Canine Epidermotropic Lymphoproliferative Disease Resembling Pagetoid Reticulosis in Man

Gross lesions in a dog with cutaneous lymphoproliferative disease involved oral mucosa, and footpad and nasal epithelia. The lesions were vesicles, ulcers, erythematous papules, and plaques. The distinctive histologic feature was the predominantly intraepithelial proliferation of a monomorphous population of atypical mononuclear cells, many with bizarre convoluted nuclei. Ultrastructurally the mononuclear cells had few cytoplasmic organelles and resembled lymphocytes. These features distinguish the lesion from the usual canine cutaneous lymphosarcoma and from the canine equivalent of mycosis fungoides. The histology resembles that of pagetoid reticulosis in man.