Mycosis fungoides-like cells. Their presence in a case of pityriasic dermatitis with a comment on their significance as an indicator of primary T-cell dyscrasia.

A case of pityriasic dermatitis in which the histologic findings mimicked mycosis fungoides was examined ultrastructurally. Large numbers of mycosis-like cells were found in the dermis and within epidermal spongiotic vesicles. Such cells occur in the epidermal and dermal infiltrates of primary T-lymphocyte disorders, notably in mycosis fungoides, the Sézary syndrome, and parapsoriasis en plague. However, they have also been found in the dermal infiltrates of benign dermatoses, in some skin tumors, and occasionally in normal controls. They share ultrastructural features with transformed T lymphocytes. It is emphasized that cells with this morphology may be found in the skin in any condition involving T-cell transformation or dysplasia. The mere presence of cells with this morphology within skin infiltrates is insufficient evidence for the diagnosis of primary T-cell dyscrasia.