Some thoughts on epitheliotropic lymphoma- a rare disease in veterinary dermatology

Epitheliotropic lymphoma is an uncommon tumour in veterinary dermatology. I think our little survey at the beginning of our veterinary webinar proved that you know if we’d have been talking about mass cells I think we all would have seen one or two cases of mass cell tumour, at least within the last 12 months. But there was obviously 40% of you who had not seen this at all this year. Mycosis fungoides is the most common form and the name comes from the Greek mykes which means fungus and eidos informs and that was because the French dermatologist Albert who discovered this in 1906 in humans felt that it looked mycological at first and then towards the end as the nodules appeared they were almost epitumurous they also looked fungal in nature. So he gave it that name of mycosis fungoides. I hope my Greek for any Greeks reading is close enough to the correct spelling. Obviously, it is mainly seen in older dogs and cats in veterinary dermatology although I have seen it in an English Bull Terrier that was only four years old. It may follow on from alopecia mucinosa in cats. There were two cases of alopecia mucinosa that then developed into full blow mycosis fungoides. There is no obvious sex or breed predisposition. I have seen it in quite a lot of Labradors and Retrievers but of course Labradors and Retrievers are quite a common breed anyway. So the literature really doesn’t seem to show any breed predispositions. Aetiopathogenesis is unknown in dogs and cats although unfortunately FeLV as it gets blamed for everything else has been blamed as a possible cause of epitheliotropic lymphoma in cats. In humans, we do have a T cell lymphotropic virus type 1 that’s been implicated and unlike B cell lymphomas which are I think quite chemotherapy sensitive cutaneous T cell lymphomas don’t really seem to ever be cured. And one of the theories of the aetiopathogenesis is that there is a chronic antigenic stimuli of the skin T cells and over time this becomes not only reactive but neoplastic. And the kind of work behind that was that in human forms they were looking at … the doctors were looking at chronic antigenic stimulation by pathogens such as Helicobacter and Hep C virus and they found that these were occasionally then converting into gastric mucosal and non-Hodgkin’s Lymphoma tumors. There is a similar role in human dermatology being prescribed to staphylococcusaureus. Again, a sort of chronic antigenic stimulation of the skin T cells leading to the formation of epitheliotropic lymphoma. So that is something that is considered as a possible aetiology and we can see that … we’ll discuss this in a bit more detail later but one of the subclasses of dogs that we see with epitheliotropic lymphoma are those old, atopic dogs that have gone on and on with atopic disease you’ve never really been able to clear them and then suddenly they go a lot worse. That is a dog that’s changing from being an atopic dog to a dog potentially with epitheliotropic lymphoma. At the Hong Kong World Veterinary Dermatology Congress Peter Moore and VerenaAffolter who are two of the world’s experts on lymphocytic and histiocytic diseases published a study going back from 1985 to 2005 and they looked at 56 dogs with epitheliotropic lymphoma and they found that 39 of those had mycosis fungoides, 16 had pagetoidreticulosis and only one had Sezary Syndrome. They also looked then at the markers on the T helper cells and they found that in dogs the markers tended to be CD8 and T cell receptor gamma delta in the canine epitheliotropic lymphoma. Whereas, the human epitheliotropic lymphoma is CD4 and T cell receptor alpha beta and the thought on that was that it showed that there were maybe slightly different reasons for why the disease formed and you know obviously slightly different treatments might be necessary. Other work that’s been done on aetiopathogenesis has shown that advanced epitheliotropic lymphoma patients are very immunosuppressed. There is a Th2 skewing of T cells by IL 4, 5 and 18 which is moving them into Th2 type diseases. Th2 type diseases include atopy and we find that these particular IL are skewing the dog into a Th2 response. In fact we know that if we can use cytokines such as IFN gamma and IL12 which actually try to promote Th1 responses then they can help in treatment. So we know that this disease is a Th2 disease and we also know that aggressive cases of this disease can happen when we try to inhibit one of the Th1 cytokines and tumour necrosis factor alpha. These interesting facts are really helping us to understand this very important disease in veterinary dermatology