Photopatch testing with different ultraviolet A sources can yield discrepant test results

Area of Science:

• Dermatology
• Photobiology
• Allergy and Immunology

Background:

• Photosensitivity disorders affect a significant patient population, necessitating accurate diagnostic tools.
• Photopatch testing is a crucial method for identifying photoallergic reactions to topical substances.
• The choice of ultraviolet (UV) light source in photopatch testing can influence reaction detection.

Purpose of the Study:

• To evaluate the diagnostic performance of different UV light sources in photopatch testing.
• To compare reactions elicited by UVA-1, UVA-2, and combined UVB/UVA-2 irradiation.
• To assess the concordance of late-onset reactions across different irradiation types.

Main Methods:

• A photopatch test series of 27 substances was applied to 81 patients with suspected photosensitivity.
• Irradiation was performed using UVA-1 (355 nm), UVA-2 (375 nm), and UVB (315 nm) light sources.
• Reactions were assessed for immediate and late-onset responses (D3-D21) compared to non-irradiated controls.

Main Results:

• Photopatch test reactions (PPTR) were observed in 43% of patients.
• UVA-1 elicited significantly more positive reactions (44) compared to UVA-2 (10) on day 3.
• Late-onset reactions showed good concordance between UVA-1 and UVA-2, but combined UVB/UVA-2 occasionally yielded divergent results.

Conclusions:

• The choice of UVA source in photopatch testing can significantly impact the number and type of positive reactions.
• While late-onset reactions are largely concordant between UVA-1 and UVA-2, combined irradiation may reveal discrepancies.
• Clinicians should consider the UV light source used when interpreting photopatch test results for photosensitivity disorders.