Acute Eczematous Dermatitis

Slide 1 · Acute Eczematous Dermatitis

A clinicopathologic lecture

From antigen exposure to spongiotic inflammation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Classify major initiating contexts for eczematous dermatitis

Trace allergic contact sensitization and re-exposure

Explain epidermal spongiosis and vesicle formation

Connect lesion evolution with histopathology and management

Slide 3 · Eczema is a clinicopathologic reaction pattern

Acute eczematous dermatitis is among the common inflammatory skin disorders

“Eczema” describes an acute papulovesicular, often weeping presentation

Multiple distinct initiating factors can converge on spongiotic epidermal injury

Slide 4 · The phase of disease changes the phenotype

Acute: Erythema, edema, papulovesicles, oozing and crusts

Persistent lesions: Reactive epidermal thickening and increased scale

A single eruption may exhibit features of more than one phase

Acute eruption

Exudation / vesicles

Persistent inflammation

Scaling plaque

Schematic

Slide 5 · Spongiosis defines the acute tissue response

Spongiosis means edema within intercellular spaces of epidermis

Fluid separates keratinocytes, particularly in the stratum spinosum

Progressive spongiosis can culminate in intraepidermal vesicles

EPIDERMAL INTERCELLULAR EDEMA

Fluid widens spaces

Schematic

Slide 6 · The epidermis and dermis play different roles

Epidermis: Keratinocytes, desmosomes and intraepidermal dendritic cells

Papillary dermis: Vessels and sites of early inflammation and edema

Eczematous inflammation links dermal recruitment to epidermal change

EPIDERMIS

Superficial dermis

Langerhans cell

Schematic

Slide 7 · Keratinocyte adhesion normally resists separation

Desmosomes connect adjacent keratinocytes and help maintain skin integrity

Keratin forms a durable barrier in the epidermis

Interstitial epidermal fluid mechanically widens spaces between cells

KERATINOCYTE ATTACHMENT

Intercellular fluid expands gap

Connections resist separation

Schematic

Slide 8 · Langerhans cells connect skin to adaptive immunity

Intraepidermal Langerhans cells capture and process antigens

They migrate toward regional lymph nodes for T-cell presentation

This function is central to allergic contact sensitization

ANTIGEN PRESENTATION

Langerhans cell

T cell

Antigen display supports sensitization

Schematic

Slide 9 · Skin-homing T cells return to sites of antigen

Activated lymphocytes can express cutaneous lymphocyte-associated antigen (CLA)

Chemokine receptors aid localization to cutaneous inflammation

On re-exposure, memory T cells accumulate at the site of antigen

Lymph node activation

Circulating T cells

Skin-homing signals

Cutaneous inflammation

Schematic

Slide 10 · Five initiating contexts are recognized

Allergic contact dermatitis; Atopic dermatitis

Drug-related eczematous dermatitis; Photoeczematous dermatitis

Primary irritant dermatitis

INITIATING FACTORS

Allergic contact

Atopic

Drug-related

Photoeczematous

Primary irritant

Schematic

Slide 11 · External versus internal antigen exposure

“Outside”: Contact with a locally applied antigen, such as poison ivy

“Inside”: A circulating antigen associated with an ingested agent

This exposure distinction directs the clinical history; It does not determine histology by itself

INITIATING CONTEXT

LOCAL CONTACT

CIRCULATING EXPOSURE

Same reaction family; Different investigative routes

Schematic

Slide 12 · Allergic contact dermatitis: Acquired reactivity

A contact chemical can modify self proteins, producing a new antigenic target

Sensitization generates effector and memory T cells

Re-exposure elicits localized delayed inflammatory injury

Contact chemical

Hapten–protein neoantigen

T-cell sensitization

Re-exposure response

Schematic

Slide 13 · Primary irritant dermatitis is a distinct initiating category

Primary irritant dermatitis separately from allergic contact disease

An irritant history is not proof of hapten-specific memory T-cell sensitization

Interpret a spongiotic biopsy with the exposure pattern, not the label alone

Slide 14 · Atopic dermatitis enters the same morphologic spectrum

Atopic dermatitis is one of the classified eczematous disorders

Spongiosis and chronic epidermal reaction can occur across eczematous subtypes

Clinical context is necessary to separate atopic from contact-related eczema

Slide 15 · Some ingested drugs produce an eczematous eruption

The provoking agent may be circulating rather than applied directly

Biopsies from certain drug reactions may contain eosinophils

Drug exposure and chronology matter more than one histologic clue

INITIATING CONTEXT

EXPOSURE HISTORY

DERMAL INFILTRATE

Same reaction family; Different investigative routes

Schematic

Slide 16 · Photoeczematous dermatitis adds a light-related context

Photoeczematous dermatitis is a recognized initiating category

Ultraviolet exposure can affect antigen properties and epidermal immune cells

Assess the distribution and exposure history rather than assuming one mechanism

Slide 17 · A shared pattern does not imply identical pathogenesis

Identifiable

Not established by morphology alone

Epidermal intercellular edema

Exact environmental or systemic trigger

Papulovesicular eczema pattern

Specific antigen or sensitization status

Read as a diagnostic comparison, not as an exclusive criterion.

Slide 18 · Poison ivy demonstrates florid contact eczema

Urushiol from poison ivy/oak provides a classic contact antigen

Pruritic, edematous, oozing plaques may form after contact

Both vesicles and larger bullae can occur in a pronounced reaction

Slide 19 · Patterned distribution can reveal contact exposure

Nickel-associated dermatitis related to a necklace

The eruption follows a site of contact instead of requiring generalized disease

Distribution is a diagnostic clue and should be interpreted with timing and history

Slide 20 · Exposure site helps contextualize histology

Examine where the rash begins and whether it matches a plausible contact area

Distinguish direct exposure from ingestion and other initiating contexts

Combine site, time course and morphology to refine the differential

FROM PATTERN TO CAUSE

Spongiotic tissue reaction

Clinical morphology

Exposure chronology

Distribution / phase

Correlate before assigning a specific cause

Schematic

Slide 21 · Contact chemicals can behave as haptens

Small chemicals may react with endogenous skin proteins

The resulting altered proteins can function as neoantigens

This explains how a local exposure can become immunologically recognizable

Contact chemical

Binds self protein

Neoantigen

Adaptive recognition

Schematic

Slide 22 · Antigen capture occurs within the epidermis

Langerhans cells reside in the epidermis where exposure occurs

They internalize and process contact-associated neoantigens

Cutaneous antigen capture initiates a regional immune response

ANTIGEN PRESENTATION

Langerhans cell

T cell

Antigen display supports sensitization

Schematic

Slide 23 · Migration carries antigen to the lymph node

Antigen-bearing Langerhans cells enter dermal lymphatics

They reach draining regional lymph nodes

An encounter outside the epidermis is needed to establish T-cell sensitization

Epidermal uptake

Dermal lymphatics

Draining lymph node

T-cell encounter

Schematic

Slide 24 · Naive CD4 T cells are activated by presentation

Antigen presentation stimulates naive CD4 T lymphocytes

Activated cells differentiate into effector and memory populations

This creates capacity for a response on later exposure

Neoantigen display

Naive CD4 T cell

Activation

Effector + memory

Schematic

Slide 25 · Immunologic memory explains re-exposure responses

After initial sensitization, memory cells persist

Re-exposure engages a prepared cutaneous immune system

The episode can therefore be amplified relative to first contact

Sensitization

Memory T cells

Repeat exposure

Localized flare

Schematic

Slide 26 · Antigen re-exposure recruits memory T cells

Memory T cells recognizing antigen localize to involved skin

Skin-homing surface molecules help direct recruitment

Inflammatory mediators from these cells recruit other leukocytes

Re-exposure

Memory T-cell homing

Cytokine release

Inflammatory influx

Schematic

Slide 27 · CLA and chemokine receptors guide tissue localization

Cutaneous lymphocyte-associated antigen marks a skin-homing T-cell phenotype

Robbins also cites chemokine receptors CCR4 and CCR10 in the skin immune system

Homing signals provide spatial specificity to the inflammatory response

Slide 28 · Cytokines translate recognition into tissue injury

Recruited and resident T cells release cytokines and chemokines

These mediators attract additional inflammatory cells

Dermal inflammation and epidermal edema produce the visible eruption

CUTANEOUS IMMUNE RESPONSE

Memory T cell

Mediators

Inflammatory cells

Inflammatory recruitment → erythema, itch, spongiosis

Schematic

Slide 29 · Erythema and pruritus can develop within a day

The re-exposure response developing within approximately 24 hours

Erythema and itch mark the acute spongiotic phase

The exact clinical timeline must still be assessed in each patient

Contact re-exposure

Memory-cell response

Mediator release

Erythema + itch

Schematic

Slide 30 · Ultraviolet light has opposing immune effects

UV effect on cells

UV effect on antigen

Langerhans-cell injury

Altered antigen structure

Reduced sensitization capacity

Potentially increased sensitivity

Read as a diagnostic comparison, not as an exclusive criterion.

Slide 31 · IL-4 and IL-13 provide therapeutic context

Severe eczema to Th2-derived cytokines IL-4 and IL-13

Biologic agents blocking cytokine action can benefit severe disease

This treatment observation is not a universal diagnostic test for eczema subtype

Th2 cytokine signaling

Inflammation maintained

Cytokine blockade

Potential clinical response

Schematic

Slide 32 · The visible acute lesion is papulovesicular

An erythematous background accompanies small raised papules and vesicles

Lesions are often pruritic and may develop exudate

Crusting follows when exudate dries at the surface

Slide 33 · Pruritus, edema and oozing co-occur

Inflammation drives erythema and itch

Fluid accumulation expands the epidermal intercellular spaces

Surface rupture of vesicles produces an oozing clinical appearance

Dermal inflammation

Epidermal fluid

Vesicle / rupture

Oozing + crust

Schematic

Slide 34 · Vesicles and bullae express the same process

Fluid accumulation can coalesce into intraepidermal cavities

Small spaces become microvesicles, with larger blisters in florid eruptions

The size of a blister does not identify the initiating antigen

VESICLE WITHIN EPIDERMIS

Fluid-filled intraepidermal space

Schematic

Slide 35 · Crust can reflect dried exudate or infection

Acute eczema often has crusted papulovesicles

Secondary bacterial infection can produce yellow crust—impetiginization

A yellow crust requires clinical assessment rather than automatic attribution

Slide 36 · Excoriated, oozing skin is vulnerable to infection

Eczematous lesions can become secondarily infected

Superinfection changes the surface appearance and clinical priorities

Distinguish primary inflammation from a superimposed infectious component

Slide 37 · Long-standing eczema becomes less wet

Persistent lesions gradually lose prominent vesiculation and oozing

The surface becomes increasingly scaly and thickened

Morphologic chronicity may obscure the original acute mechanism

Spongiosis

Vesicle + ooze

Acanthosis

Hyperkeratosis + scale

Schematic

Slide 38 · Acanthosis is a reactive epidermal response

Acanthosis refers to increased thickness of the viable epidermis

It as lesions persist

It explains the raised plaque component of long-standing eczema

PERSISTENT EPIDERMAL RESPONSE

Thickened stratum corneum

Acanthosis: Increased viable epidermal thickness

Schematic

Slide 39 · Hyperkeratosis produces a drier, scaly surface

Hyperkeratosis means excess stratum corneum thickness

With chronicity, lesions become progressively hyperkeratotic

A thick scaly plaque can represent previously vesicular eczema

PERSISTENT EPIDERMAL RESPONSE

Thickened stratum corneum

Acanthosis: Increased viable epidermal thickness

Schematic

Slide 40 · Pigmentation can alter clinical recognition

Eczematous dermatitis with hyperpigmentation in darker skin

The appearance of erythema varies with skin pigmentation

Interpret the eruption through morphology, pruritus and exposure history, not redness alone

Slide 41 · Postinflammatory hypopigmentation may occur

The textbook also notes hypopigmentation after inflammation in darker skin

Pigment change can persist beyond the most active inflammatory lesion

Do not equate a pigmentary change with active vesiculation

Slide 42 · The histologic sequence begins in the dermis

Earliest lesions feature superficial perivascular lymphocytes

Papillary dermal edema and mast-cell degranulation accompany inflammation

Epidermal spongiosis then becomes conspicuous

EPIDERMIS

Superficial dermis

Langerhans cell

Schematic

Slide 43 · Papillary dermal edema precedes overt vesicles

Early inflammatory fluid increases in superficial dermal tissue

Dermal vascular and immune events occur before or with epidermal changes

A very early biopsy may show less developed epidermal spongiosis

Slide 44 · Spongiosis is intercellular—not intracellular—edema

Fluid collects between epidermal keratinocytes

Intercellular spaces expand while neighboring cells remain linked at points

The characteristic pattern is most apparent in the stratum spinosum

EPIDERMAL INTERCELLULAR EDEMA

Fluid widens spaces

Schematic

Slide 45 · Desmosomes are stressed as the spaces enlarge

Progressive fluid accumulation splays apart keratinocytes

Connections between cells may appear stretched or disrupted

Mechanical separation helps generate small epidermal cavities

KERATINOCYTE ATTACHMENT

Intercellular fluid expands gap

Connections resist separation

Schematic

Slide 46 · Intraepidermal microvesicles result from coalescence

Edema-induced epidermal spaces can merge

Focal detachment or shearing forms microvesicles within the epidermis

These microscopic cavities underlie clinical vesiculation

VESICLE WITHIN EPIDERMIS

Fluid-filled intraepidermal space

Schematic

Slide 47 · Histology changes along a continuous timeline

First: Superficial dermal edema and perivascular cells

Next (within 24–48 hours): Epidermal spongiosis and microvesicles

Later: Abnormal scale, acanthosis and hyperkeratosis

Dermal edema

Spongiosis

Microvesicles

Acanthosis + scale

Schematic

Slide 48 · Normal versus spongiotic epidermis

Normal: Densely apposed keratinocytes with narrow intercellular spaces

Spongiotic: Expanded spaces and residual intercellular links

Severe spongiosis can progress beyond separation to true vesicles

SIDE-BY-SIDE EPIDERMIS

Normal

Spongiotic

Schematic

Slide 49 · Certain drug eruptions suggest a deeper infiltrate

Histologic clue

Clinicopathologic question

Eosinophils with perivascular cells

Recent or ongoing drug exposure?

Superficial + deep involvement

Does chronology support the agent?

Read as a diagnostic comparison, not as an exclusive criterion.

Slide 50 · Contact eczema often favors superficial mononuclear cells

Contact-related eczema typically shows superficial mononuclear inflammation

This pattern with eosinophil-rich drug-associated reactions

Infiltrate distribution helps prioritize—but does not finalize—the etiology

Slide 51 · Inflammatory cells provide clues, not certainty

Histology can support

Histology alone cannot prove

Spongiosis and phase

Exact contact allergen

Infiltrate depth / composition

Drug causality

Degree of epidermal change

A unique eczema subtype

Read as a diagnostic comparison, not as an exclusive criterion.

Slide 52 · Urticaria favors dermal edema without spongiosis

Urticaria

Eczematous dermatitis

Dermal edema / wheals

Epidermal spongiosis

Epidermis generally normal

Papulovesicles and crusting

Mast-cell hyperpermeability

Often T-cell–linked inflammation

Read as a diagnostic comparison, not as an exclusive criterion.

Slide 53 · The distribution of edema separates two patterns

In urticaria, edema is concentrated in superficial dermis

In eczema, fluid also extends into the epidermis

This anatomical distinction explains wheals versus vesicles

LOCATION OF FLUID

Urticaria

Eczema

Dermis only

Epidermis involved

Schematic

Slide 54 · Interface injury is not spongiotic dermatitis

Eczematous pattern

Erythema multiforme pattern

Spongiosis ± microvesicles

Interface dermatitis

Intercellular epidermal fluid

Junctional keratinocyte injury

Eczematous eruption

Often targetoid lesions

Read as a diagnostic comparison, not as an exclusive criterion.

Slide 55 · A diagnosis begins with the eruption’s morphology

Are there papulovesicles, surface exudate, crusts or plaques?

Is the eruption acute, recurrent or persistent?

Is there a contact-pattern distribution or possible systemic exposure?

FROM PATTERN TO CAUSE

Spongiotic tissue reaction

Clinical morphology

Exposure chronology

Distribution / phase

Correlate before assigning a specific cause

Schematic

Slide 56 · Clinical history is essential for the etiologic label

Ask about locally applied substances and contact patterns

Review ingested medications or other circulating exposures

Assess relation to light exposure and the clinical setting of atopy

Slide 57 · The biopsy establishes pattern and activity

Document epidermal spongiosis, vesiculation and reactive thickening

Assess papillary dermal edema and the depth of inflammatory infiltrate

Interpret stage-dependent findings with the eruption and exposure history

FROM PATTERN TO CAUSE

Spongiotic tissue reaction

Clinical morphology

Exposure chronology

Distribution / phase

Correlate before assigning a specific cause

Schematic

Slide 58 · Clinicopathologic correlation prevents overcalling

“Spongiotic dermatitis” is a useful histologic description

The differential remains broad across the listed eczema contexts

A specific causal diagnosis needs corroborating clinical information

Slide 59 · Avoidance addresses the initiating factor

Treatment starts by identifying potentially removable offending substances

External or ingested exposures should be examined when supported by history

Avoidance may prevent additional immune stimulation

Exposure history

Identify plausible agent

Remove if possible

Reassess eruption

Schematic

Slide 60 · Topical corticosteroids interrupt inflammation

Mild-to-moderate eczema is commonly treated with topical anti-inflammatory agents

Corticosteroids blunt the inflammatory response during flares

Their benefit as palliative rather than causal eradication

Slide 61 · Severe disease may respond to cytokine blockade

Biologic approaches that inhibit cytokine action in severe eczema

IL-4 and IL-13 are identified as relevant Th2-derived mediators

Specific treatment selection is outside a morphology-only diagnosis

Slide 62 · Uncontrolled flares can sustain more inflammation

Continued inciting exposure can drive a recurrent response

Anti-inflammatory treatment interrupts an acute exacerbation

Combine suppression of the eruption with efforts to identify its cause

Trigger exposure

Inflammation

Epidermal injury

Further exacerbation

Schematic

Slide 63 · Case: Pruritic, oozing plaques after plant exposure

A patient develops intensely pruritic, edematous plaques after outdoor plant contact

Some lesions exhibit vesicles and serous exudate

Which exposure mechanism and epidermal feature are most likely?

Slide 64 · Case: A rash follows a newly ingested medication

An eczematous eruption occurs after exposure to an ingested medication

Biopsy: Spongiosis and perivascular inflammatory cells including eosinophils

What does this finding contribute—and what does it not prove?

Slide 65 · Case: Transient wheals without epidermal change

A patient has pruritic edematous wheals

Biopsy shows superficial dermal edema but a normal epidermis

Which mechanism is favored over eczematous dermatitis?

Slide 66 · Synthesis: Exposure, immunity and tissue reaction

Trigger / exposure

Skin immune response

Spongiosis / vesicles

Persistent thickening

Etiologic context

Immune recruitment

Acute morphology

Time-dependent change

Slide 67 · Primary reference and scope

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th ed. (2026)

Chapter 25, The Skin: pp. 1028–1029 and 1047–1050

Mechanism contextualized from the textbook’s Chapter 6 discussion of T-cell–mediated reactions

Original published micrographs were not embedded; morphological visuals here are editable schematics