The varieties of “eczema”: clinicopathologic correlation

Eczema is defined in the third Webster’s unabridged dictionary as an “acute or chronic noncontagious inflammatory condition of the skin characterized by redness, itching, oozing...associated with exposure to chemicals or irritants.” The word derives from Greek, meaning literally to erupt, ferment, or boil. The broadness of this term and its association with just about any inflammatory condition of the skin has prompted some authors to opine that “ it is devoid of meaning” and that it should be “expunged” from the dermatologic lexicon. The consensus among many dermatopathologists and a few dermatologists is that the expression eczema should be replaced with the term “spongiotic dermatitis.” Spongiosis refers to the histopathologic changes that underlie most of the so-called eczemas, ie, edema between the keratinocytes of the stratum malpighii, which gives a spongy appearance to the epidermis. Although most authors have accepted this concept, it is actually a gross oversimplification. Spongiosis occurs in numerous other dermatoses that are not, by conventional wisdom, classified as “eczema.” Examples include, but are not limited to pityriasis rosea, Gianotti Crosti syndrome, the annular erythemas, miliaria, Grover’s disease, polymorphous light eruptions, papular urticaria, lichen striatus, and some pigmented purpuras. Because a full discussion of this issue is beyond the scope of this article, for purposes of discussion, eczema is defined here as “an inflammatory skin disorder that histologically shows spongiosis and is related etiologically to some type of immunologic perturbation.” This review will cover two major points concerning spongiotic dermatitis. First, spongiotic dermatitis will be examined as a histologic continuum. If the antigenic insult is severe and reaction time is short, the resulting dermatitis is designated as acute. If the antigenic stimulus is weaker and takes place over an extended period of time, then it is referred to as chronic. Severe chronic reactions typified by maximal physical changes are termed lichen simplex chronicus and prurigo nodularis. Although this histopathologic schema is a convention in common use by dermatopathologists, it should be understood that pathologic changes don’t always correlate exactly with a defined time course in a clinical dermatitis. The second major consideration of this paper will be the varieties of spongiotic dermatitis that occur at different anatomic sites and that may have varying etiologies. An attempt will be made to differentiate the characteristic histopathologic changes occurring at different anatomic locations and those occurring within different subtypes of spongiotic dermatitis; we will also discuss whether such changes can be readily identified by the dermatopathologist. For some of the dermatitides, a short summary of pathogenesis is included if it is relevant to understanding the pathology. There are five general categories of spongiotic dermatitis: 1) acute spongiotic dermatitis; 2) subacutespongiotic dermatitis; 3) chronic spongiotic dermatitis; 4) lichen simplex chronicus; and 5) prurigo nodularis. The first three categories actually represent a pathologic continuum, whereas the last two are a pathologic response to trauma superimposed by the patient on the underlying dermatitis. In acute spongiotic dermatitis, the spongiosis is typified by massive intercellular edema of the epidermis with widening of the intercellular spaces. The edema produces disruption of desmosomal attachments, and as a consequence, numerous microvesicles form. Although these vesicles are usually intraepidermal, with sufficient vesiculation they can become subepidermal. In general, the degree of epidermal acanthosis is slight. Dermal edema is common, and it is often accompanied by a pronounced inflammatory infiltrate of mononuclear cells and eosinophils. Although there may be some parakeratosis, in general, the changes in the horn are slight given the rapidity at which the process usually develops. A frequent accompaniment is a scale crust composed of neutrophils, plasma, and bacterial colonies ie, so-called impetiginization (Fig. 1). In subacute spongiotic dermatitis, the vesicles are smaller and there is greater acanthosis of the epidermis. From the Departments of Dermatology and Pathology, Mount Sinai School of Medicine, New York, New York. Address correspondence to Dr. Robert G. Phelps, Dermatopathology Division, Box 1194, 1 Gustave L. Levy Place, New York, NY 10029. E-mail address: bobpderm@aol.com.