Cutaneous epitheliotropic lymphoma (CETL) in dogs is rare.There are 3 subforms based on criteria in humans:mycosis fungoides (MF), pategoid reticulosis (PR), and Sézary syndrome (SS).MF involves the entire body, PR is a localized“benign” form, and SS is associated with neoplastic lymphocytes in the lymph nodes and blood.The cause in dogs is unknown, and many studies have looked at whether chronic inflammation and chronic activation of T-cells is a predisposing factor. Some findings suggest that dogs with atopy may be at higher risk, but further studies are needed to assess the relationship between chronic allergic skin disease and neoplasia. In veterinary medicine, there are very few well-documented and confirmed cases of PR or SS, and classification based on clinical presentation is more useful. Early cases of CETL often present with diffuse erythema and scaling (exfoliative erythroderma).This form typically progresses to the“patch, plaque, and nodule” form. Patches and plaques present together,with nodules following soon after.A common form in dogs is the mucocutaneous form, characterized by erythema, infiltration, erosions, and ulcerations at the mucocutaneous junctions. It mostly affects the lips, nose, and eyelids. In some dogs, lesions are limited to the oral mucosa.Diagnosis is made by biopsy of affected tissues.Neoplastic T-cells can be differentiated by cluster of differentiation antigens. In classic CETL, neoplastic cells are positive for CD3+ markers. In 80% of cases, CD4–/CD8+ cytotoxic T-cells are found. In 20% of cases, CD4–/CD8– lymphocytes (natural killer cells) are found.Other protein markers that can be used include T-cell receptor and Ki-67. Finally, clonal proliferation occurs from a single lymphocyte; the population of neoplastic cells contains the same signature gene rearrangement. In contrast, reactive lymphocytes contain a mixture of gene rearrangements that is useful in differentiating CETL in borderline cases.The prognosis for dogs with cutaneous CETL is poor, and many clients elect euthanasia.One of the most promising treatment protocols includes the use of lomustine or CCNU (cyclonexyl-chloroethyl-nitrosourea).

COMMENTARY: In many cases, the clinical presentation of dogs with cutaneous epitheliotropic lymphoma strongly suggests the disease.Dogs in which this condition should be suspected include middle-age dogs with no history of skin disease that suddenly develop exfoliative erythroderma or nonresponding seborrhea, dogs with intense pruritus that cannot otherwise be explained, dogs with multifocal areas of raised indurated plaques, and, of course, dogs with tumors. In my experience, the mucocutaneous form is most commonly found in dogs that suddenly develop lipfold pyoderma.Oral disease can be associated with inappetence, excessive salivation, changes in behavior, or halitosis.This disease highlights the need to biopsy skin lesions that are unusual in appearance or when skin diseases do not respond as expected.—Karen A. Moriello, DVM, Diplomate ACVD

Canine cutaneous epitheliotropic T-cell lymphoma:A review. Fontaine J, Bovens C, Bettenay S,Mueller RS.VET COMP ONCOL 7:15-27, 2009.