Practice Essentials
Solar urticaria is a rare, IgE-mediated, 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. (See Presentation.)
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. The condition can be quite disabling and difficult to manage. It often has a sudden, dramatic onset, and little information is available regarding its duration and eventual outcome. (See Presentation, DDx, Treatment, and Medication.)
See the images below.
Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria.jpg).
Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria1.jpg).
Diagnostics
Phototesting confirms the diagnosis, identifies the action spectrum, and establishes baseline data (eg, minimum urticarial dose [MUD]) for possible therapeutic interventions and monitoring in the future.
Treatment
Treatment of solar urticaria can be frustrating. A combination of different modalities is often necessary, but the success of these methods is highly variable. Taking measures to avoid or minimize sun exposure is the most important step for patients with solar urticaria. Unfortunately, this often requires major adjustments in lifestyle, which might be impractical for some patients.
Prognosis
Solar urticaria is usually a chronic condition; few patients experience spontaneous remission. Continued intake of oral antihistamines may prevent the whealing to a degree, thus allowing some tolerance to sunlight. Significant and more long-lasting improvement is observed in patients who undergo phototherapy or photochemotherapy. Some patients find that following preventive measures makes their condition manageable.
In some cases, skin eruption is accompanied by symptoms such as headache, nausea, vomiting, bronchospasm, and syncope. The mortality rate for solar urticaria has not been determined.
Patient education
Educate patients that, despite its persistent and chronic nature, solar urticaria is a benign disorder that is usually localized to the skin without affecting general health. Emphasize that response to treatment is generally unpredictable and that prevention by avoidance may ultimately be the key to the management of this condition.
Epidemiology
Solar urticaria accounts for only 4% of patients in the United States with photosensitive disorders and, worlwide, for 0.5% of all urticaria cases and 7% of photodermatoses. [1]
The disorder has been reported in all skin types and ethnic groups, worldwide, with a slight female predilection. Regarding age, the disease has a wide range of onset (10-70 years). Typical onset is 20-40 years. [2] The mean age of onset for solar urticaria is 35 years, but it has been reported to occur in infancy. [3, 4, 1]
Solar urticaria is associated with other types of chronic urticaria in up to 16% of patients. [1] For example, there is a case recorded of a 63-year-old woman with simultaneous solar urticaria and heat urticaria. [5]
Etiology
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:
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Type I - This type is characterized by an immunoglobulin E (IgE)–mediated hypersensitivity to specific photoallergens generated only in solar urticaria patients
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Type II - This type is characterized by an IgE-mediated hypersensitivity to nonspecific photoallergens found in solar urticaria patients and in 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 solar urticaria may be related to the specific photoallergen and its molecular weight. Diversity in the reported action spectra for the disease 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. [6]
In a longitudinal study of 27 solar urticaria patients, investigators determined the action spectrum for 44% of patients to be UVB, 70% to be UVA, 89% to be UVA-1, 37% to be green light, and 22% to be red light. [7] In a limited study of only 11 solar urticaria cases, Uetsu et al found augmentation spectra to be UVB in 3 cases (27.3%), UVA in 2 cases (18.2%), visible light in 4 cases (36.4%), UVA and UVB in 1 case (9.1%), and UVA and visible light in 1 case (9.1%). [8]
Complex interactions occur between the various wavelengths and the photoallergen. [9]
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. [10]
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Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria.jpg).
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Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria1.jpg).
