Biopsy of Skin of Forehead
The epidermis shows occasional vacuolated basal cells. In addition, there are scattered lymphocytes in the underlying dermis and clusters of lymphocytes around the superficial vessels (center). A mild edema and an increase in faintly bluish matrix are also present. This inflammatory reaction produces the hyperemia that accounts for the rash.
The diagnosis is atrophic vacuolar interface dermatitis. This pattern is characteristic of dermatomyositis, but can also be seen in lupus erythematosus.
Comment: The term atrophic refers to a thinning of the epidermis with loss of rete ridges. The term "vacuolar interface" refers to the clear spaces around the nuclei in the basal layer of the epidermis or interface between the dermis and epidermis. The vacuolar change is thought to represent a cytotoxic immune reaction.
In a study of the immunopathologic changes in dermatomyositis, it was found that most of the cells in the dermis and perivascular infiltrates were T lymphocytes, and that CD4 T cells tended to predominate over CD8 T cells. Differences in cell types could not be detected between treated and untreated patients or at different stages of the disease, but involved skin had more infiltrates than uninvolved skin. Small numbers of macrophages and a few Langerhans' cells were mixed with the lymphocytes. B lymphocytes were not found. The presence of Langerhans' cells in the infiltrates suggests that local activation of T lymphocytes is occurring. The immunophenotype described here is similar to that reported in lupus erythematosus .
Subcutaneous calcifications may be a feature of dermatomyositis, especially in children. They may erode to the surface or involve deeper tissues .
1. Hausmann G, Herrero C, Cid M, Casademont J, Lecha M, Mascaró J. Immunopathologic study of skin lesions in dermatomyositis. J Am Acad Dermatol 1991; 25:225-230.ok
2. Dalakas M. Calcifications in dermatomyositis. N Engl J Med 1995; 333:978.