Typical Epidemic Classic Diarrhea Positive Hemolytic Uremic Syndrome

Slide 1 · Typical hemolytic uremic syndrome

Shiga toxin–associated thrombotic microangiopathy

Etiology · endothelial injury · renal morphology · clinical consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Relate typical HUS to the broader family of thrombotic microangiopathies.

Trace the proposed link from intestinal Shiga toxin exposure to endothelial injury and microthrombi.

Interpret shared renal morphology and the clinical pattern of hemolysis, thrombocytopenia, and renal dysfunction.

Distinguish typical HUS from complement-mediated HUS and thrombotic thrombocytopenic purpura.

Slide 3 · Thrombotic microangiopathy defines the parent lesion

Thrombotic microangiopathy (TMA) is a group of syndromes with thrombi in capillaries and/or arterioles.

The thrombi compromise perfusion and produce tissue ischemia and organ dysfunction.

Hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are major examples.

Slide 4 · The microvessel is the decisive anatomic site

Schematic: Microvascular lumen

Occluding platelet thrombus

Capillary and arteriolar lumens may be narrowed or occluded by thrombi.

Passing erythrocytes encounter increased mechanical stress.

Microvascular obstruction links blood abnormalities to organ injury.

Slide 5 · A single vascular process generates three consequences

Erythrocyte injury

Microangiopathic hemolytic anemia

Platelet consumption

Thrombocytopenia

Vascular occlusion

Renal ischemia and dysfunction

Slide 6 · Typical HUS is a cause-defined member of TMA

Typical HUS

Shiga toxin–associated enteric infection

Endothelial injury appears to initiate TMA

Renal involvement is prominent

Other major TMAs

Complement-mediated HUS: Dysregulated complement

TTP: Deficient ADAMTS13 activity

Microscopic thrombi overlap across categories

Slide 7 · What do “typical,” “epidemic,” and “diarrhea-positive” denote?

These historical names refer to the classic enteric-infection–associated HUS syndrome.

The preferred causal framing is Shiga toxin–mediated HUS.

Clinical labels describe an association; They do not identify a unique histologic lesion.

Slide 8 · TMA classification follows the initiating disturbance

Syndrome

Principal trigger

Mechanistic emphasis

Typical HUS

Shiga toxin–producing infection

Endothelial injury

Complement-mediated HUS

Complement dysregulation

Endothelial injury

TTP

ADAMTS13 deficiency

Platelet activation

Slide 9 · TMA phenotypes overlap more than the labels suggest

HUS and TTP share microangiopathic anemia, platelet consumption, and tissue injury.

Neurologic symptoms may occur in HUS; Not every patient with TTP exhibits its classic pentad.

A causal classification is more discriminating than the clinical triad alone.

Slide 10 · Why the kidney is a major target in HUS

Renal capillary / arteriole

Small-vessel microthrombi

Hypoperfusion

Glomerular and cortical ischemia

Tissue injury

Reduced renal function

The renal manifestations reflect microvascular ischemic injury.

Slide 11 · Red cell fragmentation is mechanical, not marrow failure

Schematic: Microvascular lumen

Fragmentation under shear

Thrombi and narrowed lumens impose shear stress on circulating erythrocytes.

Erythrocytes fragment within the circulation.

The consequence is a microangiopathic hemolytic anemia.

Slide 12 · Thrombocytopenia reflects platelet consumption

Platelet activation

Platelets enter microthrombi

Microvascular deposition

Circulating platelets are consumed

Blood count

Thrombocytopenia emerges

Slide 13 · Renal dysfunction is a consequence of vascular occlusion

Glomerular capillaries and intrarenal arterioles may become thrombosed.

Loss of perfused microvascular surface impairs function.

Severe, extensive ischemia may progress to cortical necrosis.

Slide 14 · Typical HUS commonly follows enteric infection

Contaminated food

Exposure to toxin-producing organisms

Intestinal infection

Inflammation of gastrointestinal mucosa

Toxin exposure

Circulating Shiga-like toxin

Renal TMA

Endothelial injury and thrombosis

Slide 15 · Shiga toxin–producing Escherichia coli is central

Most classic HUS cases follow intestinal infection with Shiga-like toxin–producing E. Coli.

The bacterial toxin, rather than a primary ADAMTS13 defect, anchors the etiologic explanation.

The organism–toxin association defines the classical acquired form.

Slide 16 · E. Coli O157:H7 is the textbook’s leading example

The most commonly implicated strain named is E. Coli O157:H7.

The serotype is an illustrative frequent cause, not the definition of all Shiga toxin–mediated HUS.

Etiologic thinking should begin with the toxin-producing infection.

Slide 17 · Why “Shiga-like toxin” is the textbook term

The toxins produced by the implicated E. Coli strains resemble Shiga toxin.

The name refers to the toxin made by Shigella dysenteriae.

The shared toxin mechanism explains why more than one organism may trigger this TMA pattern.

Slide 18 · Shigella dysenteriae is a less common association

Common association

Shiga toxin–producing E. Coli

O157:H7 highlighted in the text

Intestinal infection preceding HUS

Less common association

Shigella dysenteriae

A similar toxin-associated syndrome

Different microorganism; Convergent endothelial injury

Slide 19 · The intestine is the entry point for circulating toxin

Enteric infection

Inflamed intestinal mucosa

Absorption

Toxin enters circulation

Systemic exposure

Microvascular endothelium affected

Clinical HUS

TMA appears after gastrointestinal illness

Slide 20 · Bloody diarrhea often precedes the renal syndrome

The Chapter 14 account describes bloody diarrhea during the gastrointestinal illness.

HUS typically emerges a few days after this enteric phase.

The temporal sequence is an important diagnostic clue, not a unique pathognomonic sign.

Slide 21 · Children and older adults are described as higher-risk

Children and older adults as groups at greatest risk for infection-associated HUS.

The epidemiologic context can strengthen suspicion after an enteric illness.

Age does not replace etiologic or hematologic evaluation.

Slide 22 · The precise molecular pathogenesis remains incompletely resolved

How Shiga-like toxin causes HUS is not fully understood.

The endothelial activation model is presented as one proposed explanation.

A Factor H–complement link is discussed as an additional possibility.

Slide 23 · Endothelial injury is the initiating emphasis in HUS

Shiga-like toxin

Potential endothelial activation/injury

Prothrombotic endothelium

Platelet activation

Microthrombi

Capillary and arteriolar occlusion

This is the dominant pathophysiologic model, not a fully settled molecular sequence.

Slide 24 · Leukocyte adhesion molecules increase in one model

Toxin-exposed endothelial cells are proposed to increase adhesion-molecule expression.

The change denotes a more activated endothelial phenotype.

This response is one component of a wider injury state linked to thrombosis.

Slide 25 · Endothelin expression contributes to vasoconstriction

Toxin-associated endothelial change

Endothelin expression rises

Vascular smooth muscle

Greater vasoconstrictor influence

Microcirculation

Potentially reduced blood flow

Endothelin induction is proposed in the Robbins mechanistic model.

Slide 26 · Reduced nitric oxide removes a vasodilatory influence

Endothelial activation

Nitric oxide production falls

Vascular response

Reduced vasodilatory signaling

Net effect

Favoring vasoconstriction

Slide 27 · Vascular tone and thrombosis amplify ischemia

Vasoconstriction

Endothelin increased

Nitric oxide reduced

Further restricts blood flow

Microthrombi

Endothelial injury activates platelets

Aggregates narrow or occlude vessels

Ischemic consequences converge

Slide 28 · TNF is a conditional cofactor for endothelial apoptosis

That cytokines such as tumor necrosis factor (TNF) may modify toxin responses.

In their presence, Shiga-like toxin may induce endothelial apoptosis.

This interaction is hypothesis-dependent; It is not an obligatory step in every case.

Slide 29 · Endothelial apoptosis is one proposed lesion mechanism

Shiga-like toxin

Exposure of endothelium

Inflammatory cytokine context

Potentially enhances injury

Endothelial apoptosis

Prothrombotic microvascular surface

Apoptosis is a conditional mechanism’s model.

Slide 30 · Endothelial injury provides a substrate for platelet activation

Schematic: Microvascular lumen

Occluding platelet thrombus

Activated or damaged endothelium changes the local vascular environment.

Platelet activation and aggregation are favored.

The resulting occlusive lesions constitute thrombotic microangiopathy.

Slide 31 · Platelet microthrombi connect toxin exposure to organ injury

Toxin-associated injury

Endothelial activation

Platelet response

Microvascular thrombi

Mechanical effect

Red cell fragmentation

Perfusion effect

Renal ischemia

Slide 32 · The renal glomerulus is a microvascular target

Schematic glomerular capillary bundle

Thrombi within loops

Glomerular capillary loops may contain thrombi.

Occluded lumens disturb local flow and filtration.

TMA morphology is not exclusive to Shiga toxin–mediated HUS.

Slide 33 · Intrarenal small vessels are also involved

Schematic: Microvascular lumen

Occluding platelet thrombus

Interlobular arteries and arterioles may contain occlusive thrombi.

Capillary and arteriolar lesions can coexist.

Widespread involvement increases the risk of ischemic damage.

Slide 34 · An integrated proposed pathogenesis

Enteric infection

Shiga-like toxin

Endothelial response

Activation ± apoptosis

Hemodynamic change

↑ endothelin · ↓ nitric oxide

Platelet thrombosis

Occlusive microthrombi

TMA phenotype

Hemolysis · ↓ platelets · renal injury

Slide 35 · Factor H offers a possible complementary mechanism

Proposed mechanism · not definitive

Complement activation

Endothelial injury

Factor H regulation

Restrains

A proposed toxin–Factor H interaction could impair complement regulation.

Reduced regulation might permit excessive complement activation.

This link as intriguing evidence, not an established universal pathway.

Slide 36 · Factor H normally restrains alternative-pathway activity

Factor H

Regulatory complement protein

Alternative-pathway C3 convertase

Promotes its breakdown

Cell surfaces

Protected against uncontrolled complement activation

Slide 37 · Do not equate a toxin hypothesis with inherited HUS

Typical HUS

Shiga-like toxin exposure is the usual initiating insult

Factor H interference is a proposed contribution

A preceding intestinal infection is characteristic

Complement-mediated HUS

Primary dysregulation of complement regulation

Mutations or regulatory autoantibodies described

Triggers and course differ by etiology

Slide 38 · HUS and TTP start from different dominant events

HUS: Endothelium first

Toxin or complement disturbance

Endothelial injury / activation

Secondary platelet activation

TTP: Platelets first

ADAMTS13 function deficient

Ultra-large vWF multimers persist

Platelet activation initiates microthrombi

Slide 39 · Schistocytes reflect shear across damaged microvessels

Schematic red-cell forms — not a blood film

Fragmented erythrocytes

Luminal narrowing imposes mechanical stress on erythrocytes.

Fragmented red cells may appear as schistocytes or helmet-shaped forms.

Morphology supports microangiopathic hemolysis, but does not establish its cause.

Slide 40 · Microangiopathic anemia is a shared TMA manifestation

TTP and HUS both develop intravascular mechanical hemolysis.

The anemia is downstream of microvascular thrombi and altered flow.

Hemolysis alone cannot distinguish infectious HUS from other thrombotic microangiopathies.

Slide 41 · PT and PTT are usually normal in TTP and HUS

TMA (HUS/TTP)

Platelet-rich microvascular thrombi

Coagulation cascade not the primary initiating mechanism

PT and PTT usually normal

DIC

Pathogenetically distinct process

Activation of coagulation is central

Some findings, including hemolysis, overlap

Slide 42 · Acute renal TMA may cause cortical necrosis

Schematic renal cortical ischemia

Ischemic cortical region

Kidneys may exhibit patchy or diffuse cortical necrosis.

Subcapsular petechiae may accompany acute injury.

Severe perfusion disturbance can produce sharply cortex-limited infarction.

Slide 43 · Glomerular thrombi distend and obstruct capillary loops

Schematic glomerular capillary bundle

Thrombi within loops

Glomerular capillaries are described as distended by thrombi.

Occlusion interrupts local perfusion.

This morphologic pattern is shared by different HUS/TTP etiologies.

Slide 44 · Mesangial matrix and cells may be damaged

Active renal TMA can disrupt mesangial matrix.

Damage to mesangial cells may culminate in mesangial destruction.

These lesions accompany capillary thrombosis in the shared morphology account.

Slide 45 · Interlobular arterial and arteriolar thrombi

Schematic: Microvascular lumen

Occluding platelet thrombus

Small arterial lumens may be obstructed by thrombi.

Vessel occlusion contributes to cortical ischemia.

The anatomic distribution explains why diffuse injury can follow small-vessel disease.

Slide 46 · Extensive ischemia can produce cortical infarction

Schematic renal cortical ischemia

Ischemic cortical region

When severe, the ischemic process may be sharply confined to the cortex.

Histology may show coagulative necrosis with relatively preserved adjacent areas.

A large ischemic territory can manifest clinically as renal failure.

Slide 47 · Repeated endothelial damage leaves chronic vascular scars

The shared HUS/TTP morphology varies with disease chronicity.

Persistent or prior microvascular injury may leave cortical scarring.

Chronic features are particularly emphasized in the atypical HUS section; They are not diagnostic of infection-associated HUS.

Slide 48 · Double contours reflect chronic capillary-wall remodeling

Acute lesion

Capillary distension

Microthrombotic occlusion

Mesangial injury

Chronic remodeling

Shrunken glomeruli

Basement-membrane duplication

Double contours / “tram tracks”

Slide 49 · Arterial remodeling may perpetuate hypoperfusion

Chronically injured arteries may accumulate extra cell and connective-tissue layers.

The resultant wall thickening narrows the lumen.

Arteriolar hyalinosis may become prominent when chronic features predominate.

Slide 50 · Renal TMA morphology does not specify its trigger

Shared pathologic observation

What it supports

What it cannot prove

Glomerular thrombi

Active microvascular thrombosis

Shiga toxin etiology

Mesangial injury

Microvascular tissue damage

Specific HUS subgroup

Double contours

Chronic endothelial injury

Unique infectious cause

Slide 51 · Renal-predominant HUS and neurologic-predominant TTP

HUS pattern

Renal failure often prominent

Hemolytic anemia and thrombocytopenia

Some patients still develop neurologic symptoms

TTP pattern

Neurologic involvement classically prominent

Severe renal injury less common

The clinical spectra overlap

Slide 52 · ADAMTS13 distinguishes TTP mechanism from HUS

Functional ADAMTS13

Cleaves large vWF multimers

Deficient activity in TTP

Abnormally large vWF multimers

Platelet activation

Small-vessel aggregation

The Chapter 14 source describes normal ADAMTS13 levels in HUS.

Slide 53 · Toxin history and complement dysregulation are different clues

Clinical–causal clue

Typical HUS

Complement-mediated HUS

Trigger

Enteric toxin-producing infection

Inherited/acquired regulation defect

Initiating emphasis

Endothelial toxin injury

Complement-mediated endothelial injury

Course

Recovery often occurs after acute episode

May recur or persist

Slide 54 · The diagnosis should integrate cause, blood and organ findings

Causal setting

Recent enteric illness / Shiga toxin association

Hematologic syndrome

Hemolysis + platelet consumption

Organ injury

Acute renal dysfunction / ischemic TMA

Slide 55 · Do not assign “typical HUS” from a renal biopsy alone

Active HUS and TTP lesions may be morphologically indistinguishable.

Biopsy establishes microvascular injury and its chronicity, not the precise causal trigger.

The infectious context and the broader hematologic differential remain essential.

Slide 56 · DIC can mimic the hemolytic microvascular pattern

DIC and TMA can both produce microvascular occlusion and red cell fragmentation.

Unlike HUS and TTP, coagulation-cascade activation is central to DIC.

Interpret the coagulation profile within the full clinical context.

Slide 57 · Renal recovery commonly occurs over weeks in milder disease

That most patients with less severe renal failure recover renal function within weeks.

This describes an acute recovery pattern, not assurance of lifelong renal normality.

The extent of initial renal damage influences later risk.

Slide 58 · Greater initial renal injury changes the prognosis

Less severe renal failure

Recovery often within weeks

Underlying renal damage

Possible residual injury

Long-term perspective

Some patients retain impaired renal function

Slide 59 · Long-term renal risk persists despite acute improvement

The chapter cautions that 15–25-year renal outcomes are less reassuring than short-term recovery.

Residual structural injury may remain clinically relevant after the infection resolves.

Follow-up cannot be replaced by the observation that acute renal function improved.

Slide 60 · A quoted follow-up study is a cohort, not a prevalence

Normal renal function in 10 of 25 patients with prior typical HUS at long-term assessment.

10

Normal renal function

15

Not normal renal function

One historical cohort (n = 25); Not a population-level probability or prediction.

Slide 61 · Supportive care is the textbook’s treatment emphasis

Chapter 14 describes infection-associated HUS as managed supportively.

Some survivors have permanent kidney damage and may require renal replacement therapy.

Specific modern testing or treatment algorithms are outside the source-defined scope of this lecture.

Slide 62 · Case: Renal failure after bloody diarrheal illness

A child has a bloody diarrheal illness, followed several days later by anemia, thrombocytopenia, and acute renal dysfunction.

Which initiating association best explains this pattern?

Shiga toxin–producing enteric infection causing typical HUS; The evidence is a constructed teaching vignette, not a patient record.

Slide 63 · Case: Identical biopsy, different etiologic mechanism

Two patients show glomerular capillary thrombi and mesangial damage. One had preceding enteritis; The other has a defect in complement regulation.

Can the shared renal microscopic changes identify which patient has typical HUS?

No. HUS/TTP forms share a TMA morphologic pattern; Causal context is required to type the syndrome.

Slide 64 · Case: Neurologic deficits do not automatically exclude HUS

A patient with microangiopathic hemolysis, thrombocytopenia and kidney injury also develops neurologic symptoms.

Does neurologic dysfunction alone establish TTP?

No. The source explicitly notes overlap and neurologic findings in some patients with HUS.

Slide 65 · Clinical synthesis: Trace cause to consequence

Cause

Shiga toxin enteric illness

Primary process

Endothelial injury / activation

Microvascular lesion

Platelet-rich thrombosis

Blood effects

Schistocytes + thrombocytopenia

Kidney effects

Ischemia / renal impairment

Slide 66 · Five conclusions to retain

Typical HUS is a Shiga toxin–associated thrombotic microangiopathy.

Endothelial injury, platelet activation, and microvascular obstruction explain its renal and blood manifestations.

The precise toxin-to-TMA mechanism remains incompletely understood.

Morphologic TMA does not identify its specific etiology.

Acute renal recovery does not exclude important long-term consequences.

Slide 67 · Textbook sources and interpretive boundaries

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th ed. 2026. Chapter 20, “The Kidney,” pp. 853–855.

Same textbook, Chapter 14, “Red Blood Cell and Bleeding Disorders,” pp. 605–606 and section on red cell trauma.

Source text was supplied in Markdown; original chapter-page images were not available for direct verification.

Vascular, blood-smear, and renal figures in this deck are original editable schematics, not clinical specimens.