Drug photoallergy

Photoallergy

Abstract Photoallergic contact dermatitis (PACD) is a hypersensitivity reaction mounting from skin exposure to generally harmless amounts of ultraviolet and/or visible light in the presence of a photoreactive allergen. These reactions are typically delayed type (Gell and Coombs type IV) reactions and require pre-sensitization to photoallergens. Phototoxic reactions are clinically similar and often difficult to differentiate from photoallergies, but they are caused by interaction of light with photoirritants and do not require sensitization. The main investigative technique to diagnose PACD is photopatch testing, which is not commonly used; therefore, PACD may be overlooked in many patients. Currently, leading contact photosensitizers are sunscreens and topical non-steroidal anti-inflammatory drugs. This article provides an overview on photocontact allergies.

Drug-induced photoallergic and phototoxic reactions

Drug-induced photosensitivity involves reactions to medication triggered by exposure of the skin to ultraviolet light. Medications that trigger reactions can be topical or oral. Following interaction of ultraviolet radiation with a chemical present in sufficient amounts in the skin, one of the several reactions may occur in susceptible patients, most commonly photoallergy or phototoxicity. These reactions can be diagnosed separately based on pathogenesis, clinical characteristics and histopathology. Phototoxic disorders have a higher incidence than photoallergic disorders. The action spectra for most photoallergens and phototoxins lie in the ultraviolet A range. Subtypes of drug-induced photosensitivity include dyschromia, pseudoporphyria, photo onycholysis, and lichenoid and telangiectatic reactions.

Photosensitivity associated with treatment with triflusal

BACKGROUND

Triflusal is a fluorinated aspirin derivative with antiplatelet properties, which is used in Spain for the management and prevention of thromboembolic disease.

CASE REPORT

A 91-year-old female developed a systemic photosensitivity reaction 15 days after beginning triflusal preventive treatment (300 mg/12 h) for prior transient ischaemic attack. Photobiological study showed an abnormal response to light in areas exposed to ultraviolet B and A radiation, with a photopatch test positive to both triflusal and its main metabolite. These observations suggested a causal relation between triflusal and the clinical findings, as described in previous reports.

CONCLUSIONS

The few cases reported to date and the clinicopathological features of this case suggested an immunological response as the most likely cause of the reaction.

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.

Quinidine-induced photodermatitis confirmed by photopatch testing

A patient with quinidine-induced photosensitivity confirmed by photopatch testing is presented. The action spectrum for the reaction appeared to be in the UVA range, and the patient's minimal erythema dose was lower than expected while the patient was on quinidine.

Phototoxicity and photoallergy in man

Photosensitivity is the broad term used to denote adverse reactions to the sun. These reactions may be phototoxic or photoallergic. Phototoxic reactions are much more common than photoallergic reactions. Phototoxic reactions may be photodynamic or nonphotodynamic in nature, the primary difference being that photodynamic reactions require oxygen. Porphyrins are examples of molecules which produce photodynamic responses. The 8-methoxypsoralen photobinding to DNA is an example of a nonphotodynamic reaction. The UVB sunburn response is the most common phototoxic reaction, and it appears to be nonphotodynamic in nature. Photoallergy is uncommon. As with all allergies it is an acquired, altered reactivity dependent on an antigen-antibody or cell-mediated hypersensitivity response. Solar urticaria due to UVB rays is an example of a circulating antibody-dependent reaction, and allergic photocontact dermatitis induced by the halogenated salicylanilides is an example of a cell-mediated response. The mechanisms of these reactions are discussed.

Polymorphous light eruption

A review of the available information indicates that the polymorphous light eruptions are characterized by a number of clinical and histologic features. The clinical patterns range from multiple small papules and papulovesicles, which become confluent, to large plaques. The former usually involve all of the sun-exposed areas and the latter frequently are localized to the face. Histologically, the epidermal changes vary with the clinical presentation. However, a perivascular round cell infiltrate in the dermis is present in all of the lesions. The disease has a worldwide distribution, though there is a high incidence in certain populations such as North and Latin American Indians and Finnish people. The disease usually begins in young adult life except in the American Indian population, where it tends to start in childhood. Though in several series there was a preponderance of females, males do develop the problem in significant numbers. The action spectrum falls primarily in the ultraviolet B (UVB) range. Some patients do react to ultraviolet A (UVA) rays as well. However, there is evidence that the process is not confined to any narrow band of radiation, but can be produced by any wavelength or energy source as long as one uses sufficient exposure dose to produce a delayed phototoxic erythema. Pathogenetically, it is likely that polymorphous light eruption (PMLE) actually includes more than one disease entity. Whether photoallergy plays a role in any of these responses remains to be seen. In addition, the relationship to the persistent light reactor, photosensitive eczema, and actinic reticuloid has not been clarified at this time.