Photopatch testing-- a retrospective review using the 1 day and 2 day irradiation protocols

Area of Science:

• Dermatology
• Photodermatology
• Allergy Testing

Background:

• Photopatch testing investigates eczematous eruptions on sun-exposed skin, especially with a history of sun sensitivity.
• Existing British Photodermatology Group protocols involve allergen irradiation 1 or 2 days post-application, with no proven superiority.

Purpose of the Study:

• To compare the sensitivity of 1-day versus 2-day occlusion periods before allergen irradiation in photopatch testing.
• To evaluate the clinical relevance and indicative nature of photoallergic reactions detected.

Main Methods:

• Retrospective review of photopatch testing records from Leeds over 50 months.
• Allergens applied in triplicate: one set irradiated after 1 day occlusion, another after 2 days; control occluded for 2 days.
• Readings performed at 2 and 4 days post-application.

Main Results:

• 15 of 74 patients had 49 positive results, with 43 deemed clinically relevant.
• 34 positive results indicated photoallergy.
• 2 days occlusion detected more photoallergic reactions (16) compared to 1 day occlusion (5).

Conclusions:

• The study suggests 2 days occlusion before allergen irradiation is more sensitive for detecting photoallergy.
• This finding may refine photopatch testing protocols for improved diagnosis of photoallergic reactions.