permit localized dilation of capillary loops.

Mesangial support disrupted

Capillary anchoring lost

Loop dilation

Conceptual sequence — schematic

Slide 34 · Capillary microaneurysms may result

MORPHOLOGY

Localized capillary loop dilation reflects weakened mesangial support.

Microaneurysms may accompany nodular glomerulosclerosis.

They are a distinct feature from the extracellular matrix nodule itself.

Nodule

Excess mesangial matrix

Microaneurysm

Dilated capillary loop

Teaching comparison — schematic

Slide 35 · Nodules coexist with diffuse mesangial lesions

MORPHOLOGY

Nodules may involve only selected lobules within a glomerulus.

Apparently uninvolved lobules can still show diffuse mesangial sclerosis.

Evaluate the entire glomerular tuft rather than one isolated nodule.

Nodular lobule

Diffuse background

Schematic of a glomerular tuft — not a histologic image

Slide 36 · Fibrin caps are glomerular hyaline deposits

MORPHOLOGY

Hyaline accumulations in glomerular capillary loops.

These deposits are traditionally called “fibrin caps.”

They are associated findings rather than the definition of nodular sclerosis.

Capillary-loop hyaline

Nodular sclerosis

Schematic of a glomerular tuft — not a histologic image

Slide 37 · Capsular drops occur along Bowman capsule

MORPHOLOGY

Hyaline deposits may adhere to Bowman capsule.

These lesions are called “capsular drops.”

Distinguish the capsular location from capillary-loop fibrin caps.

Fibrin cap

Capillary-loop deposit

Capsular drop

Bowman capsule deposit

Teaching comparison — schematic

Slide 38 · Diffuse and nodular patterns: A comparison

MORPHOLOGY

Both patterns are characterized by excess mesangial matrix.

Nodular disease creates discrete spherical or ovoid PAS-positive deposits.

Diffuse background sclerosis persists even when characteristic nodules appear.

Feature

Diffuse mesangial sclerosis

Nodular glomerulosclerosis

Architecture

Widespread mesangial expansion

Discrete mesangial nodules

PAS

Matrix-positive

Strongly matrix-positive nodules

Background

May be present alone

Usually diffuse changes elsewhere

Support

Tuft remodeled

May show mesangiolysis

Slide 39 · Renal atherosclerosis adds ischemic injury

VASCULAR INJURY

Diabetes accelerates disease in large- and medium-sized renal arteries.

Renal macrovascular narrowing adds to glomerular and arteriolar damage.

Ischemia is therefore multifactorial in advanced diabetic kidneys.

Renal atherosclerosis

Reduced blood supply

Ischemic tissue injury

Conceptual sequence — schematic

Slide 40 · Hyaline arteriolosclerosis involves both poles

VASCULAR INJURY

Afferent arterioles may show hyaline thickening and narrowing.

Efferent arterioles are also affected in diabetic nephropathy.

This combined involvement is a useful morphologic clue.

Afferent arteriole

Efferent arteriole

Hyaline wall thickening with luminal narrowing — schematic

Slide 41 · Efferent arteriolar hyalinosis is informative

VASCULAR INJURY

That efferent arteriolar hyalinosis is rare without diabetes.

Assess arteriolar walls along with the glomerular matrix lesions.

No single arteriolar change substitutes for the overall morphologic pattern.

Afferent: Hyaline wall

Efferent: Hyaline wall

Hyaline wall thickening with luminal narrowing — schematic

Slide 42 · Glomerular and vascular lesions compound ischemia

VASCULAR INJURY

Mesangial sclerosis compromises glomerular architecture.

Hyaline arteriolosclerosis reduces microvascular caliber.

Their combined effects promote chronic tubulointerstitial injury.

Glomerulosclerosis

Arteriolosclerosis

Chronic ischemia

Tubulointerstitial injury

Convergent pathology / interacting components

Slide 43 · Chronic ischemia produces tubular atrophy

VASCULAR INJURY

Ischemic injury leads to loss and shrinkage of functional tubules.

Tubular atrophy accompanies interstitial fibrosis.

These changes are part of advanced diabetic kidney scarring.

Chronic ischemia

Tubular atrophy

Interstitial fibrosis

Conceptual sequence — schematic

Slide 44 · The advanced kidney may become contracted

VASCULAR INJURY

With long-standing disease, sclerosis and ischemia can reduce kidney size.

Granular surface change and marked cortical thinning.

Irregular depressions may reflect superimposed pyelonephritic scars.

Cortical scarring

Tubular atrophy

Interstitial fibrosis

Anatomic consequences — conceptual; Not gross specimen

Slide 45 · Pyelonephritis is more severe with diabetes

INFECTION

Acute and chronic pyelonephritis occur more commonly in diabetes.

The source describes greater severity in affected patients.

Pyelonephritis begins in the interstitium and can extend into tubules.

Interstitial infection

Tubular involvement

Additional renal damage

Conceptual sequence — schematic

Slide 46 · Papillary necrosis is a notable complication

INFECTION

Papillary necrosis is a necrotizing pattern of acute pyelonephritis.

It is more prevalent in people with diabetes than in those without diabetes.

This complication is separate from the characteristic glomerular sclerosing lesion.

Glomerular injury

Chronic matrix / microvascular lesions

Papillary necrosis

Necrotizing inflammatory complication

Teaching comparison — schematic

Slide 47 · The characteristic tissue pattern is composite

INTEGRATION

Glomerular: Thick GBM, diffuse matrix expansion, sometimes nodules.

Vascular: Afferent and efferent hyalinosis with renal atherosclerosis.

Chronic parenchymal: Tubular atrophy and interstitial fibrosis.

Glomerular sclerosis

Vascular hyalinosis

Tubulointerstitial scarring

Distinct but coexisting renal lesions

Slide 48 · Albuminuria is an early clinical manifestation

CLINICAL COURSE

Low-level urinary albumin excretion is an early signal of diabetic nephropathy.

The traditional term “microalbuminuria” is replaced by “moderately increased albuminuria.”

It is possible to have structural renal injury before symptomatic kidney disease.

Early microvascular injury

Moderately increased albuminuria

Clinical recognition

Conceptual sequence — schematic

Slide 49 · Albuminuria terminology defines severity

CLINICAL COURSE

The textbook defines moderately increased albuminuria as >30 and <300 mg/day.

Severely increased albuminuria is described at >300 mg/day.

These refer to daily urinary albumin excretion—not a spot urine ratio.

Textbook term

Daily urinary albumin

Former term

Moderately increased

>30 to <300 mg/day

Microalbuminuria

Severely increased

>300 mg/day

Macroalbuminuria

Slide 50 · Progression may lead to overt proteinuria

CLINICAL COURSE

Progressive renal injury increases albumin excretion.

Transition from low-grade albuminuria to overt nephropathy.

Hypertension commonly accompanies the more advanced proteinuric phase.

Early albuminuria

Increasing proteinuria

Advanced kidney disease

Conceptual sequence — schematic

Slide 51 · Proteinuria links clinic and morphology

CLINICAL COURSE

A clinical increase in proteinuria often reflects increasing mesangial matrix deposition.

In advanced disease, glomerular and vascular abnormalities coexist.

Interpret urine findings alongside renal function and systemic diabetic disease.

Matrix expansion

Protein permeability / proteinuria

Renal dysfunction

Conceptual sequence — schematic

Slide 52 · Hypertension compounds renal vulnerability

CLINICAL COURSE

Hypertension frequently accompanies overt diabetic nephropathy.

It can coexist with renal arteriolar hyalinosis and glomerulosclerosis.

The clinical phenotype reflects vascular as well as glomerular injury.

Albuminuria

Hypertension

Vascular pathology

Renal impairment

Convergent pathology / interacting components

Slide 53 · The clinical spectrum is broad

CLINICAL COURSE

Early nephropathy may be clinically silent except for urine albumin abnormalities.

Increasing proteinuria may precede marked loss of kidney function.

Advanced disease may require dialysis or renal transplantation.

Asymptomatic albuminuria

Proteinuric nephropathy

Advanced kidney failure

Conceptual sequence — schematic

Slide 54 · Not all patients progress identically

CLINICAL COURSE

The source places clinical evidence of nephropathy in roughly 30–40% of patients with diabetes.

Course differs among individuals with type 1 and type 2 diabetes.

Duration, glycemic exposure, and other risk factors influence progression.

Type 1 diabetes

Characteristic glomerular changes

Type 2 diabetes

Characteristic glomerular changes

Teaching comparison — schematic

Slide 55 · Chronic complications are often delayed

CLINICAL COURSE

Long-term complications typically accumulate after years of hyperglycemia.

The source describes many clinical complications first appearing after 15–20 years.

Timing is variable; Morphologic alterations can precede overt functional impairment.

Prolonged hyperglycemia

Structural lesions

Clinical manifestations

Conceptual sequence — schematic

Slide 56 · Loss of filtration becomes the final consequence

CLINICAL COURSE

Glomerulosclerosis reduces effective filtration surface.

Vascular narrowing and fibrosis reduce viable renal parenchyma.

The combined lesions may culminate in end-stage kidney disease.

Glomerular scarring

Ischemic parenchymal loss

Interstitial fibrosis

Kidney failure

Convergent pathology / interacting components

Slide 57 · Renal and cardiovascular injuries coexist

CLINICAL COURSE

Diabetes produces both macrovascular and microvascular disease.

Renal atherosclerosis and glomerular injury can occur in the same patient.

Kidney findings should be understood within the systemic vascular burden.

Macrovascular damage

Atherosclerotic ischemia

Microvascular damage

Glomerular microangiopathy

Teaching comparison — schematic

Slide 58 · Clinicopathologic patterns can be aligned

SYNTHESIS

Albuminuria: Abnormal filtration barrier and progressive glomerular matrix disease.

Falling filtration: Global nephron loss, vascular narrowing, and interstitial fibrosis.

Febrile infection or papillary necrosis: Consider a superimposed inflammatory lesion.

Clinical pattern

Pathologic correlate

Albuminuria

GBM / mesangial matrix injury

Progressive kidney failure

Sclerosis + ischemia + fibrosis

Acute renal infection

Pyelonephritis ± papillary necrosis

Slide 59 · Clinical case: Early nephropathy

APPLICATION

A patient with long-standing diabetes has no renal symptoms but increasing low-level urinary albumin excretion.

Which microscopic compartment is affected before overt kidney failure?

Explain why basement membrane thickening does not prevent protein leakage.

Assess

GBM and mesangium

Reason

Microangiopathy and permeability

Slide 60 · Clinical case: Nodular glomerular lesion

APPLICATION

A renal biopsy in a patient with long-standing diabetes shows PAS-positive round matrix nodules within glomerular lobules.

Name the characteristic nodular lesion.

What additional changes should be sought in the background tufts and arterioles?

Assess

Nodular mesangial sclerosis

Seek

Diffuse sclerosis + arteriolar hyalinosis

Slide 61 · Clinical case: Worsening kidney function

APPLICATION

A patient with diabetes develops rising proteinuria, hypertension, and declining filtration.

Connect glomerulosclerosis to vascular compromise and interstitial fibrosis.

Why can kidney size decrease in advanced disease?

Glomerular matrix

Vascular hyalinosis

Chronic ischemia

Atrophy and fibrosis

Slide 62 · Morphology exercise: Separate two deposits

APPLICATION

A PAS-stained diabetic glomerulus shows hyaline material within capillary loops and along Bowman capsule.

Identify the conventional name of each deposit by location.

Distinguish both from the mesangial Kimmelstiel–Wilson nodule.

Capillary loops

Fibrin caps

Bowman capsule

Capsular drops

Slide 63 · Four morphologic features worth recognizing

SYNTHESIS

Thickened glomerular capillary and tubular basement membranes.

Diffuse mesangial sclerosis with or without Kimmelstiel–Wilson nodules.

Hyaline arteriolosclerosis, including efferent arterioles.

Tubular atrophy and interstitial fibrosis in advanced disease.

Basement membranes

Mesangial matrix

Arterioles

Tubulointerstitium

Each contributes a different mechanistic or structural component

Slide 64 · One causal chain integrates the lecture

SYNTHESIS

Chronic metabolic abnormalities damage endothelium and alter matrix production.

Glomerular sclerosis and microvascular narrowing amplify renal damage.

Albuminuria precedes or accompanies progressive functional decline.

Chronic hyperglycemia

Matrix / vascular lesions

Albuminuria → renal decline

Conceptual sequence — schematic

Slide 65 · References and source boundaries

SELECTED SOURCES

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. Chapter 20: The Kidney (p. 841).

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. Chapter 24: The Endocrine System (diabetic chronic complications).

Source sections: chronic diabetic complications, microangiopathy, diabetic nephropathy, and clinical manifestations.