EPITHELIOTROPIC CUTANEOUS LYMPHOMA IN 3 D OGS - DIFFERENTIAL DIAGNOSTIC IDENTIFICATION BY IMMUNOHISTOCHEMICAL DEMONSTRATION OF T-CELL-SPECIFICITY OF THE CUTANEOUS INFILTRATE

Epitheliotropic cutaneous lymphoma (Mycosis fungoides) has been report ed in the dog, cat, calf and syrian hamster according to similarities to the human entity. Besides some clinical and histological difference s of this disease in dogs and humans, it has been recently demonstrate d that in dogs it is based an a degeneration of CD8-positive T-lymphoc ytes, whereas in humans a CD4 origin of the cutaneous infiltrate has b een described in most cases. Moreover, some clinical and histological lesions in the dog give rise to diagnostic confusion with other epider motropic neoplasms and autoimmune skin diseases. Epithelial Pautrier-m icroabscesses and Sezary- or Lutzner-cells which are regarded as chara cteristic for epitheliotropic cutaneous lymphoma cannot be found in al l cases for proof of the diagnosis. However, the differential diagnost ic separation from other diseases is important with regard to clinical prognosis and therapy. In this study, three clinically different case s of epitheliotropic cutaneous lymphoma in the dog are described with special focus on the methods for confirmation of the diagnosis, especi ally immunohistochemical examination of suitable skin biopsies. In two of these three cases, the diagnosis was possible due to histological changes in the skin, whereas in the third case a histology-based suspi cion was confirmed by immunohistochemical characterization of the cuta neous infiltrate. In all three cases, CD8-reactivity of the majority o f the infiltrating cells was demonstrated. In conclusion, immunohistoc hemical phenotypization is an important diagnostic tool for identifyin g epitheliotropic cutaneous lymphoma in the dog in those cases where c haracteristic changes are missing or disguised by secondary lesions.