What is the cause of this extremely itchy bilateral wrist rash?

Epidemiology

• Most common in adults aged 30–50, but can occur at any age.
• Male predominance (2:1).
• Strongly associated with coeliac disease, although many have no GI symptoms.

Clinical features

Presentation:
• Intensely pruritic, symmetrical eruption of erythematous papules, vesicles and excoriations, often in clusters.
• Vesicles are fragile and often not visible due to scratching.
• Chronic, relapsing course; symptoms may fluctuate with dietary gluten exposure.

Symptoms:
• Severe itching or burning is a hallmark; often precedes visible lesions.
• Gastrointestinal symptoms (eg, bloating, diarrhoea) are often absent, despite underlying coeliac disease.
• Systemic symptoms are rare.

Affected areas:
• Extensor surfaces: elbows, knees, buttocks, shoulders, and scalp are classic sites.
• Facial and scalp involvement is less common but can occur.
• Oral mucosa is typically spared (unlike lichen planus).

Diagnosis

Clinical evaluation:
• Suspect in patients with intensely itchy rash on extensor surfaces, especially if recurrent or treatment-resistant.
• Ask about GI symptoms, family history of coeliac disease, and dietary triggers.

Investigations:
• Skin biopsy from perilesional skin (not the blister): direct immunofluorescence showing granular IgA deposits at dermoepidermal junction confirms diagnosis.
• Coeliac serology.
• Consider coeliac disease workup, even if asymptomatic.

Differential diagnosis

• Scabies: Pruritus often worse at night; burrows; different distribution.
• Atopic eczema: More flexural involvement; earlier onset.
• Psoriasis: Well-demarcated plaques with silvery scale; typically non-vesicular; less itchy.
• Linear IgA disease: Vesicles, but typically younger onset and different immunofluorescence pattern.
• Bullous pemphigoid: Elderly patients; larger tense bullae; different histology.

Red flags

• Misdiagnosis as eczema or scabies is common – consider DH in persistent/extremely itchy symmetrical rashes.
• Unrecognised coeliac disease: Risk of long-term complications (eg, osteoporosis, lymphoma).
• Delayed diagnosis can significantly impact quality of life due to itching and ongoing intestinal inflammation.

Management

First-Line:
• Gluten-free diet (GFD) – cornerstone of long-term management; often improves skin symptoms within months.
• Refer to dietitian with coeliac expertise.
• Ensure B12, folate, iron, vitamin D and calcium are checked.

Symptom control:
• Dapsone (unlicensed): Rapid relief of itch and rash (usually overseen by specialist).
• Topical corticosteroids may help with itch but are generally insufficient alone.

Refractory or severe disease:
• Dermatology referral for immunosuppressive alternatives.
• Ongoing monitoring and support for GFD adherence.

Patient education

Understanding the condition:
• DH is a chronic, autoimmune blistering skin disease linked to coeliac disease.
• Not infectious or cancerous.
• A strict gluten-free diet is essential and often lifelong.

Triggers and associations:
• Gluten ingestion triggers immune response in skin and gut.
• Explain that skin symptoms may improve before gut histology normalises.
• Educate on label reading and hidden sources of gluten.

When to refer:
• Diagnostic uncertainty or atypical features.
• Poor response to GFD and/or dapsone.
• Concerns over dapsone tolerance or side effects.
• For confirmation of diagnosis via skin biopsy (dermatology) or coeliac workup (gastroenterology if needed).