Spongiotic dermatitis refers to a group of disorders in which inflammation is focused on the epidermis and papillary dermis. Its hallmark is intercellular edema of the epidermis. This is associated with exocytosis of lymphocytes and a papillary dermal perivascular infiltrates of lymphocytes with or without eosinophils. In the acute phase, the spongiosis may be so severe that it can result in intraepidermal vesicles. In the subacute phase, the spongiosis decreases and the epidermis becomes hyperplastic, resulting in acanthosis and often parakeratosis. In the chronic phase, especially in the face of repeated scratching and or rubbing, epidermal hyperplasia progresses and the papillary dermis becomes thickened, resulting in lichenification.

Spongiotic dermatitis may be allergic contact, atopic, nummular, stasis, photoinduced, and more. Certain histological clues may favor some forms of dermatitis over others. For example, the presence of so-called acute on chronic spongiotic dermatitis (referring to the combination of both epidermal hyperplasia and acute spongiosis) is characteristic of nummular dermatitis and chronic allergic contact dermatitis. Lichenification is more likely to be seen in patients with atopic dermatitis. The presence of prominent stasis changes in the papillary dermis underlying spongiotic epidermis raises strong suspicion for stasis dermatitis.

In general, a practitioner would not expect the pathologist to “type” the dermatitis but instead confirm the diagnosis to the exclusion of other disorders. On the other hand, an overzealous pathologist may attempt to make a specific diagnosis when the findings are simply those of spongiotic dermatitis. It is the practitioner’s duty to diagnose the type of dermatitis of the patient based on the history and physical examination.