๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
PATHOLOGY
Although the diagnosis of ACD is in large part a clinical one aided by the diagnostic procedure of patch testing, histology can sometimes be helpful. This is especially true when excluding other diagnoses, such as mycosis fungoides. The pathology of ACD is most helpful in acute
(ACD).A The allergen was neomycin from a topical antibiotic ointment. B The allergen was urushiol in poison ivy; this distribution pattern is seen in patients who wear gloves. A, Courtesy Jonathan Chan, MD.
A In this machine operator, the allergen was black rubber. B The allergen was methylisothiazolinone in sanitary wet wipes.
lesions, as subacute or chronic lesions often produce confusing patterns that are not diagnostic. Histologically, ACD is the prototype of spongiotic dermatitis. In the acute stage, there is a variable degree of spongiosis, with a mixed dermal inflammatory infiltrate containing lymphocytes, histiocytes, and a variable number of eosinophils. In moderate to severe reactions, marked spongiosis results in intraepidermal vesiculation (Fig. 14.11A). In subacute to chronic stages, epidermal hyperplasia, often psoriasiform, develops (Fig. 14.11B).
However, even when spongiotic dermatitis is present, clinicopathologic correlation is always required, as ACD is not the only cause of this reaction pattern. In addition, as with any dermatitis, the application of topical corticosteroids may alter the histologic findings. Occasionally, other histopathologic patterns are seen in ACD, as outlined in Table 14.1.
Fig. 14.5 Acute ยญvesiculobullous allergic contact dermatitis
Fig. 14.6 Acute allergic contact dermatitis with a prominent component of edema.A Periorbital edema, in addition to crusted and weeping plaques, due to poison ivy. B Allergic contact dermatitis to methylisothiazolinone in a wet wipe used to remove make-up. A, Courtesy Jean L. Bolognia, MD.
Fig. 14.7 Allergic contact dermatitis due to aloe-containing cream. The degree of involvement on the upper and lower lips is similar, as opposed to actinic cheilitis. In the latter scale is predominantly on the lower vermilion lip.
Fig. 14.8 Persistent hand dermatitis due to chronic allergic contact ยญdermatitis.
Fig. 14.9 Patterns of allergic contact dermatitis.A Due to nickel; lesions can also arise from metal braces and on the back at the site of bra clasps. B Due to rubber. C Due to dyes and resins in clothing. D Due to methylisothiazolinone. Some exposures can affect multiple sites and cause generalized dermatitis. CPAP, continuous positive airway pressure.
Table 14.1 Rare to uncommon presentations of allergic contact dermatitis