Overview
Definition:
Contact dermatitis is an inflammatory skin reaction resulting from direct contact with an exogenous substance
It is broadly classified into irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD)
Patch testing is a crucial diagnostic tool for identifying specific allergens in ACD.
Epidemiology:
Contact dermatitis is a common cause of childhood eczema, particularly ACD
While precise incidence figures in children are scarce, it is estimated to contribute to a significant percentage of atopic dermatitis flares and chronic hand eczema in pediatric populations
Factors like increased environmental exposure and hygiene hypothesis may influence prevalence.
Clinical Significance:
Accurate diagnosis and identification of causative agents are vital in pediatric contact dermatitis to prevent recurrent exposures, alleviate discomfort, improve quality of life, and avoid unnecessary treatments
Patch testing allows for targeted avoidance and informed management strategies, crucial for differentiating ACD from other eczematous conditions in children.
Pediatric Considerations
Age Differences:
Infants and younger children may present with more diffuse eczematous rashes compared to older children or adults, making localization of the contactant challenging
Their immune systems are also still developing, potentially influencing reaction patterns.
Common Pediatric Allergens:
Nickel (jewelry, clothing fasteners), fragrances (lotions, soaps, shampoos), preservatives (in emollients and cosmetics), rubber additives (shoes, gloves), and topical antibiotics (neomycin) are frequent culprits in children.
Interpretation Challenges:
Distinguishing between true allergic reactions and irritant reactions or coincidental findings can be more complex in children
Psychosomatic factors or co-existing atopic dermatitis can also complicate interpretation.
Diagnostic Approach
History Taking:
A detailed history is paramount, focusing on the onset, distribution, and evolution of the rash
Inquire about new products (soaps, detergents, lotions, clothing, toys), exposures to plants (poison ivy/oak), and occupational or hobby-related contacts
Previous diagnoses of eczema or allergies are important
Ask about parental use of similar products.
Physical Examination:
Examine the entire skin surface, noting the morphology (erythema, papules, vesicles, oozing, crusting, lichenification) and distribution of the lesions
Look for characteristic patterns such as linear streaks (plant contact), geometric shapes (improperly applied topical treatments), or patterns corresponding to areas of friction or occlusion.
Differential Diagnosis:
Conditions to consider include atopic dermatitis, viral exanthems, scabies, tinea infections, urticaria, and drug eruptions
Careful examination and history can help differentiate these from contact dermatitis
Patch testing is key for ACD.
Patch Testing Indications:
Patch testing is indicated when ACD is suspected, especially in cases of: chronic or recurrent eczema not responding to standard treatment, atypical distribution of eczema, suspicion of specific allergen exposure, or to confirm a suspected allergy in a child with significant morbidity.
Patch Testing Procedure
Preparation:
Patients should avoid topical corticosteroids to the affected area for 2-7 days and oral steroids for at least 2-4 weeks prior to testing, as these can suppress reactions
Identify suspected allergens based on history and examination
Standardized pet roch e che mical s are used.
Allergen Selection:
A curated series of allergens relevant to pediatric exposure is used, often including a baseline series for general screening and specific allergens based on the child's history
Common pediatric series include nickel, fragrances, preservatives, rubber chemicals, and topical antibiotics
Avoid testing too many allergens at once, especially in younger children.
Application And Occlusion:
The selected allergens are applied to small, non-irritated skin areas on the back, typically using aluminum chambers affixed with hypoallergenic tape
The patches are left in place for 48 hours
Ensure adequate occlusion to maintain contact but avoid excessive pressure.
Interpretation Timing:
Readings are performed at 48 hours (T0) and again at 72-96 hours (T1) to assess both immediate and delayed reactions
A third reading may be necessary in some cases
Standardized scoring systems (e.g., ICDRG scale) are used to grade the intensity of the reaction.
Interpretation And Management
Interpreting Results:
A positive reaction is indicated by erythema, papules, vesicles, or edema at the application site, graded from weak positive (+) to strong positive (++) or extreme positive (+++)
Irritant reactions are typically less intense and localized directly under the chamber
Negative results do not entirely rule out ACD if testing was inadequate or exposure was intermittent.
Managing Positive Results:
Once a specific allergen is identified, the primary management is strict avoidance of that substance
Educate parents and the child about common sources of the allergen
Topical corticosteroids may be prescribed to manage acute flares of ACD
Short courses of oral corticosteroids may be needed for severe, widespread reactions.
Follow Up And Education:
Regular follow-up is essential to ensure compliance with avoidance strategies and to monitor skin health
Educate parents on reading product labels and identifying potential hidden sources of the allergen
Consider re-testing if there are doubts about the initial interpretation or if new suspected exposures arise.
Complications And Limitations
False Positives:
Irritant reactions can mimic ACD, especially with highly concentrated or irritating substances
Co-existing atopic dermatitis can also lead to exaggerated responses
Careful allergen selection and interpretation are key.
False Negatives:
These can occur due to inadequate allergen concentration, poor occlusion, interference from topical or systemic steroids, very dilute exposures, or recent intermittent contact
The patient may also have developed tolerance.
Testing Challenges In Children:
Achieving adequate occlusion, ensuring the child cooperates during application and removal, and managing potential local irritation from the tape or chambers can be difficult
Discomfort during testing can also be a factor.
Key Points
Exam Focus:
Understand the difference between ICD and ACD
Know the indications for patch testing in pediatric dermatitis
Recognize common pediatric allergens
Be familiar with patch test application, reading schedule, and interpretation scales (e.g., ICDRG).
Clinical Pearls:
Always correlate patch test results with the clinical presentation and history
Involve parents actively in allergen avoidance
Consider that a positive reaction to a chemical doesn't always mean it's the cause of the current dermatitis
temporal association is crucial.
Common Mistakes:
Failing to take a thorough history of exposures
Misinterpreting irritant reactions as allergic
Over-testing with too many allergens
Not emphasizing strict allergen avoidance post-testing
Relying solely on patch testing without clinical correlation.