Dermatitis Herpetiformis

Slide 1 · Dermatitis herpetiformis

An autoimmune gluten-sensitive vesiculobullous dermatosis

Gluten-associated autoimmunity

Papillary neutrophils

Granular IgA

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Mechanistic explanation

Morphologic interpretation

Immunofluorescence diagnosis

Differential reasoning

Slide 3 · The diagnostic signature

Clinical pattern

Pruritic grouped extensor eruption

H&E anatomy

Neutrophils at papillary tips

Direct IF

Granular papillary IgA

Slide 4 · DH belongs among inflammatory blistering disorders

Autoimmune injury occurs at the dermoepidermal interface.

The separation plane is subepidermal: The epidermis forms the blister roof.

This is distinct from intraepidermal acantholysis in pemphigus.

Subcorneal

Suprabasal

Subepidermal

Slide 5 · Skin architecture: The relevant compartments

Epidermis rests on a specialized basement-membrane zone.

Dermal papillae project toward the basal epidermis.

Anchoring structures stabilize the epidermis–dermis attachment.

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 6 · Why the blister roof remains intact

Subepidermal cleavage lifts the full thickness of epidermis.

The blister is initially mechanically more stable than a superficial split.

Rupture and excoriation may later obscure the intact vesicle.

Subcorneal

Suprabasal

Subepidermal

Slide 7 · IgA autoimmunity is the defining mechanism

IgA is the predominant immunoglobulin in the diagnostic deposits.

Immune-mediated injury recruits inflammatory cells at the junction.

Histologic injury occurs beneath, not between, keratinocytes.

Granular IgA deposits

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 8 · Who develops the disease?

Male predominance and frequent presentation in the third or fourth decade.

Contemporary cohorts also include older adults; Age distribution varies by population.

Demographics support suspicion but cannot establish or exclude DH.

INTERPRET IN CONTEXT

Clinical phenotype

+ immunopathology

+ supportive tests

Slide 9 · The celiac disease association

A greater than 100-fold increased DH risk in people with celiac disease.

DH is widely considered a cutaneous manifestation of gluten-sensitive enteropathy.

Cutaneous symptoms may dominate even when bowel symptoms are minimal.

Dietary gluten

Gluten-sensitive immunity

IgA / TG3 response

Granular dermal deposits

Slide 10 · Classical and contemporary autoantigens

IgA reactivity with reticulin / anchoring-fibril components.

Contemporary literature identifies epidermal transglutaminase (TG3) as the principal DH autoantigen.

Distinguish the textbook framing from the newer molecular explanation.

TG2

Intestinal autoimmunity

Celiac-related serology

TG3

Skin-directed autoantigen

DH-related serology

Related—not interchangeable—targets

Slide 11 · Inherited susceptibility: HLA-DQ2 and HLA-DQ8

These HLA haplotypes facilitate gluten-associated immune responses.

Their presence is common in the general population and is not diagnostic.

Absence can help exclude the disease in an equivocal evaluation.

INTERPRET IN CONTEXT

Clinical phenotype

+ immunopathology

+ supportive tests

Slide 12 · Dietary gluten initiates the gut–skin axis

Gluten-related peptides provoke a mucosal immune response in predisposed hosts.

Celiac-associated immune dysregulation precedes or accompanies DH.

Cutaneous disease is linked to persistent gluten exposure.

Dietary gluten

Gluten-sensitive immunity

IgA / TG3 response

Granular dermal deposits

Slide 13 · Tissue transglutaminase versus epidermal transglutaminase

TG2: Central autoantigen in celiac enteropathy and a common serologic target.

TG3: Primary cutaneous autoantigen associated with DH.

Serologic and tissue autoantigens overlap, but are not identical.

TG2

Intestinal autoimmunity

Celiac-related serology

TG3

Skin-directed autoantigen

DH-related serology

Related—not interchangeable—targets

Slide 14 · A mechanistic sequence from gluten to skin injury

Gluten exposure in a susceptible host.

Gluten-associated autoimmunity with IgA targeting TG3.

Granular dermal IgA deposition and neutrophil-dominant injury.

Gluten exposure

Immune response

IgA–TG3 deposits

Papillary neutrophils

Subepidermal split

Slide 15 · Where IgA accumulates

The characteristic pattern is discontinuous and granular.

Deposits emphasize the tips of the dermal papillae.

Unlike pemphigoid, the defining pattern is not a smooth continuous IgG line.

Fluorescent IgA-positive granules (schematic)

Read the deposit pattern and its anatomic location

Slide 16 · Why neutrophils are recruited

Granular immune deposition is associated with a local inflammatory reaction.

Neutrophils concentrate in the papillary dermis.

Inflammatory injury damages the basal junction and facilitates cleavage.

Papillary neutrophils

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 17 · Papillary microabscesses: The early microscopic clue

Dense clusters of neutrophils form in papillary tips.

Fibrin may accompany the neutrophils.

The overlying epidermis may still be largely attached.

Papillary neutrophils

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 18 · From microabscess to vesicle

Early papillary inflammation causes basal vacuolization.

Focal separations develop at the dermoepidermal junction.

Adjacent foci can merge into an established subepidermal blister.

Neutrophilic focus

Basal injury

Coalescent split

Slide 19 · Pruritus is often the dominant complaint

The lesions are intensely itchy, commonly before vesicles are noticed.

Persistent scratching creates erosions and crusts.

Clinical severity may be disproportionate to the number of intact blisters.

Grouped papules and vesicles

Intense itch → scratching

Erosions, crust and pigmentation

Slide 20 · Grouped vesicles and urticarial plaques

The eruption contains small, grouped vesicles on erythematous or urticarial skin.

Papules, erosions, and excoriations can coexist.

The term “herpetiformis” describes arrangement—not herpesvirus infection.

Grouped papules and vesicles

Intense itch → scratching

Erosions, crust and pigmentation

Slide 21 · Typical distribution: Extensor predominance

Elbows and knees are characteristic sites.

Buttocks and upper back are also common.

The bilateral, symmetric pattern adds diagnostic weight.

Elbows

Elbows

Knees

Knees

Buttocks / back

Mirror-image involvement is common

Slide 22 · Symmetry as a clinical discriminator

Lesions frequently occur on corresponding sites on both sides.

Symmetry should prompt an autoimmune / systemic mechanism in context.

Asymmetry or limited sites do not automatically exclude DH.

Elbows

Elbows

Knees

Knees

Buttocks / back

Mirror-image involvement is common

Slide 23 · The scratch can erase the blister

Intact vesicles may be absent in a heavily excoriated eruption.

Crust, scratch marks and postinflammatory changes can dominate.

Biopsy selection should avoid a denuded, heavily scratched center.

Grouped papules and vesicles

Intense itch → scratching

Erosions, crust and pigmentation

Slide 24 · Appearance in darker skin tones

The eruption may look hyperpigmented rather than vividly erythematous.

Excoriations and residual pigment can be prominent.

Evaluate site, symmetry, grouping and pruritus—not erythema alone.

Grouped papules and vesicles

Intense itch → scratching

Erosions, crust and pigmentation

Slide 25 · Few gastrointestinal symptoms do not exclude DH

Many patients have intestinal pathology without overt diarrhea.

A skin presentation may be the first recognized sign of gluten sensitivity.

Gastrointestinal assessment follows confirmed disease even without bowel complaints.

Dietary gluten

Gluten-sensitive immunity

IgA / TG3 response

Granular dermal deposits

Slide 26 · Why the name is misleading

“Herpetiform” refers to grouped vesicles resembling herpes distribution.

DH is not caused by herpes simplex or varicella-zoster virus.

Pruritus, extensor symmetry, and granular IgA favor DH over herpes infection.

Pruritus is nonspecific

Symmetric extensor papulovesicles suggest DH

Definitive classification needs immunopathology

Slide 27 · Two samples answer two different questions

Lesional skin in formalin: Hematoxylin–eosin morphology.

Perilesional normal-appearing skin in DIF medium: Tissue-bound IgA.

A poorly selected specimen can yield a misleading negative study.

LESIONAL

H&E

Tissue morphology

PERILESIONAL

DIF

Granular IgA

Separate biopsies • correct medium and site

Slide 28 · Read the lesional H&E in a fixed sequence

First: Identify intraepidermal versus subepidermal separation.

Second: Inspect neutrophils within individual papillary tips.

Third: Assess vacuolization, edema, fibrin and secondary scratching.

Papillary neutrophils

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 29 · Early histology: Dermal papillary inflammation

Neutrophils collect at the apex of papillae.

Small superficial foci precede a fully developed blister.

Subtle changes require careful inspection of multiple levels.

Papillary neutrophils

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 30 · Evolving lesion: Basal injury and cleavage

Vacuolization appears in the basal keratinocytes.

Multiple focal junctional defects develop.

The epidermis lifts as damage coalesces.

Neutrophilic focus

Basal injury

Coalescent split

Slide 31 · Established lesion: Subepidermal cavity

The epidermis forms the complete roof of the blister.

The cavity may contain inflammatory cells and proteinaceous fluid.

Papillary neutrophilic collections support DH when identifiable.

Subepidermal cleft

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 32 · Inflammatory-cell pattern has diagnostic value

Neutrophils in dermal papillae are a hallmark.

A minority of eosinophils may also be encountered in lesional biopsies.

Neutrophilic histology alone does not uniquely identify DH.

Neutrophils

Papillary microabscesses

Eosinophils

May be present but are not defining

Pattern + location outperform cell type alone

Slide 33 · Acantholysis is not the principal DH lesion

Acantholysis is loss of cohesion among epidermal keratinocytes.

Pemphigus produces intraepidermal acantholytic blisters.

DH produces interface injury with subepidermal separation.

Subcorneal

Suprabasal

Subepidermal

Slide 34 · Why H&E findings can be insufficient

Scratch injury can conceal the primary blister morphology.

Early lesions may show papillary inflammation without a definitive cavity.

Histology and clinical context should be integrated with DIF.

Papillary neutrophils

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 35 · Direct immunofluorescence: What is examined?

DIF detects immunoreactants already deposited within patient skin.

An anti-human IgA fluorescent reagent highlights their tissue location.

Pattern and anatomic compartment are interpreted together.

Fluorescent IgA-positive granules (schematic)

Read the deposit pattern and its anatomic location

Slide 36 · Granular papillary IgA is the central diagnostic finding

Granular IgA appears in the papillary dermis, especially papillary tips.

Deposits are discontinuous rather than a smooth linear band.

A compatible DIF strongly supports the diagnosis of DH.

Fluorescent IgA-positive granules (schematic)

Read the deposit pattern and its anatomic location

Slide 37 · Granular IgA may track the junction

Papillary-tip deposits are classic.

Other described DH patterns include granular deposits along the junction.

Do not equate every junctional IgA signal with a continuous linear IgA disease pattern.

Fluorescent IgA-positive granules (schematic)

Read the deposit pattern and its anatomic location

Slide 38 · Biopsy site for DIF: Perilesional skin

Sample normal-appearing skin immediately adjacent to an active lesion.

Avoid a ruptured blister or a severely inflamed/excoriated area.

Use the laboratory’s dedicated DIF transport protocol, not routine formalin.

LESIONAL

H&E

Tissue morphology

PERILESIONAL

DIF

Granular IgA

Separate biopsies • correct medium and site

Slide 39 · A negative DIF requires clinical interpretation

Check whether sampling and handling were appropriate.

Long-term gluten avoidance can reduce IgA deposits and test positivity.

If suspicion remains high, consider expert review and repeat properly sited DIF.

Clinical pattern

H&E + perilesional DIF

Granular IgA?

Integrate serology / celiac evaluation

Slide 40 · Granular versus linear deposition

DH: Granular IgA emphasized at papillary tips.

Linear IgA bullous dermatosis: Linear IgA along the junction.

Bullous pemphigoid: Usually linear IgG and/or C3 at the junction.

Fluorescent IgA-positive granules (schematic)

Granular papillary IgA (DH)

Continuous linear junctional IgA (linear IgA disease)

Slide 41 · Serology supplements—but does not replace—DIF

TG2 IgA and endomysial IgA support gluten-sensitive enteropathy.

TG3 IgA can increase support for cutaneous disease.

Negative blood tests do not automatically overturn convincing cutaneous DIF.

IgA anti-TG2: Celiac-related

IgA anti-TG3: DH-related

Total IgA: Assay interpretation

Supportive information; Interpret with DIF

Slide 42 · Tissue transglutaminase IgA: Interpret the target

Anti-TG2 IgA is a commonly used celiac-related serologic marker.

Positivity supports gluten-associated autoimmunity.

An isolated result is not a substitute for correct immunopathology.

IgA anti-TG2: Celiac-related

IgA anti-TG3: DH-related

Total IgA: Assay interpretation

Supportive information; Interpret with DIF

Slide 43 · TG3 IgA: A disease-relevant serologic target

Epidermal transglutaminase is the principal recognized DH autoantigen.

Anti-TG3 assays may be helpful when conventional celiac serology is negative.

Access and performance vary by testing platform.

IgA anti-TG2: Celiac-related

IgA anti-TG3: DH-related

Total IgA: Assay interpretation

Supportive information; Interpret with DIF

Slide 44 · IgA status matters when interpreting serology

An IgA-based assay may be misleading in IgA deficiency.

Total serum IgA helps contextualize negative IgA antibody results.

An appropriate IgG-based celiac testing strategy can be considered if deficient.

IgA anti-TG2: Celiac-related

IgA anti-TG3: DH-related

Total IgA: Assay interpretation

Supportive information; Interpret with DIF

Slide 45 · HLA testing is an exclusion aid, not confirmation

HLA-DQ2 or DQ8 supports genetic susceptibility.

A positive result is not disease-specific because these alleles are common.

Testing is most useful when clinical, DIF, and serology results conflict.

INTERPRET IN CONTEXT

Clinical phenotype

+ immunopathology

+ supportive tests

Slide 46 · When is intestinal biopsy considered?

Classic cutaneous DIF may already establish DH as a manifestation of celiac disease.

Small-bowel biopsy is not mandatory solely to confirm established DH.

Additional gastrointestinal indications require individualized assessment.

Dietary gluten

Gluten-sensitive immunity

IgA / TG3 response

Granular dermal deposits

Slide 47 · Assess associated enteropathy and its consequences

Ask about bowel symptoms, nutritional status and anemia.

Assess autoimmune comorbidity and intestinal complications as indicated.

Coordinate care across dermatology, gastroenterology and nutrition.

Dietary gluten

Gluten-sensitive immunity

IgA / TG3 response

Granular dermal deposits

Slide 48 · A rational diagnostic pathway

Recognize the patterned, highly pruritic eruption.

Obtain lesional H&E and perilesional DIF using separate specimens.

Interpret granular IgA with supported serology and celiac assessment.

Clinical pattern

H&E + perilesional DIF

Granular IgA?

Integrate serology / celiac evaluation

Slide 49 · Bullous pemphigoid: The nearest structural mimic

Both DH and bullous pemphigoid can create subepidermal blisters.

Bullous pemphigoid typically shows more eosinophils and a continuous linear junctional pattern.

Pattern of immunoreactants is more discriminating than blister level alone.

DH

Papillary neutrophils

Granular IgA

Bullous pemphigoid

Often eosinophils

Linear IgG / C3

Slide 50 · Linear IgA bullous dermatosis: DIF distinguishes

Both may show neutrophils and subepidermal cleavage.

Linear IgA disease demonstrates a smooth IgA line at the junction.

DH classically shows granular IgA in dermal papillary tips.

Fluorescent IgA-positive granules (schematic)

Granular papillary IgA (DH)

Continuous linear junctional IgA (linear IgA disease)

Slide 51 · Pemphigus: A different adhesion failure

Pemphigus commonly exhibits intraepidermal acantholysis.

Autoantibodies target desmosomal structures rather than papillary IgA complexes.

The split level and DIF localization separate it from DH.

Subcorneal

Suprabasal

Subepidermal

Slide 52 · Common nonbullous mimics

Eczema, scabies and prurigo can cause severe itch and excoriations.

An absence of intact vesicles does not distinguish these from DH.

Distribution, treatment history and selected investigations guide evaluation.

Pruritus is nonspecific

Symmetric extensor papulovesicles suggest DH

Definitive classification needs immunopathology

Slide 53 · Other neutrophilic subepidermal blistering disorders

Neutrophilic morphology is shared by several autoimmune dermatoses.

Consider linear IgA disease and other rare interface blistering diseases.

Definitive classification depends on DIF pattern and context.

DH

Papillary neutrophils

Granular IgA

Bullous pemphigoid

Often eosinophils

Linear IgG / C3

Slide 54 · The diagnostic comparison in one table

Disease

Split

Main H&E clue

DIF

DH

Subepidermal

Papillary neutrophils

Granular IgA

Pemphigoid

Subepidermal

Often eosinophils

Linear IgG/C3

Linear IgA

Subepidermal

Often neutrophils

Linear IgA

Pemphigus

Intraepidermal

Acantholysis

Intercellular IgG

Slide 55 · A gluten-free diet treats the driver

Strict lifelong gluten avoidance is disease-modifying for skin and bowel disease.

Resolution of the immunologic process can be slower than symptomatic treatment.

Dietetic support helps maintain adherence and nutritional adequacy.

Dietary gluten

Gluten-sensitive immunity

IgA / TG3 response

Granular dermal deposits

Slide 56 · Diet response is not an immediate diagnostic test

Skin improvement may take months; Full control can require a longer interval.

DIF and some serologies become less informative after prolonged gluten avoidance.

Do not delay diagnostic sampling in a patient still consuming gluten.

Diagnosis

Early symptom control

Diet-mediated improvement

Long-term follow-up

Slide 57 · Dapsone provides rapid symptomatic control

Dapsone can relieve pruritus and lesions while dietary treatment takes effect.

It does not replace lifelong gluten avoidance.

Treatment decisions require assessment of risks and monitoring.

Gluten-free diet: Underlying driver

Dapsone: Rapid symptom suppression

Both require appropriate follow-up

Slide 58 · Dapsone: Monitoring is integral to prescribing

Important risks include hemolysis and methemoglobinemia.

Check relevant baseline measures, including G6PD status and blood counts, per local protocol.

Ongoing monitoring includes blood counts and other safety tests as clinically indicated.

Gluten-free diet: Underlying driver

Dapsone: Rapid symptom suppression

Both require appropriate follow-up

Slide 59 · Follow-up combines cutaneous and systemic endpoints

Document itch, active lesions and dapsone requirement.

Review diet adherence, nutrition and evidence of enteropathy.

Track indicated comorbidities rather than focusing on the rash alone.

Diagnosis

Early symptom control

Diet-mediated improvement

Long-term follow-up

Slide 60 · Persistent rash: Reassess the cause

First consider inadvertent gluten exposure or imperfect dietary adherence.

Reevaluate diagnosis if clinical or DIF findings were atypical.

Assess treatment tolerance and alternative pruritic disorders.

Clinical pattern

H&E + perilesional DIF

Granular IgA?

Integrate serology / celiac evaluation

Slide 61 · Associated conditions deserve clinical attention

Celiac-associated nutritional abnormalities may accompany DH.

Autoimmune thyroid disease is an established association.

Long-term intestinal risk assessment belongs within celiac care.

Dietary gluten

Gluten-sensitive immunity

IgA / TG3 response

Granular dermal deposits

Slide 62 · Prognosis depends on sustained disease control

Lifelong diet is the central long-term intervention.

Medication needs often diminish when gluten avoidance is sustained.

Multidisciplinary management supports durable clinical control.

Diagnosis

Early symptom control

Diet-mediated improvement

Long-term follow-up

Slide 63 · Case: Symmetric excoriated plaques on the elbows

An adult has severe itch, grouped erosions on both elbows and buttocks.

Routine H&E reveals papillary-tip neutrophilic aggregates.

What additional test most directly confirms suspected DH?

Clinical problem

Identify the most informative next diagnostic action and explain why.

Slide 64 · Case answer: Biopsy adjacent normal skin for DIF

Obtain perilesional clinically uninvolved skin for DIF.

Look for granular IgA deposits at papillary dermal tips.

A gluten-associated serologic assessment is supportive rather than a replacement.

Fluorescent IgA-positive granules (schematic)

Read the deposit pattern and its anatomic location

Slide 65 · Case: Pruritus and negative serology

A patient has classic distribution and an H&E-compatible lesion.

Anti-TG2 IgA is negative; Biopsy for DIF came from an eroded vesicle.

Which uncertainty should be resolved first?

Clinical problem

Identify the most informative next diagnostic action and explain why.

Slide 66 · Case answer: Reassess sampling and IgA status

An eroded blister is a suboptimal DIF specimen.

Repeat properly sited DIF if clinical suspicion remains high.

Consider total IgA and disease-relevant serology in context.

LESIONAL

H&E

Tissue morphology

PERILESIONAL

DIF

Granular IgA

Separate biopsies • correct medium and site

Slide 67 · Morphology application: Identify the primary lesion

Papillary-tip neutrophils plus focal basal separation suggest early DH.

An established cavity below the entire epidermis confirms the cleavage plane.

Granular IgA distinguishes DH from several morphologic mimics.

Subepidermal cleft

Epidermis

Papillary dermis

Schematic — not a tissue specimen

Slide 68 · Common interpretive errors

Treating a negative lesional DIF sample as definitive exclusion.

Confusing papillary granular IgA with a continuous linear junctional pattern.

Assuming absent gastrointestinal symptoms means no celiac-related disease.

Sampling site can make DIF falsely negative

Granular ≠ linear IgA

Silent enteropathy remains relevant

Slide 69 · Integrated clinicopathologic conclusion

Clinical pattern

Pruritic grouped extensor eruption

H&E anatomy

Neutrophils at papillary tips

Direct IF

Granular papillary IgA

Slide 70 · Key references

Robbins, Cotran & Kumar. Pathologic Basis of Disease, 11th ed.; Chapter 25.

EADV S2k consensus guideline on DH (2021).

Nguyen & Kim. Medicina (2021); Reunala et al. Am J Clin Dermatol (2021).

NIDDK professional resource; Didona et al. review (2025).

Primary source

Robbins 11th edition

Supplementary references

EADV consensus • NIH • peer-reviewed reviews