What are the diagnostic criteria for contact dermatitis?

Diagnostic Criteria for Contact Dermatitis

Contact dermatitis is diagnosed clinically based on a detailed exposure history, characteristic morphology and distribution of eczematous lesions, and patch testing to distinguish allergic from irritant forms, as clinical features alone cannot reliably differentiate between these subtypes. 1, 2

Essential Clinical Features

Contact dermatitis presents with varying degrees of erythema, vesiculation, scaling, and lichenification, though these findings overlap significantly with other eczematous conditions 3, 4. The diagnosis requires:

• Eczematous skin lesions with erythema and pruritus that occur after contact with a foreign substance 5
• Acute presentations showing erythema, vesicles, bullae, and edema 2, 5
• Chronic presentations demonstrating dryness, scaling, lichenification, fissuring, and cracks 2, 5
• Visible borders to the dermatitis that correspond to areas of contact 5

Critical History Elements

The British Association of Dermatologists emphasizes that pattern and morphology alone are unreliable for determining etiology, making a detailed history essential 1:

Personal and Family Background

• Personal history of atopic dermatitis in infancy/childhood and presence of asthma or hay fever 1
• Family history of atopy 1

Temporal and Spatial Patterns

• Location where initial symptoms began and subsequent spread pattern 1
• Whether symptoms improve with environmental changes (weekends, holidays, away from work) and recur upon return 1, 2
• Relationship to sunlight exposure 1

Exposure Assessment

• Product-related exposures: cosmetics, personal-care products, topical medications, clothing, bandages, gloves 1
• Detailed wash product history: most contain harsh emulsifiers/surfactants that damage skin barrier in predisposed individuals 1
• Activity-related exposures: hairdressing, holidays, home improvements, painting, decorating, recreation, sport 1
• Occupational exposures: specific workplace activities, products handled, review of Material Safety Data Sheets 1, 2
• Irritant exposures: both wet agents (water, frequency of hand washing) and dry, desiccating products 1, 2

Distinguishing Allergic from Irritant Contact Dermatitis

Allergic Contact Dermatitis (ACD)

• Cell-mediated delayed hypersensitivity reaction occurring only in sensitized individuals with predisposition to specific allergens 1
• Requires prior sensitization through skin contact, followed by elicitation upon re-exposure 5, 6
• Diagnosis confirmed by positive patch testing with eczematous reactions assessed at 48-72 hours 1
• Positive reactions must be distinguished from simple irritant reactions and assessed for clinical relevance in context 1

Irritant Contact Dermatitis (ICD)

• Non-immune-modulated irritation caused by toxic reaction to substances 5, 6
• Diagnosed primarily by exclusion after ruling out ACD through negative patch testing 2
• Requires documentation of single overwhelming exposure or repetitive exposure to weak irritants (detergents, solvents, soaps, water) 2
• Water itself acts as an irritant, particularly with frequent hand washing 2

Patch Testing: The Gold Standard

Patch testing is the gold-standard investigation when allergic contact dermatitis is considered and must be performed because clinical features alone cannot reliably distinguish allergic from irritant or endogenous dermatitis. 1, 2

Indications for Patch Testing

• Suspected allergic contact dermatitis based on history and distribution 1, 7
• Persistent or recalcitrant dermatitis despite treatment 8
• Unusual distribution patterns 8
• Later onset or new worsening of dermatitis 8
• Even when irritant contact dermatitis seems clinically obvious 2

Patch Testing Methodology

• Standardized contact allergens or suspected allergens applied to healthy skin 1
• Eczematous reactions assessed at 48-72 hours 1
• Sensitivity of 60-80% for detecting allergic contact dermatitis 8
• Dermatologists select appropriate allergens, assess products patients bring, and determine relevance 1

Important Testing Considerations

• Immunosuppressive treatment can yield suboptimal but preferable results compared to not testing 1
• Antihistamines do not need to be avoided unless testing for urticaria 1
• Extended allergen series needed for specific anatomical sites, occupational groups, and chemical exposures 1

Special Diagnostic Scenarios

Food-Related Contact Dermatitis

• Immediate reactions initiated by chemical moieties in foods (oleoresins in fruits/vegetables, spices) 1
• Examples include garlic causing hand dermatitis, mango causing perioral dermatitis, raw chestnut causing hand/perianal dermatitis 1, 8
• Patch testing with suspected food allergens can diagnose this, though sIgE testing usually negative 1

Systemic Contact Dermatitis

• Rare disorder with generalized eczematous dermatitis plus systemic symptoms (fever, headache, rhinitis, GI complaints) 1
• Develops after oral/parenteral exposure to allergen with prior skin sensitization 1
• Metals (nickel, cobalt, chromium) and fragrances (Balsam of Peru) are important allergens 1
• Diagnosed using medical history showing symptom resolution with food avoidance and positive patch tests 1

IgE-Mediated Contact Urticaria

• Diagnosed using medical history with symptom absence during food avoidance, positive sIgE tests or SPTs, and positive immediate epicutaneous skin tests 1
• Substances in foods interact with sIgE bound to cutaneous mast cells 1

Common Diagnostic Pitfalls

Critical Errors to Avoid

• Failing to consider contact dermatitis in patients with known atopic dermatitis: allergic contact dermatitis occurs in 6-60% of atopic dermatitis patients 8
• Relying solely on clinical appearance: irritant contact dermatitis is indistinguishable from endogenous, dyshidrotic, nummular, and atopic dermatitis 2
• Overlooking occupational or hobby-related exposures to irritants or allergens 8
• Assuming absence of occupational exposure rules out irritant contact dermatitis 2
• Skipping patch testing when irritant contact dermatitis seems clinically obvious 2
• Not recognizing that multiple conditions can coexist (irritant contact dermatitis, allergic contact dermatitis, and atopic dermatitis) 8

Assessment Tools

• Use clinical assessment tools for initial assessment and treatment response monitoring 1
• Generic tools: Dermatology Life Quality Index 1
• Specific objective scoring: Hand Eczema Severity Index 1
• Simplified tools (Investigators Global Assessment): quick but only useful for chronic hyperkeratotic hand dermatitis, not pompholyx 1

Diagnostic Algorithm

1. Obtain detailed exposure history covering personal/family atopy, temporal patterns, product exposures, activities, occupational factors, and irritant contacts 1, 2
2. Perform clinical examination documenting morphology, distribution, and borders of eczematous lesions 1, 5
3. Assess response to avoidance of suspected causative substance 1, 5
4. Conduct patch testing to confirm allergic contact dermatitis and rule out allergens even when irritant contact dermatitis suspected 1, 2
5. Correlate patch test results with clinical history and examination findings to determine clinical relevance 1, 6
6. Provide clear communication of relevant allergen information to allow identification, avoidance, or substitution 1