Diagnosis: Spongiotic Dermatitis
• Contact dermatitis, nummular dermatitis, photoallergic dermatitis, and atopic dermatitis all are “eczematous dermatoses,” the histologic hallmark of which is spongiosis (intercellular edema). The distinction is made clinically, not histologically.
• Acute spongiotic dermatitis shows a normal epidermis and may show marked intraepithelial vesiculation secondary to marked spongiosis. Subacute spongiotic dermatitis shows a moderately acanthotic epidermis with a parakeratotic stratum corneum and crust. Chronic dermatitis shows hyperkeratosis with parakeratosis, wedge-shaped hypergranulosis, and acanthosis. Spongiosis and inflammation are minimal, and papillary dermal fibrosis may be seen.
• Intraepidermal vesicles of acute spongiotic dermatitis may contain clusters of Langerhans cells in a flask shape.
• Nummular dermatitis is the prototypic example of subacute spongiotic dermatitis. Spongiosis is usually mild to moderate and lacks vesiculation.
• Eosinophils are not specific in spongiotic dermatitides but are usually more prominent in allergic contact dermatitis.
