In solar urticaria, following sun exposure, a cutaneous or circulating photo allergen produces an allergic response in the form of itchy red hives on the skin. Though a rare skin disease, this can potentially be a debilitating and serious problem for the affected individuals.
Causes of Solar Urticaria
The exact cause of solar urticaria is unknown. Mast cell degranulation with release of histamine secondary to solar irradiation is seen in patients. Passive transfer of solar urticaria to normal individuals following injection of serum from patients has been reported. A wide range of light spectrum including the visible light, UVA, UVB and even infrared has been shown to produce the allergic wheals in solar urticaria.
Horio and Minami, in a February 1977 article titled "Photo allergens in a Patient's Serum" in Archives of Dermatology, postulated that a pigment containing substance called chromophore, present in the serum or the dermis of patients, gets activated by light and converts into an immunologically active photo allergen. This photo allergen then causes mast cell degranulation following light exposure. Kojima et al, in 1986, in an article named "Solar Urticaria- the Relationship of Photo allergen and Action Spectrum" in Archives of Dermatology, subsequently hypothesized that photo allergens of different molecular weights were responsible for the varied reactivity to the light spectrum in patients with solar urticaria.
Urticarial rashes following sun exposure can also be caused by some drugs like benoxaprofen, chlorpromazine, oral contraceptive pills, topical tar preparations and endogenous metabolites produced in diseases like erythropoietic protoporphyria, porphyria cutanea tarda and systemic lupus erythromatosus.
Clinical Features and Diagnosis of Solar Urticaria
Clinically, lesions appear within 1-30 minutes of solar exposure, and may last from 15 minutes to 3 hours. Presentation is usually with itchy wheals and a morbiliform erythematous rash. Common sites affected are face, V area of the neck and the forearms, dorsum of hands and arms. Systemic symptoms like giddiness, headache, wheezing, fainting, and, rarely, life threatening anaphylactic shock can also occur in severe cases.
In a different type of solar urticaria, known as fixed solar urticaria, itchy red hives appear on specific body areas after light exposure.
Photo testing usually clinches the diagnosis in solar urticaria. Different light sources for UVA, UVB, visible light, sunlight and infrared rays are used to find out the exact type of radiation producing the solar urticaria. Blood tests to rule out other causes of sun induced urticaria is also mandatory before diagnosing solar urticaria.
Treatment of Solar Urticaria
The treatment of Solar Urticaria is difficult and time consuming in most affected individuals.
- General Measures in the Treatment of Solar Urticaria: The primary level of treatment consists of sun avoidance or the use of physical barriers like sunscreens The sunscreens should contain both physical and chemical agents to cover the whole spectrum of light. Patients should wear thick cotton full sleeve shirts and preferably wear a long hat as well. It is advisable to use a pair of cotton gloves while driving. However, these measures are effective only in mild cases.
- Specific Measures in Solar Urticaria Treatment: Both H1 and H2 antihistamines are disappointing in the treatment of Solar Urticaria. Other drugs likeindomethacin, oral beta-carotene, oral steroids and antimalarial drugs yield varying results. Induction of tolerance to sunlight by repeated doses of sunlight exposure, PUVA or other artificial light sources is the only satisfying treatment available for solar urticaria at present. UVA rush hardening proposed by Stephan Beissert et al. is a safe and effective prophylactic treatment providing protection as early as 3 days in patients with UVA induced solar urticaria. In severe cases where other treatments have failed, solar urticaria has been successfully treated withcyclosporine A in a dose of 4.5-mg/kg-body weight per day. This is a potentially toxic drug and has to be reserved for the most severe and debilitating cases. Supportive Therapy withantioxidants is worth a trial in non responsive cases.
Related Article
Source
- Botto NC,Warshow EM. Solar Urticaria. J Am Acad Dermatol 2008;59:909-20
Disclaimer The information given in this article is for educational purpose only so that patients are aware of the options available. No diagnosis should be made or treatment undertaken without first consulting your doctor. If you do so, the author or suite101 will not be responsible for any consequences. The images provided are for illustration purpose only.
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