Atopic Dermatitis, food allergy and dietary interventions. A tale of controversy

Abstract

Atopic Dermatitis has long been a controversial entity in regard its relationship to food allergy. Indeed, inter-discipline disparity in the way dermatologists and allergologists perceive the food allergy/atopic dermatitis interplay, hampers the design of concise therapeutic strategies and conveys conflicting messages to the patients. Within this conceptual frame, food exclusion regimes are rendered a contentious option. On the basis of this acknowledgment, we opted to put the emphasis on the discrepant perceptions surrounding such therapeutic regimes and to share our view pertaining to their appropriate implementation.

INTRODUCTION

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by pruritic eczematous lesions. AD is elicited by various stimuli including inhaled/food allergens, irritating substances and infectious microorganisms.¹ Among food allergens, cow's milk, hens' eggs, wheat, soy, tree nuts and peanuts are the most commonly reported culprits.² Nevertheless, a causal relationship between food allergy and AD is controversial.¹ Indeed, a dichotomy exists as to whether the increased prevalence of food allergy in AD patients is a parallel occurrence rather than an AD contributing factor.^1,3 Furthermore, even though food allergy is increasingly implicated in certain forms of AD, food exclusion is not a familiar concept in the dermatological setting and it is generally frowned upon.^4,5

Impelled by this intra-field inconsistency we opted to assess the exposure of dermatologists and allergologists to pertinent information. To this end, we performed a Pubmed search using combination of the key words: "Atopic dermatitis", "eczema" and "food allergy" in six reputable scientific journals of dermatological orientation (Journal of the European Academy of Dermatology and Venereology, Journal of the American Academy of Dermatology, British Journal of Dermatology, Journal of Investigational Dermatology, Clinical and Experimental Dermatology, Experimental Dermatology) and six of allergologic interest (Journal of Allergy and Clinical Immunology; Clinical and Experimental Allergy; Allergy; Annals of Allergy, asthma and immunology; International Archives of Allergy and Immunology; Clinical and Molecular Allergy). Our search in the dermatological journals returned 40 reports; 17 were irrelevant and 11 were case reports/short communications/letters to the editor. The articles collectively conveyed a rather negative message towards food exclusion diets. In sharp contrast, our search in the allergologic literature yielded 378 reports with the vast majority of them assuming a positive stance towards food interventions. From this perspective, although allergy-oriented journals publish numerous food allergy related reports ex vi termini, it strikes us as odd that the specialists primarily treating AD patients, i.e. dermatologists, are exposed to considerably limited relevant information.

Therefore our aim is to emphasize such controversial cross-discipline perceptions and to convey our views pertaining to the appropriate implementation of food exclusion regimes.

DISCUSSION

The pathophysiology of AD remains unclear.¹ As there is no definite cure, patients often undertake avoidance of fish, seafood, beef, eggs and dairy products without medical supervision, hence triggering malnutrition-related pathology.⁶ Furthermore, various allergy tests are readily available in pharmacies and laboratories, where they are performed outside their medical context. Therefore, a false interpretation may erroneously drive a patient into obstinate avoidance of certain foodstuffs, a decision further instigated by conflicting cross-discipline medical guidance.⁴ A recent Cochrane review questioning the efficacy of food exclusion diets - except for eggs - in unselected populations, further perplexes their evaluation.⁷ Nevertheless, it does not conclusively refute dietary interventions in selected patients. Indeed, the ADaggravating capacity of food intake in certain clusters of patients, has been well documented.⁸

In regard to when such measures should be implemented, reports of consistent correlation of food intake with AD exacerbations are invaluable. Suspicion of a certain food should lead to skin-prick tests (SPTs) and serum specific IgE determination (RAST) to assess type I reactions or atopy patch tests (ATP) for type IV reactions - albeit usefulness of the later is controversial.⁹ If both history and diagnostic tests furnish information suggestive of food allergy involvement, dietary intervention could be undertaken. However, in vivo or in vitro identification of IgE sensitization to a certain food should not include barring it from the patients diet in the absence of indications of clinical relevance. Furthermore, disease abatement during an elimination diet could be coincidental, as AD runs a course of relapses and remissions. On the basis of this acknowledgment, symptoms should be reproduced following an oral food challenge (OFC). Double-blind-placebo-controlled OFCs comprise the cornerstone of diagnosis but their considerable cost and labor-heavy nature impede their routine use in favor of open-label or single-blind OFCs. If the medical history is inconclusive albeit nonspecific suspicion arises, an oligoantigenic diet, i.e. administration of low-danger foodstuffs, can be implemented. Duration of the diet should be limited and -if remission ensues- foods should be reintroduced gradually in order for an AD trigger to be identified

A link between food allergy and AD, albeit possible in infants, is questionable in adults.¹⁰ Furthermore, in adults, ingestion of histamine-releasing foods can confound accurate diagnosis of true food allergy. Nevertheless, AD aggravation by pollenassociated cross allergens and by non-typical mechanisms (f.e. food additives) should not be readily dismissed in this age group.

CONCLUDING REMARKS

Most of the AD cases under self-imposed dietary manipulations most likely face malnutrition issues and uncontrolled disease due to poor skin care. This situation has the potential to bias dermatologists into readily dismissing well-designed food exclusion regimes. Within this conceptual frame we emphasize the need for food allergy testing and potential dietary interventions in refractory AD cases, where an topic predisposition is highly suspected. In a broader context, we prompt for allergological consultancy of such patients upon failure of conventional skin treatment.