๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
PATHOLOGY
The histologic features of AD depend upon the clinical stage of the lesion sampled. Acute, exudative eczema is characterized by marked spongiosis, with intraepidermal fluid collection leading to the formation of vesicles (micro and macro) or even bullae. Some dermal edema may also be present, together with perivascular lymphocytes that extend into the epidermis and a variable number of eosinophils (Fig. 12.21A). In subacute lesions, vesiculation is absent whereas acanthosis, hyperkeratosis, and parakeratosis become evident (Fig. 12.21B). In chronic, lichenified AD, epidermal thickening is more pronounced in a pattern that may be either irregular or regular (psoriasiform). Changes in the granular layer vary from thickening secondary to rubbing, as seen in lichen simplex chronicus, to thinning when there is a psoriasiform pattern, seen in some nummular lesions. Spongiosis and inflammation are less conspicuous, but there may be an increased number of mast cells and dermal fibrosis.
These features are not specific, as similar findings are observed in other eczematous dermatoses such as allergic contact dermatitis. There are occasionally histologic clues to the etiology, such as individually necrotic keratinocytes that suggest an irritant contact dermatitis. However, a skin biopsy is usually more helpful in excluding other entities that can mimic AD clinically, such as mycosis fungoides.