Solar urticaria: mechanism and treatment

Area of Science:

• Dermatology
• Photobiology
• Immunology

Background:

• Solar urticaria is a rare photodermatosis characterized by wheal-and-flare reactions upon sun exposure.
• The specific wavelengths and mechanisms triggering solar urticaria remain areas of active research.
• Understanding the pathophysiology is crucial for developing effective treatments.

Observation:

• A patient presented with severe solar urticaria triggered by ultraviolet (UV) radiation wavelengths between 290-420 nm.
• Exposure led to rapid wheal formation, malaise, and syncope.
• In vitro irradiated plasma induced local whealing, suggesting a plasma-borne mediator.

Findings:

• Antihistamine treatment effectively inhibited UV-induced wheals.
• Lidocaine, hydrocortisone, substance P depletion, and a single PUVA treatment were ineffective.
• Repeated daily UVA irradiation with increasing doses normalized the patient's minimal urticarial dose (MUD).

Implications:

• This case suggests that phototherapy with controlled UVA exposure may be a viable treatment for solar urticaria.
• The findings highlight the role of plasma mediators in the pathogenesis of solar urticaria.
• Further research into phototherapy protocols could offer a novel therapeutic strategy for patients with this condition.