Patch testing of 490 patients in Hong Kong

Area of Science:

• Dermatology
• Allergology
• Epidemiology

Background:

• Eczema diagnosis can be challenging, with potential for misclassification between endogenous eczema and contact dermatitis.
• Identifying specific allergens is crucial for effective management of eczematous conditions.

Purpose of the Study:

• To investigate the diagnostic yield of patch testing in Hong Kong patients with eczema.
• To identify common contact allergens, particularly traditional Chinese medicine and fragrances, in this population.

Main Methods:

• Patch testing was performed on 490 eczema patients in Hong Kong using standard allergens and patient-suspected substances.
• Initial diagnoses included contact dermatitis, endogenous eczema, and unclassified eczema.
• Re-diagnosis rates and common positive allergens were analyzed post-testing.

Main Results:

• Patch testing led to revised diagnoses in 54 contact dermatitis patients and re-diagnosed 18% of endogenous and 34% of unclassified eczema cases as contact dermatitis.
• The most frequent allergens were fragrance mix (19.5%), nickel sulfate (16.4%), and cobalt chloride (11.3%).
• Soap/detergent (22.0%) and traditional Chinese medicine (17.3%) were the leading causes of contact dermatitis, more prevalent than Western medicine (9.0%) or metals (13.4%).

Conclusions:

• Traditional Chinese medicine is a significant cause of contact dermatitis in Hong Kong.
• Fragrance allergy prevalence is notably high in Hong Kong Chinese compared to other Chinese populations.
• Dermatologists should suspect traditional medications and perform patch testing with suspected substances.