Epidermolysis bullosa simplex (Koebner) is a keratin disorder. Ultrastructural and immunohistochemical study.

A skin biopsy specimen was obtained from a 1-month-old female with epidermolysis bullosa simplex (Koebner). Histologically, an intraepidermal separation was seen and considered to be formed by cytolysis of the epidermal basal cells. Ultrastructurally, the basal cells were lacking in cytoplasmic tonofilaments, and the initial change of the cytolysis seemed to be cleavages of the cytoplasm. Immunohistochemically, a basal cell keratin was expressed in a suprabasal cell layer but not in the basal cell layer, and a panepithelial keratin was not detected in the basal cell layer. These findings suggest that keratin production of the epidermal cells may be delayed, resulting in a weakness of the basal cells against minor trauma to the skin.