Sarcoids are a common lesion in horses; in fact, they represent the majority of skin tumors found in horses. Sarcoids can occur as several different types: occult, verrucous, nodular, fibroplastic, or malignant. They are typically found on the lower limbs or face, but can also be on any part of the body. Depending on the type of sarcoid, they can be slow growing or change quickly. For example, occult/flat sarcoids are hairless lesions which are slow growing, but when aggravated can become any of the other types and become more aggressive. Treatment of sarcoids is necessary when they're located in bad locations such as the eye region, lower limbs, or near the saddle region. Malignant sarcoids change very rapidly and thus require aggressive therapy.
Interestingly, Bovine papilloma virus has been shown to be present in up to 88% of sarcoids based on a 2001 study that evaluated 93 sarcoids using PCR (DNA) detection(1). Sarcoids do not seem to be spread from horse to horse, and the underlying cause of sarcoids is still yet to be determined. Sarcoids are known to occur more often in young horses and typically they have more than 1 site affected. Horses in the UK have been reported to have sarcoids numbering over 50 locations on their body!
So how do we treat sarcoids? If they are small or not interfering, we tend to use a wait and see approach. The reoccurence rate of sarcoids after surgical removal can be upwards of 60-70%. Other modalities used include cyrotherapy (liquid nitrogen), laser excision, radiation, immune-mediated approaches, intra-lesional chemotherapeutics, and topical therapies. Still further options include autologous vaccines and autologous implantation
(2). We have used the implantation in our practice but reserve it for aggressive sarcoid control. There are a lot of options to attempt to treat sarcoids, but reoccurrence is still a major issue. Topical therapies include Aldara (Imiquimod), Acyclovir cream, and Xxterra. Xxterra is still commonly used but is extremely caustic and most horses resent it after only a few treatments. Many horses have become incredibly ear shy due to caustic topicals used for sarcoids in/around the ear region. Aldara application still has an inflammatory component, but as an immune response modifier it can be helpful for small sarcoids. Acyclovir cream is an anti-viral, and we have had great success with using it without pain/discomfort from our patients. Complete regression can take several months of frequent applications.
We hope this information is helpful and as always, feel free to call us with questions!
Reference:
1. A. MARTENS, A. DE MOOR, R. DUCATELLE,
PCR Detection of Bovine Papilloma Virus DNA in Superficial Swabs and Scrapings from Equine Sarcoids, The Veterinary Journal,Volume 161, Issue 3, 2001
2. How to Treat Equine Sarcoids by Autologous Implantation; Dr. Ben Epsy, 2008 Vol. 54 AAEP PROCEEDINGS