Sézary syndrome arising from cutaneous epitheliotropic T-cell lymphoma, resembling human folliculotropic mycosis fungoides, in a dog.

A 9-year-old neutered male Pug dog presented with a history of chronic dermatitis. Dermatological examination revealed skin thickening with keratin fronds, erythematous macules and generalized lymphadenopathy. Haematology revealed leucocytosis with lymphocytosis and medium to large neoplastic lymphocytes having cerebriform nuclei (Sézary cells). Fine-needle aspirate samples from the skin and the superficial lymph nodes contained pleomorphic medium-sized lymphocytes and a cytological diagnosis of lymphoma was made. The dog was euthanized. In addition to the cutaneous lesions, post-mortem examination revealed lymphadenomegaly, splenomegaly and hepatomegaly. Histological examination of the skin revealed a neoplastic proliferation of large lymphocytes infiltrating the deep dermis and surrounding the hair follicles. Similar neoplastic cells were present in the lymph nodes, spleen, liver and bone marrow. Neoplastic cells were immunoreactive for CD3 and not for PAX-5. The final diagnosis was Sézary syndrome arising from cutaneous epitheliotropic T-cell lymphoma resembling human folliculotropic mycosis fungoides.