These are links to a videoclip (prepared by Dr. John R. Minarcik, human pathologist from IL, USA) of a histopathology case of mycosis fungoides (MF, epitheliotropic T-cell lymphoma, epidermotropic cutaneous lymphoma) in a person: http://www.youtube.com/watch?v=roRa2-NWN3g&feature=relmfu, and to microscopic pictures of a case of the same disease in a dog http://www.cytopath.co.uk/caseofmonthaugust2010.html (Case of The Month section from the Cytopath Veterinary Diagnostic Laboratory in Herefordshire, UK) and in a horse http://vp4.afip.org/wsc/wsc95/images/c28c4b.jpg and http://vp4.afip.org/wsc/wsc95/images/c28c4a.jpg (AFIP Dept Vet Pathol DODVPR WSC).


Cutaneous epitheliotropic T-cell lymphoma is a neoplastic disease of the skin of humans, dogs, cats, SD rats, Syrian hamsters, pigtailed macaques, squirrels, and coatis. It is characterized by the infiltration of the epidermis and adnexal structures of the skin by neoplastic lymphocytes (neoplastic T cells). Clinically, epitheliotropic cutaneous T-cell lymphoma in dogs can occur throughout the skin, and can also have a marked tendency to involve mucocutaneous junctions (lips, nasal planum, eyelids, perianal junction, perivulvar junction) and oral cavity (buccal mucosa, gingiva, palate, tongue). Footpads and interdigital folds can be involved too. The broad spectrum of clinical signs in early-stage cutaneous epitheliotropic T-cell lymphoma is a diagnostic challenge. The disease in dogs closely resembles human mycosis fungoides in that most cases are initially presented with lesions that clinically and histologically resemble many inflammatory skin diseases (including lupus erythematosus and pemphigus), and often progresses rapidly and unrelentingly to a more aggressive, severe tumor stage. Early diagnosis of canine epitheliotropic cutaneous T-cell lymphoma by histopathology/immunohistochemistry/PCR is essential in order to start soon with a specific oncologic therapy.


Monoclonal antibodies specific for canine lymphocyte antigens used for the immunohistochemical phenotyping of T lymphocytes from cutaneous epitheliotropic T-cell lymphoma in dogs include: CD3-specific mAb, CD4, CD8 alpha, CD8 beta, CD21, CD45RA, TCR beta subunit, and TCR gamma delta.


The immunophenotypic features of epitheliotropic lymphomas of the skin of humans are: most cases are CD4+ (CD4 positive helper T cell) and TCRab+ (T cell receptor alpha beta positive), and few cases are CD8+ (CD8 positive cytotoxic T cell) and TCRgd+ (T cell receptor gamma delta positive).


The immunophenotypic features of epitheliotropic lymphomas of the skin of dogs are: most cases are CD8+, and few cases are double negative CD4- and CD8-.


The immunophenotypic features of epitheliotropic lymphomas of the skin of cats are: CD3+ and double negative (CD4-, CD8-). An article about feline cutaneous epitheliotropic lymphomas was just published on Vet Dermatol (Early View, 05.02.2011) – read the abstract of this paper here:  http://www.ncbi.nlm.nih.gov/pubmed/21535252


The key histopathological diagnostic feature of epitheliotropic T-cell lymphoma is the tropism of the neoplastic lymphoid T cells for the epidermal or mucosal epithelium and the adnexal structures of the skin, in particular the wall of the hair follicles. The intraepithelial neoplastic lymphocytes are either diffusely distributed within the epithelium or form discrete aggregates (nests) referred to as “Pautrier’s microaggregates”, “Pautrier’s microabscesses” or “Pautrier collections”. Diffuse infiltrates of neoplastic T cells tend to remain in the lower levels of the epidermis. Tropism to the cutaneous adnexa may be more prominent than invasion into the epidermis, and complete obliteration of the hair follicles and adnexal glands of the skin may occur. Infiltration of apocrine sweat glands may be striking in some cases, and is highly diagnostic for epitheliotropic T-cell lymphoma since inflammatory infiltrates generally do not occur in such location.


Suggested readings: I recommend that you read more about mycosis fungoides in the following books and papers:


Books:


Gross TL et al. 2007. Skin diseases of the dog and cat: clinical and histopathologic diagnosis http://books.google.com/books?id=VKa2Wo3Wc-kC&printsec=frontcover&source=gbs_navlinks_s#v=onepage&q&f=false


Elder DE et al. 2007. Atlas and synopsis of Lever’s histopathology of the skin http://books.google.com/books?id=-uqJzY08OqUC&printsec=frontcover#v=onepage&q&f=false


Articles:


Doe R et al. Canine epidermotropic cutaneous lymphoma. Am J Dermatopathol. 1988 Feb;10(1):80-86. http://www.ncbi.nlm.nih.gov/pubmed/3177825


Moore PF et al. Canine cutaneous epitheliotropic lymphoma (mycosis fungoides) is a proliferative disorder of CD8+ T cells. Am J Pathol. 1994 Feb;144(2):421-429. http://www.ncbi.nlm.nih.gov/pubmed/7906096


Olivry T et al. Investigation of epidermotropism in canine mycosis fungoides: expression of intercellular adhesion molecule-1 (ICAM-1) and beta-2 integrins. Arch Dermatol Res. 1995;287(2):186-192. http://www.ncbi.nlm.nih.gov/pubmed/7539248


Magnol JP et al. Clinical, morphologic and immunophenotypic data based on 10 cases of canine muco-cutaneous epidermotropic T-lymphoma (analogous to Mycosis Funcgoïde). Important of an animal model of spontaneous pathology. Bull Acad Natl Med. 1996 Feb;180(2):449-462. http://www.ncbi.nlm.nih.gov/pubmed/8705383


Wilcock BP & Yager JA. The behavior of epidermotropic lymphoma in twenty-five dogs. Can Vet J. 1989 Sep;30(9):754-756. http://www.ncbi.nlm.nih.gov/pubmed/17423425


McKeever PJ et al. Canine cutaneous lymphoma. J Am Vet Med Assoc. 1982 Mar 1;180(5):531-536. http://www.ncbi.nlm.nih.gov/pubmed/7061338


Day MJ. Immunophenotypic characterization of cutaneous lymphoid neoplasia in the dog and cat. J Comp Pathol. 1995 Jan;112(1):79-96. http://www.ncbi.nlm.nih.gov/pubmed/7722010


Czasch S et al. Central nervous system metastasis of a cutaneous epitheliotropic lymphosarcoma in a dog. J Comp Pathol. 2000 Jul;123(1):59-63. http://www.ncbi.nlm.nih.gov/pubmed/10906257


Fivenson DP et al. T-cell receptor gene rearrangement in canine mycosis fungoides: further support for a canine model of cutaneous T-cell lymphoma. J Invest Dermatol. 1994 Feb;102(2):227-30. http://www.ncbi.nlm.nih.gov/pubmed/7906287


Donaldson D & Day MJ. Epitheliotropic lymphoma (mycosis fungoides) presenting as blepharoconjunctivitis in an Irish setter. J Small Anim Pract. 2000 Jul;41(7):317-20. http://www.ncbi.nlm.nih.gov/pubmed/10976628


Ferrer L et al. Immunohistochemical detection of CD3 antigen (pan T marker) in canine lymphomas.  J Vet Diagn Invest. 1993 Oct;5(4):616-620. http://www.ncbi.nlm.nih.gov/pubmed/8286465


Neta M, Naigamwalla D, Bienzle D. Perforin expression in feline epitheliotropic cutaneous lymphoma.  J Vet Diagn Invest. 2008 Nov;20(6):831-5. http://www.ncbi.nlm.nih.gov/pubmed/18987241


Chaubert P et al. Improved polymerase chain reaction-based method to detect early-stage epitheliotropic T-cell lymphoma (mycosis fungoides) in formalin-fixed, paraffin-embedded skin biopsy specimens of the dog. J Vet Diagn Invest. 2010 Jan;22(1):20-29. http://www.ncbi.nlm.nih.gov/pubmed/20093678


Foster AP et al. Cutaneous T-cell lymphoma with Sézary syndrome in a dog. Vet Clin Pathol. 1997;26(4):188-192. http://www.ncbi.nlm.nih.gov/pubmed/12658584


Fontaine J et al. Canine cutaneous epitheliotropic T-cell lymphoma: a review. Vet Comp Oncol. 2009 Mar;7(1):1-14. Review. http://www.ncbi.nlm.nih.gov/pubmed/19222826


Santoro D et al. Investigation on the association between atopic dermatitis and the development of mycosis fungoides in dogs: a retrospective case-control study. Vet Dermatol. 2007 Apr;18(2):101-106. http://www.ncbi.nlm.nih.gov/pubmed/17355424


Bizikova P et al. Canine cutaneous epitheliotropic T-cell lymphoma with vesiculobullous lesions resembling human bullous mycosis fungoides. Vet Dermatol. 2009 Aug;20(4):281-288. http://www.ncbi.nlm.nih.gov/pubmed/19659540


Affolter VK et al. Indolent cutaneous T-cell lymphoma presenting as cutaneous lymphocytosis in dogs. Vet Dermatol. 2009 Oct;20(5-6):577-85. http://www.ncbi.nlm.nih.gov/pubmed/20178497


Moore PF et al. Canine epitheliotropic cutaneous T-cell lymphoma: an investigation of T-cell receptor immunophenotype, lesion topography and molecular clonality. Vet Dermatol. 2009 Oct;20(5-6):569-576. http://www.ncbi.nlm.nih.gov/pubmed/20178496


Fontaine J et al. Canine cutaneous epitheliotropic T-cell lymphoma: a review of 30 cases. Vet Dermatol. 2010 Jun;21(3):267-275. http://www.ncbi.nlm.nih.gov/pubmed/20141606


Shadduck JA et al. A canine cutaneous lymphoproliferative disease resembling mycosis fungoides in man. Vet Pathol. 1978 Nov;15(6):716-724. http://www.ncbi.nlm.nih.gov/pubmed/751310


Thrall MA etal. Cutaneous lymphosarcoma and leukemia in a dog resembling Sézary syndrome in man. Vet Pathol. 1984 Mar;21(2):182-186. http://www.ncbi.nlm.nih.gov/pubmed/6610244


Fournel-Fleury C et al. Canine T-cell lymphomas: a morphological, immunological, and clinical study of 46 new cases. Vet Pathol. 2002 Jan;39(1):92-109. http://www.ncbi.nlm.nih.gov/pubmed/12102223


Ramos-Vara JA & Miller MA. Immunohistochemical detection of protein gene product 9.5 (PGP 9.5) in canine epitheliotropic T-cell lymphoma (mycosis fungoides). Vet Pathol. 2007 Jan;44(1):74-79. http://www.ncbi.nlm.nih.gov/pubmed/17197626