Solar urticaria inhibited by visible light

Narrowband ultraviolet B phototherapy is a suitable treatment option for solar urticaria

BACKGROUND

Narrowband (NB) ultraviolet (UV) B lamps are widely used for treatment and prophylaxis of several skin diseases.

OBJECTIVE

We sought to assess the efficacy of two protocols of NB-UVB therapy for the prophylaxis of UVB-sensitive and UVB-insensitive solar urticaria (SU).

METHODS

Subjects affected by SU underwent phototesting for assessment of the minimal erythemal dose and minimal urticarial dose. Patients without urticarial response to UVB underwent a single daily exposure every other day for 4 weeks (group A). Patients with a urticarial test response to broadband UVB or NB-UVB (group B) received 3 daily exposures (on working days) for the first week. Afterward, they were treated as the patients of group A for 3 weeks. Follow-up visits took place after 1 and 3 months.

RESULTS

A total of 39 patients completed the study. In groups A (29 patients) and B (10 patients), the median total number of exposures was 12 (interquartile range [IQR]: 12; 15) and 25.5 (IQR 24; 27), respectively. The median total NB-UVB dose was 10.3 J/cm(2) (IQR 9.9; 11) for group A and 9.1 J/cm(2) (IQR 8.5; 10.6) for group B. At follow-up visits, patients reported good tolerance to the sun.

LIMITATIONS

A direct comparison of NB-UVB with UVA or psoralen plus UVA for the photoprophylaxis of SU is still lacking.

CONCLUSION

NB-UVB phototherapy was well-tolerated and effectively prevented SU relapses.

Diagnosis and treatment of solar urticaria

Solar urticaria is one of the most annoying of the photodermatoses. It can be difficult to diagnosis because of phototesting problems, and it is not easy to treat. The different treatment modalities available all have their practical problems, so it is difficult to provide the patient with adequate protection. In many patients, however, treatment can reduce the symptoms and allow regular exposure of the skin to natural sunlight as the skin becomes more tolerant to the provoking wavelengths, the result being more complete protection.

Mechanisms of phototherapy and photochemotherapy for photodermatoses

Most photodermatoses represent indications for preventive ultraviolet (UV) phototherapy and/or psoralen plus ultraviolet A (PUVA) photochemotherapy. The aim of treatment is to prevent the outbreak of disease by increasing the patient's tolerance to sunlight. The mechanisms by which ultraviolet B (UVB) and PUVA induce such tolerance are not completely understood. Pigmentation and skin thickening may be important factors in the protective effect, but they cannot sufficiently explain the degree of protection induced. Other mechanisms that may be of critical importance for the therapeutic efficacy encompass a variety of immunomodulatory effects on human skin known to be induced by UVA, UVB, and PUVA. Obviously the mechanisms of prophylactic phototherapy are strongly intertwined with the pathogenesis of the photodermatoses. The possible mechanisms of photoprevention are discussed for polymorphic light eruption (PMLE), actinic prurigo, chronic actinic dermatitis, and solar urticaria.

Pathomechanisms in physical urticaria

Various exogenous stimuli, e.g., rubbing, pressure, cold, heat, or electromagnetic waves, have been described to elicit whealing reactions, the so-called physical urticarias. They may occur as isolated diseases or in association with other types of urticaria. In many cases, the respective physical factors can be defined exactly, e.g., the degree of temperature changes or the range of eliciting ultraviolet wavelengths. In contrast, the underlying pathomechanisms are mostly still obscure. In the past, often contradictory results have been reported regarding the role of IgE, complement factors, histamine, or even mast cells. Recently, many investigations have been performed on solar urticaria where subgroups of patients with different clinical and pathophysiologic features could be defined and mechanisms of tolerance induction have been studied that also offered an efficient treatment modality. Therefore this review will mainly focus on this type of disease as a paradigm of the pathomechanisms of physical urticaria.

Phototoxicity and photoallergy

Photosensitivity may be phototoxic or photoallergic. Phototoxicity is much more common. There are 2 types of phototoxicity: photodynamic, which requires oxygen, and nonphotodynamic, which does not. Reactions induced by porphyrin molecules, coal tar derivatives, and many drugs are photodynamic. The reaction induced by psoralens, for the most part, is nonphotodynamic. Acute phototoxic reactions are characterized by erythema and edema followed by hyperpigmentation. Long-term ultraviolet phototoxicity results in chronic sun damage and skin cancer formation. Also, certain chemicals such as psoralen molecules and coal tar are photocarcinogenic. Phototoxic reactions to certain drugs produce unusual clinical patterns, that is lichenoid eruptions, dyschromia, photo-onycholysis, and pseudoporphyria. Photoallergy is an uncommon acquired altered reactivity dependent on an immediate antibody or a delayed cell mediated reaction. Solar urticaria is an example of the former, whereas photoallergy to exogenous chemicals is an example of the latter. Photoallergy to systemic drugs does occur but is difficult to characterize. The action spectrum for photoreactions to exogenous agents usually at least includes the ultraviolet A rays for both phototoxicity and photoallergy.

Solar urticaria induced by UVA and inhibited by visible light

An 18-year-old woman developed urticaria approximately 10 minutes after exposure to sunlight. The action spectrum was in the UVA range. Simultaneous irradiation of the skin with UVA and visible light wavelengths shorter than 460 nm induced wheals approximately 10 minutes after the end of the exposure, no matter how long the exposure time. Urticaria induced by UVA radiation was completely inhibited by immediate reirradiation of test sites with visible light wavelengths shorter than 460 nm. Visible light irradiation before exposure to eliciting wavelengths revealed no inhibitory effect, nor was an inhibitory effect found by pre- or postirradiation of test sites with visible light wavelengths longer than 530 nm. These findings suggest that the inactivation of a photoproduct or some subsequent step involved in the pathogenesis of the urticarial reaction was inhibited by visible light wavelengths shorter than 460 nm but not by visible light wavelengths longer than 530 nm.

Inhibition spectra of solar urticaria: a case report and a review of the Japanese cases

A 34-year-old Japanese female with solar urticaria is described, who had an episode of urticarial response when she was exposed to indoor fluorescent light first and sunlight later. The action spectrum was found to range from 480 to 520 nm with an inhibition spectrum above 650 nm in the visible light by both postirradiation and preirradiation. Injection of in vitro-irradiated serum did not produce an urticarial wheal on the patient. In the Japanese literature, 17 cases of solar urticaria with inhibition spectra have been reported. The wavelength of the inhibition spectrum was longer than that of the action spectrum in each case.

Pathogenesis and classification of solar urticaria: a new concept

Although its exact mechanism remains unknown, evidence supports the immunologic nature of solar urticaria. On the basis of experimental findings in the literature and our own observations, a new concept of the pathogenesis and classification of solar urticaria is presented. We propose two types of solar urticaria: type I, IgE-mediated hypersensitivity to specific photoallergens, which are generated only in patients with solar urticaria, and type II, induction of IgE-mediated hypersensitivity to a nonspecific photoallergen, which is generated both in patients with solar urticaria and in normal persons.

Augmentation spectrum in solar urticaria

A 24-year-old woman had solar urticaria that was activated by wavelengths ranging from 320 to 420 nm, mainly ultraviolet A light. The irradiation of visible light before exposure to activating wavelengths significantly enhanced an urticarial reaction in an augmentative but not in an additive fashion. The examinations using a monochromator revealed that the augmentation spectrum ranged from 450 to 500 nm. Postirradiation of the spectrum had no effect. The inhibition spectrum was also determined in longer wavelengths ranging from 550 to 600 nm. Both postirradiation and preirradiation of the inhibition spectrum exerted their effects. The augmentation spectrum revealed no effects on the wheal formation induced by histamine or compound 48/80 in the patient. The existence of augmentation spectrum has never been reported in solar urticaria, although the inhibition spectrum has been described by several authors.

A case of porphyria cutanea tarda with experimental light urticaria

Photobiological tests were carried out on a 32-year-old man who suffered from porphyria cutanea tarda (PCT). The patient developed an immediate type of skin reaction with erythema and whealing following monochromatic irradiation at 400 nm, but did not have any abnormal immediate skin reaction after exposure to natural sunlight. Pre- or simultaneous irradiation with visible light, wavelength greater than 650 nm, suppressed the development of urticaria induced by 400 nm monochromatic radiation. On the basis of these findings and our previous observation of an inhibitory spectrum in two cases of solar urticaria, we suggest that there is also an inhibitory spectrum in PCT. This could explain the extremely low incidence of immediate erythematous or urticarial reactions in sun-exposed skin in these patients.

Production and inhibition of solar urticaria by visible light exposure

The mechanisms of production and inhibition of solar urticaria were investigated in two patients whose eruptions were induced by wavelengths ranging from approximately 400 to 500 nm. They developed urticarial reactions to their own sera, which had been exposed previously to light in vitro. The exposure of skin to light from which activating wavelengths were eliminated with a glass filter (O-55), immediately after the exposure to urticaria-eliciting light, significantly inhibited the development of urticaria. The irradiation with the filtered light prior to the exposure of urticaria-eliciting light revealed no inhibitory effect. The simultaneous exposure of action and inhibition spectra seemed to suppress urticaria formation. The exposure of the inhibition spectrum did not affect wheal formation produced by histamine and a histamine-releasing agent. The photosensitizer produced by the action spectrum may be inactivated by the inhibition spectrum, or the interaction between photosensitizer and antibody may be blocked by the irradiation with the inhibition spectrum.