How is allergic dermatitis diagnosed and treated?

Diagnosis and Treatment of Allergic Contact Dermatitis

Patch testing is the gold standard for diagnosing allergic contact dermatitis and should be performed in any patient with persistent or chronic dermatitis when contact allergy is suspected. 1

Diagnostic Approach

Clinical History Assessment

A thorough history should specifically focus on:

• Initial location of symptoms and spread pattern
• Relationship to specific products (cosmetics, personal care products, topical medications)
• Detailed history of all wash products contacting the skin
• Association with particular activities (work, hobbies, sports)
• Improvement during environment changes (weekends, holidays)
• Worsening after sunlight exposure 1

Physical Examination

Look for:

• Erythema and scaling with visible borders
• Acute cases: flares with erythema, vesicles, and bullae
• Chronic cases: lichenification with cracks and fissures
• Distribution pattern related to exposure sites 2

Patch Testing

Patch testing is essential when allergic contact dermatitis is suspected:

• Apply standardized allergens to the skin at standardized concentrations under occlusion
• Readings should be performed on day 2 and day 4, with an additional reading at day 6-7 to catch 10% more positives that may develop later 1
• Positive reactions are graded on a scale of +, ++, or +++ 1

Special Testing Considerations:

• Photopatch testing: For suspected photoallergic contact dermatitis
• Open patch testing: For potential irritants or sensitizers and investigation of contact urticaria 1

Treatment Algorithm

1. Allergen Identification and Avoidance

• Primary treatment is identification and complete avoidance of the causative allergen 1, 3
• Provide patients with written information on allergen sources and alternative products 1
• Use databases like Contact Allergen Management Program to help patients select safe products 4

2. Acute Management

For localized acute allergic contact dermatitis:

• Mid- or high-potency topical corticosteroids (e.g., triamcinolone 0.1% or clobetasol 0.05%) 2

For extensive allergic contact dermatitis (>20% body surface area):

• Systemic corticosteroids (e.g., prednisone) tapered over 2-3 weeks
• Rapid discontinuation can cause rebound dermatitis 2
• Prednisone is FDA-approved for contact dermatitis 5

3. Chronic Management

• Avoid long-term topical corticosteroid use 4
• Consider topical calcineurin inhibitors like pimecrolimus for appropriate cases 6
• For patients unable to avoid allergens, consider:
  • Immunosuppressant therapies
  • Phototherapy
  • Barrier methods 7

Special Considerations

Occupational Contact Dermatitis

• Workplace assessment may be necessary to identify allergens
• Evaluate actual working procedures and processes
• Review Material Safety Data Sheets (MSDS) for all materials 1
• Protective equipment or job modification may be required 1

Children

• Increasing reports of allergic contact dermatitis in children
• Common allergens include nickel, topical antibiotics, preservatives, fragrances, and rubber accelerators 1
• Children with persistent eczematous eruptions, particularly hand and eyelid eczema, should be patch tested 1

Food-Related Contact Dermatitis

• Foods can trigger allergic contact dermatitis (e.g., garlic causing hand dermatitis, mango causing perioral dermatitis) 1
• Systemic contact dermatitis can occur when orally consuming allergens to which one is sensitized through skin 1

Common Pitfalls to Avoid

1. Misdiagnosis: Clinical features alone are unreliable in distinguishing allergic contact from irritant and endogenous dermatitis 1

2. Inadequate testing: Using only standard trays may miss relevant allergens; supplemental series are often needed 1, 8

3. Misinterpretation of reactions: Some allergens (metal salts, fragrances) commonly cause irritant reactions that can be misinterpreted as positive allergic reactions 1

4. Premature patch testing: Defer patch testing for:

   • 6 weeks after UV exposure
   • 3 months after systemic agents
   • 6 months after biological agents 1

5. Poor patient education: Only 17% of patients remember their allergen after 10 years despite 79% remembering they had a positive patch test 1