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Diagnosing Epitheliotropic Lymphoma

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Epitheliotropic lymphoma, also known as cutaneous T-cell lymphoma (CTCL) is an uncommon skin cancer in dogs with typically poor prognosis. The overall median survival time for dogs has been reported at 264 days (cutaneous: 130 days; mucocutaneous/mucosal: 491 days). Because this disease typically causes erythema and pruritus, it may be misdiagnosed as allergic dermatitis until the disease is advanced. This practice pearls article will give you tips on when to add epitheliotropic lymphoma to your differential list and what tests to perform to get a diagnosis.

Recognizing Clinical Signs:

The classic lesion of CTCL is exfoliative erythroderma, in which the skin is erythematous, scaly, and pruritic. Sounds a lot like allergies, right? Anatomic distribution can be helpful in differentiating. Flea allergies typically cause lesions on the rump, inguinal skin and proximal medial thighs. Food and environmental allergies cause lesions on the paws, the face, the concave pinnae, and the ventral trunk. Diffuse erythema and scaling to the entire trunk should raise a red flag for CTCL.

Other clinical signs such as mucocutaneous involvement (depigmentation, erosions, ulcers) or nodules or plaques on the skin can help differentiate CTCL from allergic dermatitis.


The paw pads, typically unaffected in allergic dermatitis (which instead targets the interdigital skin), can be crusted, erosive, edematous or ulcerated.

Cytology Findings:

Because secondary bacterial infection is often common due to disruption of the normal skin barrier, cytology is helpful in identifying infection that should be addressed.

Large lymphocytes with multiple criteria of malignancy can occasionally be observed.


A diagnosis of CTCL is reached with confirmed histopathologic changes, such as infiltration of lymphocytes into the epidermis, the mucosal epithelium, and/or adnexa. Lymphocytes can either be diffusely infiltrated throughout the epidermis, or can aggregate into Pautrier’s microabcesses within the epidermis. Lymphocytes can vary in size depending on the stage of disease in the area being biopsied. When performing a biopsy, the skin should not be scrubbed prior to obtaining a sample. Immunohistochemistry can be used to identify specific T-cell and B-cell markers to plan treatment and should be discussed with a specialist if needed.


  1. Chan, CM et al. “Clinical Outcome and Prognosis of Dogs with Histopathological Features Consistent with Epitheliotropic Lymphoma: A Retrospective Study of 148 Cases (2003-2015).” VETERINARY DERMATOLOGY, vol. 29, no. 2, Apr. 2018, p. 154–+.
  2. Miller, WH et al. Muller and Kirk’s Small Animal Dermatology. Saunders, 2013.
  3. Rook, KA. “Canine and Feline Cutaneous Epitheliotropic Lymphoma and Cutaneous Lymphocytosis.” VETERINARY CLINICS OF NORTH AMERICA-SMALL ANIMAL PRACTICE, vol. 49, no. 1, Jan. 2019, p. 67–+.


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 About the Author: Brittany Lancellotti, DVM, DACVD

Dr. Brittany Lancellotti is a veterinary dermatologist at Veterinary Skin and Ear in Los Angeles, California and the founder and host of the Your Vet Wants You to Know podcast. While in veterinary technician school, she worked at the Animal Medical Center in New York City. She attended Western University of Health Sciences, graduating with honors and receiving numerous awards. After a rotating internship at Animal Specialty Group in Los Angeles, she completed a dermatology residency with Animal Dermatology Group in Pasadena. She is an international speaker and is passionate about educating, as well as minimizing fear, anxiety, and stress for pets, clients, and staff alike.


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