Mycosis Fungoides Manifesting as Giant Cell Lichenoid Dermatitis.

Mycosis fungoides (MF) is the most common form of primary cutaneous lymphoma with a broad clinicopathological spectrum. Unusual histopathologic patterns of MF include lichenoid, interstitial, folliculotropic, spongiotic, granulomatous, and many others. Several cases of unusual lichenoid reaction characterized by a mixed lichenoid inflammatory infiltrate with prominent infiltration of the papillary dermis and epidermis by multinucleated giant cells were described under the name of "giant cell lichenoid dermatitis," most of them were considered to represent a drug eruption. Herein, we describe a 77-year-old woman with a 5-year history of MF displaying microscopic features of giant cell lichenoid dermatitis. Histology revealed a dense band-like lichenoid epidermotropic infiltrate composed of CD4 small to medium-sized lymphocytes with cerebriform nuclei with the presence of multinucleated giant cells in the papillary dermis, within the epidermis, and some hair follicles. Monoclonal TCR gene rearrangement was detected using PCR. To the best of our knowledge, this pattern was never described in MF.