Download The classic presentation of ACD is a pruritic

The classic presentation of ACD is a pruritic, eczematous dermatitis
initially localized to the primary site of allergen exposure.
S Geometric, linear, or focal patterns of involvement are suggestive of
an exogenous etiology. For example, ACD from plants such as poison ivy,
poison oak, or poison sumac, typically presents as a linear or streaky
array of erythematous papules and vesicles. Occasionally, the sensitizing
substance in these plants, an oleoresin named urushiol may be aerosolized
when the plants are burned, leading to a more generalized and severe
eruption on exposed areas. Transfer of the resin from sources other than
directly from the plant (such as clothes, pets, or hands) may result in
rashes on unexpected sites (eg, genital involvement in a patient with
poison ivy). Because the mechanism of allergen exposure influences the
clinical presentation, relevant historic data gathered from thoughtful
questioning may prove as useful as the distribution of the lesions.
Importantly, ACD will vary morphologically depending on the stage of the
disease and severity of reaction. During the acute phase, lesions are
marked by edema, erythema, and vesicle formation. Stronger allergens
often result in vesicle formation, whereas weaker allergens often lead
to papular lesion morphology, with surrounding erythema and edema. In the
subacute phase, vesicular rupture leads to oozing, and scaly juicy papules
associated with weeping and crusting dominate the clinical picture.
Finally, the chronic phase is characterized by scaling, fissuring, and
lichenification. A key symptom for ACD is pruritus, which seems to occur
more typically than a symptom of a burning sensation. Moreover, there are
some noneczematous clinical variants of ACD (Table 24-1) that are
infrequently observed.18,19 Erythema multiforme-like ACD has been linked
primarily to exotic woods, topical medicaments, and numerous
miscellaneous chemicals. In contrast to true erythema multiforme, which
typically presents on acral sites, lesions of erythem.
multiforme-like ACD are typically at the periphery site of contact with
the allergen, fever is usually absent, and mucosal involvement is rare.
Purpuric ACD is mainly observed on the lower legs and/or feet and has been
reported with a wide variety of allergens, including rubber and textile
dyes. Lichenoid ACD is considered a rare variant that can mimic lichen
planus; it is associated with color developers and metallic dyes in
tattoos. Also, oral lichenoid ACD from dental amalgams can resemble
typical oral lichen planus. Pigmented ACD has been mainly described in
Asian-ethnicity populations. It is linked to textile dyes, cosmetics, and
fragrances. Lymphomatoid ACD is based only on histopathologic criteria
(presence of significant dermal infiltrate displaying features of
pseudolymphoma). Nonspecific clinical signs include erythematous plaques,
sometimes very infiltrated, at the site of application of the contact
allergen. Allergens implicated in lymphomatoid ACD include metals (nickel
and gold), para-phenylenediamine (hair dye), para-tert-butylphenol resin
(glue), and dimethylfumarate (a mold inhibitor found in sachets within
some furniture implicated in causing a previously severe epidemic of ACD).