15 Epitheliotropic lymphoma
Cutaneous lymphoma is subdivided histologically into epitheliotropic and non-epitheliotropic forms. Cutaneous epitheliotropic lymphoma is an uncommon condition, characterized by infiltration of neoplastic T lymphocytes into the epidermis and the follicular epithelium. The condition mainly occurs in dogs, but it has also been reported in cats, ferrets, hamsters, rats and mice. In humans, epitheliotropic lymphoma is commonly referred to as mycosis fungoides and this term is often loosely used for the disease in animals. An advanced form of mycosis fungoides in man, the ‘Sezary syndrome’, is characterized by generalized, exfoliating erythroderma, pruritus, peripheral lymphadenopathy and large number of circulating malignant lymphocytes. The d’emblée form of epitheliotropic lymphoma in man refers to a rapidly progressive form of the disease. A subclassification of mycosis fungoides is Pagetoid reticulosis, where histologically there is striking epidermotropism. In dogs these terms are not always useful, as the clinical signs and the progression of the disease vary from that in humans, but are nevertheless used in histological classification. Canine epithelioptropic lymphoma is progressive and often poorly responsive to treatment.
A common observation in cases of canine epitheliotropic lymphoma is failure to respond to any particular treatment and an associated progression of symptoms, but the deterioration rate varies between individuals. Some dogs may be pruritic. Most do not exhibit signs of systemic disease unless there is internal metastasis but lethargy may be reported. Some dogs may have a history of allergic skin disease that had previously been relatively well managed.