Background
Solar urticaria is a rare photodermatosis characterized by pruritus, stinging, erythema, and wheal formation after a brief period of exposure to natural sunlight or an artificial light source emitting the appropriate wavelength.
Initially described by Merklen in 1904, solar urticaria is localized to exposed areas of the skin, although it can occur through thin clothing. Solar urticaria disappears within several minutes to a few hours, without pigmentary change if further sun exposure is avoided. Solar urticaria can be quite disabling and difficult to manage. Solar urticaria often has a sudden, dramatic onset, and little information is available regarding its duration and eventual outcome.
Pathophysiology
Solar urticaria is possibly caused by an antigen-antibody reaction. Solar irradiation may induce an antigen in the serum or plasma of affected individuals. Intradermal injection of serum from a solar urticaria patient passively, but not consistently, transfers the condition to a healthy individual.
The following types of solar urticaria have been proposed:
- Type I: This type is an immunoglobulin E (IgE)–mediated hypersensitivity to specific photoallergens generated only in solar urticaria patients.
- Type II: This type is an IgE-mediated hypersensitivity to nonspecific photoallergens found in both solar urticaria patients and healthy individuals.
Passive transfer test findings are positive in patients with type II solar urticaria, but they may be positive or negative in those with type I.
The wide action spectrum (290-800 nm) implicated for this condition may be related to the specific photoallergen and its molecular weight. Diversity in the reported action spectra may be due to differences in photoallergens. In addition, spectra believed to be responsible for either inhibition or augmentation of the reaction have been detected. Complex interactions occur between the various wavelengths and the photoallergen.[1]
The result of these interactions is mast cell degranulation with subsequent histamine release. Mediators other than histamines may also be involved. Inhibition of solar urticaria with light suppresses the wheal-flare response following intradermal injection of photoactivated autologous serum but does not suppress the wheal and flare associated with compound 48/80.[2]
Epidemiology
Frequency
United States
Solar urticaria comprises only 4% of US patients with photosensitive disorders.
International
Solar urticaria comprises 5.3% of the cases of photosensitive dermatoses worldwide.
Mortality/Morbidity
The mortality rate for solar urticaria has not been determined. In some cases, skin eruption is accompanied by symptoms such as headache, nausea, vomiting, bronchospasm, and syncope.
Race
Solar urticaria occurs in all races.
Sex
A slight female predilection is noted for solar urticaria.
Age
Solar urticaria has a wide range of onset (10-70 y). The mean age of onset for solar urticaria is 35 years, but it has been reported to occur in infancy.[3]
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