Investigations
1st investigations to order
clinical diagnosis
Test
Usually no tests are necessary.
Result
features of eczema; xerosis, hyperlinear palms, inflammatory papules, lichenification
Investigations to consider
IgE levels
Test
Not routinely performed if diagnosis is clear on grounds of history and examination.[63]
Testing for food allergy in patients with eczema should not be considered before intervention with patient education and optimal skin care, including topical corticosteroids, has been initiated.[52]
In the UK, a diagnosis of food allergy should be considered in children with eczema who have reacted to a food with immediate symptoms, or in infants and young children with moderate or severe eczema that is not controlled by optimal management, particularly if associated with gut dysmotility, or with failure to thrive.[46]
High sensitivity and low specificity of skin-prick and IgE testing for food allergy can yield false positive results, which may lead to elimination diets that are potentially harmful to patients with eczema.[52] Effects such as progression to immediate-type allergy, including anaphylactic reactions, have been reported.[52][53][54][55]
Therefore, skin-prick or IgE testing should only be considered for patients who have a history of allergy to food (e.g., exacerbation of eczema after consumption of egg).[52][55][56]
Special consideration should be given to infants with severe eczema, egg allergy, or both, as they have the highest a priori risk for developing peanut allergy.[57] An IgE or skin-prick test is strongly recommended before introducing peanuts into their diet.[52]
Result
elevated IgE blood levels
skin-prick testing
Test
Not routinely performed if diagnosis is clear on grounds of history and examination.[63]
Testing for food allergy in patients with eczema should not be considered before intervention with patient education and optimal skin care, including topical corticosteroids, has been initiated.[52]
In the UK, a diagnosis of food allergy should be considered in children with eczema who have reacted to a food with immediate symptoms, or in infants and young children with moderate or severe eczema that is not controlled by optimal management, particularly if associated with gut dysmotility, or with failure to thrive.[46]
High sensitivity and low specificity of skin-prick and IgE testing for food allergy can yield false positive results, which may lead to elimination diets that are potentially harmful to patients with eczema.[52] Effects such as progression to immediate-type allergy, including anaphylactic reactions, have been reported.[52][53][54][55]
Therefore, skin-prick or IgE testing should only be considered for patients who have a history of allergy to food (e.g., exacerbation of eczema after consumption of egg).[52][55][56]
Special consideration should be given to infants with severe eczema, egg allergy, or both, as they have the highest a priori risk for developing peanut allergy.[57] An IgE or skin-prick test is strongly recommended before introducing peanuts into their diet.[52]
Reactions are assessed by the degree of redness and swelling and the size of the weal produced.
Result
reactivity to allergen
oral food challenge
Test
Testing for food allergy in patients with eczema should not be considered before intervention with patient education and optimal skin care, including topical corticosteroids, has been initiated.[52] Patients under 5 years old with moderate to severe eczema, who are unresponsive to initial treatment, should be tested for food allergy using oral food challenge or trial elimination diet.[52]
In the UK, a diagnosis of food allergy should be considered in children with eczema who have reacted to a food with immediate symptoms, or in infants and young children with moderate or severe eczema that is not controlled by optimal management, particularly if associated with gut dysmotility, or with failure to thrive.[46]
Result
exacerbation of eczema symptoms after oral food challenge
trial elimination diet
Test
Testing for food allergy in patients with eczema should not be considered before intervention with patient education and optimal skin care, including topical corticosteroids, has been initiated.[52] Patients under 5 years old with moderate to severe eczema, who are unresponsive to initial treatment, should be tested for food allergy using oral food challenge or trial elimination diet.[52]
In the UK, a diagnosis of food allergy should be considered in children with eczema who have reacted to a food with immediate symptoms, or in infants and young children with moderate or severe eczema that is not controlled by optimal management, particularly if associated with gut dysmotility, or with failure to thrive.[46]
Result
improvement in eczema symptoms after trial elimination diet
patch testing
Test
Allergic contact dermatitis may complicate the clinical course of eczema. Patch testing should be considered for any child or adult whose dermatitis remains difficult to control or presents in a specific location suggestive of an external trigger.[58][59][60]
Diagnosis is by patch testing, whereby suspected allergens are placed on unaffected skin of the back for a period of 48 hours. Irritant reactions are evaluated when the patch is removed, and again at subsequent follow-up appointments for delayed reactions.
Common contact allergens in patients with eczema include, but are not limited to, nickel, neomycin, fragrance, formaldehyde, and rubber chemicals.[56]
Result
reactivity to allergen
skin biopsy
Test
May be considered to differentiate eczema from allergic contact dermatitis, and also from mycosis fungoides or psoriasis.[63][65]
Used less frequently than skin examination, which considers primary lesions, their distribution, the associated symptomatology, and the skin disease's duration and associations at the time of onset.
Result
findings consistent with eczema including spongiosis acanthosis, and chronic inflammatory infiltrate, mainly composed of lymphocytes, mast cells, and eosinophils
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