Photoallergic dermatitis from 8-methoxypsoralen

Area of Science:

• Dermatology
• Photobiology
• Immunology

Background:

• Psoriasis vulgaris is a chronic skin condition often treated with photochemotherapy.
• 8-methoxypsoralen combined with UVA (PUVA) is a common treatment for psoriasis.
• Adverse reactions to PUVA, though uncommon, can occur.

Purpose of the Study:

• To report a case of generalized photoallergic dermatitis to 8-methoxypsoralen.
• To confirm the diagnosis of photoallergy using various testing methods.
• To investigate the specific wavelengths and psoralen compounds involved.

Main Methods:

• Clinical observation of a patient with psoriasis vulgaris.
• Diagnostic re-exposure to oral 8-methoxypsoralen and UVA irradiation.
• Phototesting with topical and oral 8-methoxypsoralen using high-intensity UVA sources.
• Histological examination of affected skin.
• Testing with UVB, UVC, and trimethylpsoralen.

Main Results:

• The patient developed generalized photoallergic dermatitis after 16 PUVA treatments.
• Diagnosis was confirmed by positive re-exposure tests and photopatch tests.
• Photoallergy was specific to UVA radiation; UVB and UVC did not elicit a reaction.
• No photoallergy was observed with trimethylpsoralen.

Conclusions:

• 8-methoxypsoralen can induce photoallergic dermatitis in susceptible individuals.
• UVA is the critical wavelength for this specific photoallergy.
• Phototesting is essential for diagnosing and characterizing photoallergic reactions.