Photopatch testing

Photopatch testing in Bogota (Colombia): 2011-2013

BACKGROUND

Photopatch tests are used to diagnose photoallergic contact dermatitis and identify the causal agents. The frequencies of positive results and associated allergens vary by country; therefore, it is necessary to know the information specific to each country.

OBJECTIVE

To establish the frequency of positive photopatch test results, and their relevance, in patients with suspected photoallergic contact dermatitis in a national dermatology centre located in Bogota, Colombia.

MATERIALS AND METHODS

One hundred patients investigated for possible photoallergic contact dermatitis were enrolled in the study. They were photopatch tested with a selected group of allergens, and occluded for 48 hours; the duplicate right-hand panel was irradiated with 5 J/cm(2) ultraviolet (UV)A. The readings were performed on day (D)2, D4, and D6, in accordance with the guidelines of the ICDRG, and the relevance was evaluated with the COADEX system.

RESULTS

There were a total of 20 photopatch reactions in 15 patients, 95% of which were caused by UV filters, most frequently benzophenone-3 (55%). Eight of the positive reactions (53.3%) appeared on D6.

CONCLUSIONS

UV filters continue to be the most common causes of photoallergic contact dermatitis in our patients. Readings up to D6 (96 h after irradiation) are important to identify delayed positive reactions.

Causal agents of photoallergic contact dermatitis diagnosed in the national institute of dermatology of Colombia

OBJECTIVE

To describe and identify the photoallergens causing photoallergic contact dermatitis in the population attending the outpatient clinic of the Centro Dermatologico Federico Lleras Acosta (CDFLLA), the National Institute of Dermatology of Colombia.

MATERIALS AND METHODS

Eighty-two patients with clinical diagnosis of photoallergic contact dermatitis enter the study. These patients attended the CDFLLA between August 2001 and May 2003. Photopatch tests were performed using the standard series of sunscreens (Chemotechnique Diagnostics) and 6-methylcoumarin. Cetyl alcohol, phenoxyethanol, methylparabene, propylene glycol, triethanolamine, propylparabene, trichlorocarbanilide and dichromate were also included. The allergens were applied in duplicate on the healthy skin of the back and covered with opaque tape withdrawn 24 h later, the panel on the right was irradiated with an ultraviolet A dose of 5 J/cm(2). The tests were read 24 h after the application of the allergens, 24 and 72 h post-irradiation. The readings were assessed according to the visual scoring system recommended by the International Contact Dermatitis Research Group.

RESULTS

Twenty-six patients (31.7%) showed positive photopatch test responses to one or several allergens. Four of them showed positive results to three components of the series and four patients to two components. Thirty-eight photoallergic and 18 allergic reactions were observed. Ultraviolet filters were the substances which more frequently produced positive photopatch test responses (30.5%). The most common ultraviolet filter photoallergen was benzophenone-3 with 22/82 positive results (26.8%), followed by octyl methoxycinnamate (8/82), benzophenone-4 and mexenone (2/82), phenylbenzimidazole sulphonic acid, methylbenziliden camphor and octyl dimethyl PABA (1/82). One patient showed a photoallergic response to 6-methylcoumarin. There was a concordance between the allergen which elicited the positive response and the use of different substances which contained that molecule among its compounds in 17 patients (65.3%). 19.5% of the patients (16/82) showed positive results to one or several allergens in the irradiated panel as well as in the unirradiated control site. These cases were diagnosed as contact allergy, probably caused by aeroallergens, presenting a natural history and a clinical picture similar to photocontact allergy. The most common allergen was dichromate with 10 positive results.

CONCLUSIONS

The results of this study confirm that sunscreens are the more frequently involved substances in photoallergic contact dermatitis in our population. Identification of the photoallergen is the key element for adequate disease control and patient education.

Classification and evaluation of photodermatoses

Photodermatoses can be classified into five general categories: 1) idiopathic photodermatoses, including polymorphic light eruption (PMLE), actinic prurigo, hyroa vacciniforme, chronic actinic dermatitis, and solar urticaria; 2) photodermatoses which are secondary to exogenous agents, including phototoxic and photoallergic reactions; 3) photodermatoses secondary to endogenous agents, mainly the porphyrias; 4) photoexacerbated dermatoses, including autoimmune disease, infectious conditions, and nutritional deficiencies; and 5) genodermatoses. The initial step in evaluating a photosensitive patient is based on a directed personal and family history. The morphology of the eruption, phototests, and in some patients, photopatch tests are essential in focusing the diagnosis. Skin biopsies and laboratory investigations, such as antinuclear antibody (ANA) panels and porphyrin profiles, may be required to further confirm the diagnosis.