Quiz 18: What is your diagnosis?

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Diagnosis: Quiz 18

Quiz 18

Answer:  Allergic contact dermatitis

Criteria for diagnosis histopathologically: A hyperplastic epidermis covered by mounds of parakeratosis, some of them containing remnants of serum, in combination with a rather sparse superficial perivascular and interstitial infiltrate of lymphocytes and eosinophils are findings of longstanding allergic contact dermatitis. Thick-walled, dilated dermal vessels and extravasated erythrocytes are changes of stasis and hint to the location, namely, the leg.

Differential diagnosis histopathologically: Like pityriasis rosea and erythema annulare centrifugum, allergic contact dermatitis and nummular dermatitis cannot be differentiated on histopathologic grounds.

Criteria for diagnosis clinically: Plaques that are ill defined and have a dusky red color and are covered in part by scales are consonant with longstanding lesions of allergic contact dermatitis.

Differential diagnosis clinically: Longstanding stasis changes due to venous insufficiency, fungal infection, or psoriasis cannot be excluded on clinical grounds alone; therefore, biopsy is necessary to come to the accurate diagnosis.

Clinicopathologic correlation: The plaques result from the inflammatory cell infiltrate in the dermis and the epidermal hyperplasia. The scales are formed by parakeratosis. The dusky red hue is a consequence of dilated, erythrocyte-filled venules in the upper part of the dermis in combination with extravasated erythrocytes in the dermis.

Options for therapy predicated on knowledge of histopathologic findings: Identification and avoidance of the allergen and topical application of a corticosteroid are the measures that will lead to involution of the lesions over time.

1) Allergic contact dermatitis is the stereotype of spongiotic vesicular dermatitis. Early lesions are characterized by slight spongiosis that rapidly develops into intraepidermal vesicles, sometimes even into bullae.

2) The pace at which the process progresses depends on a variety of factors, such as the nature of the allergen, the duration of the exposure to the allergen, the anatomic site, and the immunologic characteristics of the host. In those instances when the process progresses more slowly, large blisters never occur.

3) Clinically, the term "acute" refers to the recent onset and often to the severity of the disease. Immunologically, allergic contact dermatitis represents a T cell-mediated delayed-type (type IV) hypersensitivity reaction.

4) In longstanding "chronic" lesions spongiosis is not observable any more; chronic allergic contact dermatitis basically is psoriasiform dermatitis.

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