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Lichenoid Reaction (Dermatomyositis)






Fig. 1:  In this lesion of dermatomyositis, the epidermis is thin and shows effacement of rete ridges. The upper portion of the dermis, particularly on the right, shows edema and lysis of fibrous tissue. Vessels are ectatic. At the tip of the green arrows and in their vicinity, there are lytic defects at the dermal-epidermal interface. In part, these appear to be dermolytic defects rather than lytic defects in the basal unit of the epidermis. The area at the tip of the red arrow will be emphasized in the following photomicrographs. Generally, the spaces among collagen bundles are widened. Inflammatory infiltrates are spotty and mild.


Fig. 2: The changes at the dermal-epidermal interface are those of a cell-poor lichenoid reaction. To dismiss such a pattern as an “interface reaction” begs the issue. There is histologic evidence that lymphocytes and histiocytes have mediated a lytic reaction at the dermal-epidermal interface and such changes are the essence of a lichenoid reaction. Centrally, the epidermal basement membrane is reduplicated and convoluted. There is dermal edema with lysis of collagen (blue arrow).  There are perivascular deposits of hyalin (red arrows). Spaces among the collagen bundles of the reticular dermis are widened and with a proper stain this alteration probably would qualify as a mucinosis. The reaction at the dermal-epidermal interface is cell poor. The keratin layer is little altered.


Fig. 3: The basal unit is atrophic and the cells of the superficial unit are hypertrophied and show the features of terminal differentiation. The basal layer is vacuolated and the basement membrane is duplicated in the patterns of convoluted lamellae
(blue arrows). A few lymphocytes and histiocytes are present in the small lytic defects in the basal layer. To the left of the red arrow there is a dilated vessel. Between this vessel and the red arrow there is a smudgy, eosinophilic deposit which has the qualities of fibrinoid. Edema and atrophy of collagen bundles are features of the reticular dermis.


Fig. 4: The pattern qualifies as a cell-poor lichenoid reaction of the type seen in the collagen-vascular diseases. Vacuolar changes are prominent at the dermal-epidermal interface and among the duplicated lamellae of the basement membrane. Histiocytes are entrapped among the lamellae of the basement membrane.


Fig. 5: The green arrows point to fragments of nuclear debris. The red arrows point to reduplicated basement membranes. Lytic defects in the basal layer at the tips of the blue arrows contain sparse infiltrates of lymphocytes and histiocytes. Coarsening of basement membrane is seldom as prominent in lesions of dermatomyositis as in lesions of LE.  On the left, a colloid body is present between a red arrow and a blue arrow.

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