A 45 year old farmer has itchy erythematous papular lesions on face, neck, ‘V‘ area of chest, dorsum of hands and forearms for 3 years. The lesions are more severe in summer and improve by 75% in winter. The most appropriate test to diagnose the condition would be:
A. Skin biopsy
B. Estimation of IgE levels in blood
C. Patch test
D. Intradermal prick test
Correct answer : C. Patch test
The history is suggestive of photodermatitis. Patch test is used for diagnosis of photodermatitis.
Patch test (photopatch test) : Here, 2 patches containing photosensitising material is applied on 2 different sites on the body. One of them is irradiated with UVA rays. The other is kept as control. Development of eczema is looked for upto 72 hours.
Analysis of results:
- No development of eczema – patient does not have photodermatitis
- Development of eczema under the patch irradiated with UVA – Photodermatitis
- Development of eczema under both patches – Contact dermatitis