Key Facts

Dermatitis herpetiformis (DH) is the cutaneous manifestation of coeliac disease. Despite the name, it has no association with herpes viruses — the term refers to the grouped ('herpetiform') arrangement of vesicles. It is one of the most pruritic skin conditions.

Epidemiology

• Incidence: ~0.8–1.2 per 100,000/year in UK
• M:F ~2:1
• Peak age: 30–40 years (younger than BP)
• More common in Northern European populations
• ~15–25% of coeliac disease patients develop DH

Aetiology

• Coeliac disease: virtually all DH patients have underlying gluten-sensitive enteropathy (often subclinical)
• IgA autoantibodies: against epidermal transglutaminase (eTG) — deposited in dermal papillae
• Gluten sensitivity: IgA anti-tTG cross-reacts with eTG → skin deposition
• HLA association: DQ2 (95%) or DQ8 (5%) — identical to coeliac disease

Pathophysiology

• Dietary gluten → immune response in gut → IgA anti-tTG production → IgA cross-reacts with epidermal transglutaminase (eTG) → granular IgA deposition at dermal papillae → neutrophil recruitment → microabscess formation → subepidermal vesicle formation
• Skin disease lags behind GI disease — IgA deposits persist for months after gluten withdrawal

Typical Presentation

• Intensely pruritic grouped papules, vesicles, and excoriations
• Often so itchy that vesicles are scratched away before being noticed
• Symmetrical distribution on extensor surfaces:
  • Elbows (most common)
  • Knees
  • Buttocks
  • Scalp, posterior hairline
  • Upper back
• Vesicles may be very small and grouped
• Excoriations and crusted papules more commonly seen than intact vesicles

Associated Features

• GI symptoms of coeliac disease (may be absent in >50%): diarrhoea, bloating, weight loss
• Iron deficiency anaemia
• Other autoimmune conditions: thyroid disease, type 1 diabetes

Red Flags

• Severe malabsorption symptoms
• Failure to respond to gluten-free diet (consider alternative diagnosis or poor compliance)
• Development of lymphoma symptoms (weight loss, lymphadenopathy) — rare but important

Bedside

• Clinical assessment: distribution, morphology, excoriations

Bloods

• Anti-tissue transglutaminase (tTG) IgA: screening for coeliac disease (sensitivity ~90% in DH)
• Anti-endomysial antibodies (EMA) IgA: highly specific for coeliac disease
• Total IgA: exclude IgA deficiency (false-negative serology)
• FBC: iron deficiency anaemia, macrocytic anaemia (B12/folate malabsorption)
• G6PD level: BEFORE starting dapsone (risk of severe haemolysis if deficient)

Biopsy

• Perilesional skin biopsy for DIF: granular IgA deposits at the dermal papillae — pathognomonic
• Lesional skin biopsy (H&E): neutrophilic microabscesses at dermal papillae, subepidermal vesicle

GI Investigations

• Duodenal biopsy (OGD): villous atrophy, crypt hyperplasia, intraepithelial lymphocytes (Marsh classification) — even in asymptomatic patients
• HLA-DQ2/DQ8 typing: negative result essentially excludes coeliac/DH

Special Tests

• Anti-epidermal transglutaminase (eTG) antibodies: most specific serological marker for DH (research/specialist use)

Non-Pharmacological

• Strict lifelong gluten-free diet (GFD): definitive treatment
  • Controls both skin and GI disease
  • Skin improvement may take 6–24 months
  • Allows dapsone dose reduction and eventual withdrawal
  • Reduces long-term lymphoma risk
• Dietitian referral: essential for GFD education and monitoring
• Coeliac UK membership: support and resources

Pharmacological

• Dapsone 50–150 mg OD: rapid symptomatic relief (within 24–48 hours)
  • Check G6PD before starting (haemolysis risk)
  • Monitor FBC weekly for first 4 weeks, then 3-monthly
  • Side effects: methaemoglobinaemia, haemolytic anaemia, agranulocytosis (rare)
  • Aim to reduce/stop once GFD controls disease
• Sulfapyridine 500 mg–1.5 g BD: alternative if dapsone not tolerated

Monitoring

• FBC: weekly for 4 weeks, then 3-monthly on dapsone
• Methaemoglobin level if symptomatic
• Annual coeliac disease review: serology, dietetic, DEXA scan

Referral Criteria

• Dermatology: all suspected DH for biopsy and DIF
• Gastroenterology: duodenal biopsy, coeliac disease management
• Dietetics: GFD education

• Excellent prognosis with strict GFD and dapsone
• GFD: skin clearance in 6–24 months; allows dapsone withdrawal in most patients
• Lifelong condition: relapse on gluten reintroduction
• Lymphoma risk: small increased risk of small bowel lymphoma (as with coeliac disease); reduced by GFD
• Dapsone: rapid and dramatic symptom relief but does not treat underlying enteropathy
• Spontaneous remission: may occur in ~10–15% over decades

DH vs Other Blistering Diseases

Dapsone Monitoring