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On-line version ISSN 1678-4782
J. Pediatr. (Rio J.) vol.83 no.4 Porto Alegre July/Aug. 2007
LETTERS TO THE EDITOR
The review article by Ferreira et al.1 is an appropriate tool for a better understanding on food allergies (FA), a difficult theme for patients and physicians, particularly pediatricians working in front line care.
The difficulties involved in diagnosis of cell-mediated FA are a problem for patient management. Oral challenge tests are complicated to carry out, because the symptoms may occur over the long time in cell-mediated hypersensitivity, which makes it very difficult to perform oral double-blind placebo challenges and could be a major confounding factor for dietary diaries. Although the authors mention that cutaneous contact tests, also known as atopy patch tests (APT), have low accuracy, atopic dermatitis and eosinophilic esophagitis are diseases in which these tests may be helpful in the diagnosis and treatment of patients.
Recently, the European Academy of Allergology and Clinical Immunology (EAACI) published a position paper related to aeroallergens and food atopy patch tests, in response to the large number of articles that have been published on the subject. That review concluded that for atopic dermatitis patients that do not respond adequately to initial treatment with skin moisturizing, emollients and taking care with irritants, a combination of skin prick tests (SPT) or specific IgE for foods and APT can be helpful in the diagnosis of food allergies associated with eczema.2 The same article recommends the use of in natura foods while extracts are not yet standardized.2
In relation to eosinophilic esophagitis, particularly during childhood, there is a high level of association with FA. Patients develop an inflammatory process of the esophageal mucosa with the presence of eosinophils, 20 or more per high power field in biopsy of the lower third of esophagus. To control the inflammatory process, oral or swallowed corticosteroids are used together with exclusion of the food involved. In the absence of implicated foods it is necessary to make use of hydrolyzed proteins to control the inflammation.
Spergel et al.3-5 have recently demonstrated, in a series of articles undertaken with appropriate methodology, that combining APT with SPT or specific IgE for foods increases the positive predictive value of the allergy tests, thereby achieving a greater number of FA diagnoses, and, consequently, a reduction in the use of hydrolyzed proteins due to exclusion of specific foods, improving patient quality of life by reducing their costs.
There is a small number of studies on the utility of APT for other conditions associated with cell-mediated FA. Recently, Fogg et al. described, in a pilot study, 16 cases of eosinophilic proctocolitis in babies with clinical diagnoses confirmed by APT.
Atopy patch tests employed in conjunction with specific IgE assays or SPT can be helpful in the diagnosis and treatment of patients with FA due to mixed mechanisms and, possibly, for exclusively cell-mediated. There is a need for larger studies in order to investigate what the best formulations might be for APTs, whether in natura or using protein extracts and, what is the best diluent, whether saline, water or petroleum derivatives, such as petrolatum. Despite this, the use of these tests has a growing basis in the literature and, furthermore, the EAACI's position is in favor of their use in these pathologies and in specific cases.
1. Ferreira CT, Seidman E. Food allergy: a practical update from the gastroenterological viewpoint. J Pediatr (Rio J). 2007;83:7-20.
2. Turjanmaa K, Darsow U, Niggemann B, Rance F, Vanto T, Werfel T. EAACI/GA2LEN position paper: present status of the atopy patch test. Allergy. 2006;61:1377-84.
3. Spergel JM, Beausoleil JL, Mascarenhas M, Liacouras CA. The use of skin prick tests and patch tests to identify causative foods in eosinophilic esophagitis. J Allergy Clin Immunol. 2002;109:363- 8.
4. Spergel JM, Andrews T, Brown-Whitehorn TF, Beausoleil JL, Liacouras CA. Treatment of eosinophilic esophagitis with specific food elimination diet directed by a combination of skin prick and patch tests. Ann Allergy Asthma Immunol. 2005;95:336-43.
5. Spergel JM, Brown-Whitehorn T, Beausoleil JL, Shuker M, Liacouras CA. Predictive values for skin prick test and atopy patch test for eosinophilic esophagitis. J Allergy Clin Immunol. 2007;119:509-11.
6. Fogg MI, Brown-Whitehorn TA, Pawlowski NA, Spergel JM. Atopy patch test for the diagnosis of food protein-induced enterocolitis syndrome. Pediatr Allergy Immunol. 2006;17:351-5.
Médico, Ambulatório de Alergia e Imunologia, Universidade Federal de Uberlândia (UFU), Uberlândia, MG, Brasil
We want to thank Dr. Silva Segundo for his interest in our recent paper and for the pertinent review on the utility of atopy patch tests (APT) for the diagnosis of IgE-mediated food allergies. Indeed, there is evidence that APT can be helpful in predicting outcomes of double-blind placebo-controlled food challenges. However, most of such studies have been carried out in children with atopic dermatitis or allergic gastroenteropathies such as food-sensitive eosinophilic esophagitis. The majority of patients seen by pediatric gastroenterologists have food-sensitive enteropathies that are not associated with atopic dermatitis or eosinophilic enteropathies.
Moreover, several limitations exist with APT, even in carefully selected patients, as reviewed recently by the European Academy of Allergy and Clinical Immunology.1 First and foremost are the limited and highly variable sensitivity and specificity of the APT. In the diagnosis of cow's milk allergy, the mean sensitivity (0.51) and specificity (0.86) of the APT are similar to those of skin prick tests. However, the sensitivity of the APT has been reported to vary enormously, from 0.18 to 0.89.1
Numerous factors may explain these limited results with APT. These include the potential lack of standardization of the test conditions: allergen source and concentration, vehicle employed, control material, duration of and material used for occlusion, and size of the chamber. Finally, even though the results of APT may correlate with the outcome of properly conducted food challenges, studies still need be carried out to show that the test results predict the outcome of food elimination diet on gastrointestinal symptoms.
1. Turjanmaa K, Darsow U, Niggemann B, Rance F, Vanto T, Werfel T. EAACI/GA2LEN position paper: present status of the atopy patch test. Allergy. 2006;61:1377-84.
Gastroenterologista e endoscopista pediátrica. Mestre, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre (FFFCMPA), Porto Alegre, RS, Brasil. Doutora, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brasil
Canada Research Chair, Immune-Mediated Gastrointestinal Disorders, Division of Gastroenterology, Montreal Children's Hospital, Montreal, Quebec, Canada. Professor, McGill University Health Center, Montreal, Quebec, Canada