Pathogenesis and classification of solar urticaria: a new concept

Pathogenesis of solar urticaria: Classic perspectives and emerging concepts

Solar urticaria is a rare, immunologically mediated photodermatosis in which activation of cutaneous mast cells is triggered by specific wavelengths of solar electromagnetic radiation. This manifests clinically as the rapid development of cutaneous itch, erythema and wheal formation after several minutes of sun exposure. Disease mechanisms in solar urticaria remain incompletely elucidated and there have been few recent investigations of its pathobiology. Historic passive transfer experiments performed during the twentieth century provide support for a 'photoallergy' model of disease pathogenesis, wherein molecular alteration of a putative chromophore by solar electromagnetic radiation produces mast cell activation via an IgE-dependent mechanism. However, this model does not account for several observations made during passive transfer experiments nor does it explain a range of subsequent clinical and photobiological observations made in solar urticaria patients. Furthermore, increased understanding of the molecular dynamics underpinning cutaneous mast cell responses highlights the need to reformulate our understanding of solar urticaria pathogenesis in the context of this contemporary scientific landscape. In this review, we discuss the current understanding of solar urticaria pathogenesis and, by incorporating recent scientific and clinical observations, develop new hypotheses to drive future investigation into this intriguing disorder.

A Woman With Solar Urticaria and Heat Urticaria: A Unique Presentation of an Individual With Multiple Physical Urticarias

Urticaria is a common group of dermatologic disorders characterized by hives. Solar urticaria and heat urticaria are two rare types of chronic inducible urticarias. Solar urticaria is triggered by exposure to sunlight or ultraviolet radiation. Heat urticaria is triggered by exposure or contact with a heat stimulus. A 63-year-old woman is described who has both solar urticaria and heat urticaria and the features of these chronic inducible urticarias are reviewed. The woman presented with urticarial lesions that appeared both after exposure to the sun and after cooking at a stove. Additional history revealed she was previously diagnosed with diabetes, hypertension, and thyroid disease. After sun exposure, a punch biopsy of both the affected skin, as well as the normal-appearing skin, was done. Correlation of the clinical history, cutaneous examination, and biopsy examination confirmed the diagnosis of solar urticaria. Treatment of the patient's urticarias included histamine 1 (H1) and histamine 2 (H2) antihistamines. Her symptoms resolved and did not recur provided that she took the medication as prescribed. Management of chronic urticaria includes not only treatment of the current episode but also prevention of future recurring urticarial lesions. In addition to antihistamines, treatment may include omalizumab (Xolair®) injections for persistent urticaria.

Solar urticaria - An Australian case series of 83 patients

Solar urticaria (SU) is a rare form of urticaria with a pathogenesis that is poorly understood. It affects all skin types, can be difficult to diagnose, and is challenging to manage effectively. We conducted a retrospective review of patients with SU in our institution. A total of 83 patients (56 females) were identified as having SU. The mean age was 32 years (7-74) at first development of symptoms/signs of SU. Pruritus was the most common symptom reported (79%). Of the 60 patients who underwent monochromator testing at least once, 35 had SU confirmed with most reacting to visible light and UVA, or to UVA alone. Antihistamines and sun avoidance remain the mainstay treatment for SU but other treatments, including omalizumab, are of potential interest in treating patients with recalcitrant SU. The characterisation of this large case series of patients may help dermatologists recognise and manage this rare disorder appropriately.

Infrared radiation increases skin damage induced by other wavelengths in solar urticaria

BACKGROUND

Photodermatoses are typically investigated by analyzing the individual or combined effects of ultraviolet A (UVA), ultraviolet B (UVB), and visible light using light sources that simulate portions of the solar spectrum. Infrared radiation (IRR), however, accounts for 53% of incident solar radiation, but its effects are not taken into account in standard phototest protocols.

AIMS

The aim was to analyze the effects of IRR, alone and combined with UVA and visible light on solar urticaria lesions, with a distinction between infrared A (IRA) and infrared B (IRB).

METHODS

We performed standard phototests with UVA and visible light in four patients with solar urticaria and also tested the effects after blocking IRB with a water filter. To analyze the direct effect of IRR, we performed phototests with IRA and IRB.

RESULTS

Initial standard phototests that were all positive found the induction of erythema and whealing, while when IRR was blocked from the UVA and visible light sources, three of the patients developed no lesions, while the fourth developed a very small wheal.

CONCLUSION

These results suggest that IRR has the potential to produce and exacerbate lesions caused by other types of radiation. Consideration of these effects during phototesting could help prevent diagnostic errors.

Clinical and photobiological response in eight patients with solar urticaria under treatment with omalizumab, and review of the literature

BACKGROUND

Solar urticaria (SU) is a rare photodermatosis. Treatment is challenging, and outcomes are often disappointing. Omalizumab is an anti-IgE, currently approved for treatment of chronic spontaneous urticaria. We sought to evaluate therapy with omalizumab in refractory SU and describe predictive factors for response.

MATERIALS/METHODS

Patients with refractory SU under treatment with omalizumab were included in this study. Clinical outcome was evaluated using the Urticaria Activity Score 7 (UAS7), Dermatology Life Quality Index (DLQI) and Pruritus Visual Analogue Scale (VAS). Complete clinical response (CCR) was defined as having an UAS7 = 0, DLQI <6 and VAS = 0. Phototesting was performed and compared to baseline. We performed a PubMed search to identify reported cases of SU in adults treated with omalizumab, analysing their characteristics in order to predict response to omalizumab.

RESULTS

Eight patients were included. Median age was 45.5 years (range, 23-64). Light spectrum most commonly implicated was UV-A. Clinical outcomes: 89% (7/8) achieved CCR with omalizumab. Phototesting was normal in 42.8% (3/7) of them. In our review, we identified 38 patients (including the current case series), and 68.4% showed favourable outcomes with omalizumab. Median time since onset of SU was lower in responders.

CONCLUSIONS

Omalizumab can be an effective treatment in refractory SU.

Solar urticaria: Epidemiology and clinical phenotypes in a Spanish series of 224 patients

BACKGROUND

Solar urticaria is a chronic inducible urticaria also classified as an idiopathic dermatosis. The objective of this paper is to define the phenotypic characteristics of solar urticaria and to evaluate its incidence.

MATERIAL AND METHOD

This was a retrospective multicenter study in which data were gathered on the epidemiology and clinical, photobiologic, laboratory, and therapeutic characteristics of solar urticaria.

RESULTS

A total of 224 patients (141 women and 83 men) were included from 9 photobiology units. The mean age of the patients was 37.9 years (range, 3-73 years). A history of atopy was detected in 26.7%, and the most common presentation was allergic rhinitis (16.5%). Clinical signs were limited to sun-exposed areas in 75.9% of patients. The light spectrum most commonly implicated was visible light only (31.7%), and in 21% of cases it was only possible to trigger solar urticaria with natural light. The treatments most widely used by photobiology experts were oral antihistamines (65.46%), followed by different forms of phototherapy (34%). Complete resolution was observed most often in patients with solar urticaria triggered exclusively by visible or natural light, with statistically significant differences with respect to other wavelengths (P<.05). No increase in the annual incidence of solar urticaria was observed.

CONCLUSIONS

We have presented the largest series of solar urticaria published to date. The epidemiological, clinical, and photobiologic findings confirm previously reported data, although there was a particularly high rate of negative phototests in our series. Reactivity exclusively to visible or natural light was associated with a higher probability of resolution. No increasing trend was observed in the annual incidence.

Solar urticaria

Solar urticaria is a rare IgE-mediated and chromophore-dependent photodermatosis. In some cases, these chromophores, designated as "serum factor", may be detected in serum or plasma. To date, the exact pathogenesis of solar urticaria has, however, not been elucidated. Typical clinical features include the onset of urticarial lesions within a few minutes after light exposure, which already raises diagnostic suspicion. The most common triggers are UVA and visible light. Determination of the action spectrum as well as the minimal urticarial dose (MDU) is diagnostically crucial. Other photodermatoses such as polymorphic light eruption or porphyrias (especially erythropoietic protoporphyria) have to be ruled out. Apart from sunlight avoidance, which is always required, further therapeutic options used include nonsedating antihistamines as well as light hardening. Newer treatment modalities such as plasmapheresis or the anti-IgE antibody omalizumab are reserved for severe, recalcitrant forms of solar urticaria.

Solar urticaria in a 1-year-old infant: diagnosis and management

Solar urticaria is a type of inducible urticaria triggered by sun exposure resulting in hives on exposed skin as well as risk of developing systemic symptoms. Most cases are reported in the adult population. However, cases do occur in children. We present a case of visible light induced urticaria in a 12-month-old girl that demonstrates the need for accurate diagnosis and appropriate management.

Photosensitivity disorders in children: part I

Photosensitivity disorders in children encompass a diverse group of diseases. Compared to adult patients, underlying systemic disorders, including genetic or metabolic defects, are common causes in pediatric photosensitivity disorders. Photosensitivity in a child should be suspected if the child develops a sunburn reaction in sun-exposed sites after limited sun exposure. Diagnosis of a photodermatosis is made based on careful history taking and a physical examination. Early recognition and prompt diagnosis are essential to minimize long-term complications associated with inadequate photoprotection. In part I of this continuing medical education article, immunologically mediated photodermatoses, photodermatoses caused by exogenous photosensitizers, and the cutaneous porphyrias will be covered.

A review of UVA-mediated photosensitivity disorders

A number of skin conditions are characterised by photosensitivity to UVA. Some of these are exclusively UVA-mediated conditions, while others include UVA in the action spectrum which also include UVB and/or visible light. This review aims to describe this diverse range of conditions for non-dermatologist scientists with an interest in this topic. As such, clinical details, including treatments, are brief and succinct. Recent advances in understanding the pathogenesis of these conditions is highlighted.

Physical urticaria

Physical urticarias are a unique subgroup of chronic urticaria in which patients develop urticaria secondary to environmental stimuli. Common triggers include exercise, temperature changes, cold, heat, pressure, sunlight, vibration, and water. Systemic symptoms have occurred during severe episodes. Physical urticarias are responsible for approximately 20% to 30% of all cases of chronic urticaria. A basic knowledge of these unusual disorders is important for all healthcare providers. This article covers the following types of physical urticarias: dermatographism, cholinergic urticaria, local heat urticaria, exercise-induced anaphylaxis, vibratory angioedema, solar urticaria, and aquagenic urticaria.

Solar urticaria in Singapore: an uncommon photodermatosis seen in a tertiary dermatology center over a 10-year period

BACKGROUND

Solar urticaria is an uncommon photodermatosis, characterized by the appearance of pruritic wheals after sun exposure. In this study, we examine the photobiological characteristics of solar urticaria in the heterogeneous group of Singaporean patients.

METHODS

The photobiological features of all patients treated for solar urticaria at a tertiary dermatology center in Singapore over a 10-year period were retrospectively examined.

RESULTS

A total of 19 patients were diagnosed to have solar urticaria from 1993 to 2002. The mean age at diagnosis was 26 years, with a racial distribution of 17 (90%) Chinese, one (5%) Malay, and one (5%) Indian. Fifteen (79%) patients were males and four (21%) were females. The face/neck (47%) and arms/forearms (58%) were most often affected. Six (32%) patients had a history of atopy and two (11%) had dermographism. Fifteen (79%) patients had Fitzpatrick's skin type IV, three (16%) had skin type III and one (5%) patient had skin type V. The mean exposure time to wheal formation was 23 min. The action spectra of solar urticaria were visible light for 12 (63%) patients, ultraviolet (UV) A for one (5%), visible light and UVA for five (27%), and natural sunlight for one (5%) patient. All patients reported partial improvement with a combination of antihistamines and sunscreens as the main modality of treatment.

CONCLUSIONS

Our data suggest that solar urticaria is an uncommon photodermatosis and a rare form of urticaria. Wheals were mostly elicited by visible light and/or UVA. A combination of antihistamines and sunscreens provided a useful form of therapy for patients with solar urticaria.

Urticaria

Urticaria has been known as a disease since antiquity. However, in the last decades an increasing understanding of the mechanisms involved in its pathogenesis has shown the high heterogeneity of different urticaria subtypes. Clear distinction of the subtypes is required not only to choose the correct measures in diagnosis and management, but also to interpret the available data in research. The subtypes can be grouped into spontaneous urticaria, which includes acute urticaria and chronic urticaria, the physical urticarias, special types of urticaria including, e.g. contact urticaria, and diseases related to urticaria for historical reasons, e.g. urticaria pigmentosa. Most urticaria subtypes have a profound impact on the quality of life and effective treatment is thus required in case the diagnostic procedures do not reveal a cause which can be treated. Although, for symptomatic relief, nonsedating H1-antihistamines are the first choice in most subtypes of urticaria, double-blind controlled studies have shown that dosages required may exceed those recommended for other diseases, e.g. allergic rhinitis. Alternative treatments should be reserved for unresponsive patients.

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.

[Photodermatoses during childhood]

Actinic dermatitis and phototoxic and idiopathic photodermatoses occur relatively often during childhood. Photodermatoses stemming from enzyme defects and genetic disorders are much less common, while photoallergic and chronic actinic dermatitis have not been dealt with to date. A specific sensitivity of a child's skin to light is often the first manifest clinical symptom of a photodermatosis, the key is to ensure early diagnosis. However, it is often difficult to reach a diagnosis, as the lesions are barely perceptible or have even healed by the time the patient is examined. This is why photoprovocation tests are so important in diagnosing photodermatoses, particularly during childhood. In addition to early diagnosis of these illnesses and offering the appropriate treatment, it is also crucial that the parents be well informed and aware of what symptoms to look for so that they can protect their children from overexposure to UV light and thereby avoid later actinic injuries that can become as serious as malignancies.

Successful treatment of solar urticaria by extracorporeal photochemotherapy (photopheresis)--a case report

Solar urticaria is characterized by erythema and whealing immediately after exposure to ultraviolet radiation and/or visible light. We report about a patient with severe solar urticaria, who was highly sensitive to both UVA radiation and visible light with a Minimal Urticaria Dose (MUD) of 7 J/cm2 UVA. Management of this patient was extremely difficult because standard treatment with oral antihistamines, hardening with UVA, UVB, visible light or oral PUVA and even oral cyclosporin A were completely ineffective. We therefore decided to perform extracorporeal photochemotherapy (photopheresis, ECP). After nine treatment cycles with photopheresis the MUD increased from 7 J/cm2 UVA before treatment to 22 J/cm2 UVA. This hardening effect was associated with a significant decrease of the frequency and severity of whealing and the accompanying symptoms (pain, fatigue, pruritus).

CONCLUSION

Photopheresis might be of some benefit in selected patients with otherwise intractable solar urticaria.

Idiopathic photodermatoses: clinical, diagnostic and therapeutic aspects

Idiopathic photodermatoses are a group of photosensitivity dermatoses, which are not very frequent with the exception of polymorphous light eruption. Therefore, their recognition may not be easy for dermatologists who are not familiar with photosensitivity diseases.

LEARNING OBJECTIVE

The information in this review is intended for giving clinical, diagnostic and therapeutic clues for the correct management of patients. Clinical features will be described together with diagnostic relevant procedures and usual therapeutic measures.

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.

Oxidative stress in physical urticarias

The pathogenesis of the physical urticarias has not been completely defined. Indeed, different stimuli can induce similar clinical manifestations, some of which are capable of generating reactive oxygen species. In order to evaluate whether the generation of an oxidative stress response could be a common pathogenetic mechanism of the disease, we have determined the profile of a number of chemical and enzymatic antioxidants in blood samples from a group of patients with physical urticarias. Compared with controls, a systemic imbalance of the antioxidants was detected in the patient group with a decrease of both plasma vitamin E and cellular catalase and glutathione peroxidase activities along with an increase of superoxide dismutase activity. Moreover, an increase in the percentage of plasma polyunsaturated fatty acids, as a target for peroxidative damage, was also observed. These alterations may lead to an increased percentage of peroxidable compounds in skin and to the intracellular generation of reactive oxygen species and could therefore provide one possible explanation for the patients' urticarial response to stimuli. Even if the alteration of the antioxidant status is secondary to changes in cytokine or complement activation, our results suggest a common biochemical profile in patients with different forms of physical urticaria.

Drug-induced solar urticaria due to tetracycline

Solar urticaria is an uncommon disorder characterized by pruritus, erythema and whealing commencing within minutes of exposure to ultraviolet (UV) and visible light, and generally resolves in a few hours. We describe a 28-year-old woman who developed pruritus and erythema 5 min after sun exposure while on tetracycline for treatment of perioral dermatitis. Phototesting elicited urticarial reactions in the UVA, UVB and visible spectra. Repeat phototesting after cessation of tetracycline was negative. This report documents the first case of solar urticaria induced by tetracycline.

The clinical presentations of urticaria

Urticaria is a common skin condition. Although an episode may be mild and last only a few days, chronic urticaria can significantly affect the quality of life. The condition is frequently misunderstood by patients who believe the condition is always the result of an allergy and is dangerous.

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.

The idiopathic photodermatoses

The idiopathic photodermatoses present a challenge for dermatologists. Although, as in other specialty areas, the classical clinical presentation produces few problems, it is the severe forms and overlap cases that cause the most difficulty. It is fortunate that the semi-objective investigation of phototesting is available, which, when conducted carefully, reveals so much about the nature of this group of conditions. This essential investigation not only helps achieve a diagnosis, but also affords material for study and a means of monitoring therapy response or progress towards spontaneous resolution. Although these conditions are grouped together, throughout this century we have seen a continuing process of distinct diseases emerging as a consequence of careful clinical observation and investigation.

Treatment of refractory solar urticaria with plasma exchange

BACKGROUND

Solar urticaria is a photodermatosis that can be very disabling for patients who are highly sensitive to light and can also be very resistant to therapy.

OBJECTIVE

To correlate the results of serial phototesting in a patient with severe and refractory solar urticaria before and after treatment with plasma exchange.

METHODS

Plasma exchange was performed five times over a period of 10 days. Phototesting to ultraviolet A (UVA) irradiation and visible light was performed with fluorescent ultraviolet tubes and an incandescent lamp.

RESULTS

The urticaria that developed after very low light doses during baseline phototesting could not be provoked following plasma exchange. The patient is now almost symptom-free, with only occasional and transient hives more than 21 months after her last plasma exchange.

CONCLUSIONS

Plasma exchange is a therapeutic modality to consider in highly light-sensitive patients when other treatments have failed.