What’s that bump? Equine Sarcoid By Brian S. Burks, D.V.M., Diplomate American Board of Practitioners (Equine) Have you ever noticed any lumps or bumps in the skin of your horse? If so, you should have these evaluated by your veterinarian. These can range from innocuous bug bites to bacterial/fungal diseases, or skin tumors. The sarcoid is the most common skin tumor in the horse. Their behavior is completely unpredictable. They can be ‘silent’ for many years and then suddenly begin to grow quite rapidly. Sarcoids tend to be locally aggressive, but seldom spread from one site to another; even though they do not spread, they can become quite deep, involving the underlying soft tissue and bone. They do not spread to internal organs. The etiology of the equine sarcoid is unknown. It has been said that a bovine (cattle) papilloma virus is the cause, and their DNA has been found in the sarcoid, but no active virus has ever been found. Other types of viruses have also been proposed. Sarcoid types include the occult, verrucous, nodular, fibroblastic forms, and mixed sarcoid, containing features of several of the tumor types. The occult form occurs mainly in thin haired areas and is fairly flat. They occasionally open and drain. They may only show small areas of hair loss initially, before becoming an overt tumor. Verrucous sarcoids are a bit larger and form more crusts. They have local skin thickening around the main area, indicative of further tissue invasion. Nodular sarcoids are large, firm masses in the skin and subcutaneous tissues. The last type, the fibroblastic sarcoid is much larger and appears similar to exuberant granulation tissue, or proud flesh. These tumors are quite vascular, and bleed easily. They may be pedunculated or have a larger base. It usually develops at the site of a wound, especially on the limb. Many times these various tumor types are mixed, with occult and verrucous and nodular forms all occurring together. Differential diagnoses include papillomatosis (warts), chronic blistering, hyperkeratosis (thickened skin from something like sweet itch), equine sarcoidosis (granuloma) exuberant granulations tissue, and squamous cell carcinoma. Sarcoids most closely resemble exuberant granulation tissue. All skin tumors should be sampled and sent for histopathology to determine the type of tumor and distinguish sarcoids from granulation tissue or other infections. Histopathology also allows assessment of the margins, to determine if the entire tumor was removed. Simple removal tends to make sarcoid tumors much more aggressive, so that they will enlarge rapidly. This is because the entire tumor has not been removed due to its invasion of surrounding skin. Treatment modalities are many, and only very rarely do these tumors resolve on their own. Cryotherapy (freezing with liquid nitrogen) immunologic treatment with BCG or Eqstim, and repeated intra-lesional injection with cisplatin, bleomycin, and 5- fluorouracil (5-FU) have all been used. Cisplatin and 5-FU are the most successful. Currently, sarcoids may be implanted with cisplatin beads, to allow a longer exposure time of the tumor to the cisplatin. Another way to administer cisplatin is via electro-chemotherapeutic poration. This equipment opens the cell membranes to cisplatin, allowing more of this chemotherapeutic agent to get inside the cell to effect cell death. Unfortunately, the expense of the equipment severely restricts its use. Bleomycin is another such agent, but it has not shown much success. Other topical anti-tumor medications have also been used, with varying success, including Aldara and XXTERA. The latter, in some cases, may transform the tumor, making it much more aggressive. Also transplanting some of the tumor to a distant site in the horse has been used, with the thought of immunizing the patient to the tumor; this has enjoyed only limited success. I personally have the best result using a surgical laser combined with cisplatin and sometimes 5-fluorouracil. This removes most of the tumor, destroys cells several millimeters beyond what the eye can see, and leaves medication locally to kill any tumor cells that may remain. If the tumor is able to be completely removed via excision (usually only small lesions) this is best, and is considered curative. Refractory cases can be treated with local radiation therapy with Iridium 192, known as interstitial brachytherapy, by implanting radioactive beads in the tissue. The beads are left in until a pre-determined dose is reached. Patients must be quarantined while the radioactive implants are in place, restricting this modality to a few referral centers. The success rate approaches 100%. These tumors are less ably treated by Teletherapy or Tomotherapy (this combines a CT with Teletherapy) an external radiation beam, which requires specialized equipment and repeated general anesthesia and enjoys a success rate of less than 30%. Thus, the equine sarcoid is the most common skin tumor in the horse. Fortunately, although it can be locally aggressive, it normally does not spread to distant sites (metastasize). There are several different types of sarcoid that vary in appearance, and may be confused with other types of lesions, including other tumor types. Simple surgical removal or biopsy is not recommended because this tends to make sarcoid tumors extremely aggressive, growing very quickly, and spreading through the local tissue. Removal with an Nd:YAG laser, combined with local anti-tumor medication gives the best success rates, although very occasionally some tumors may persist. Brachytherapy is the most successful treatment modality for refractory tumors, but requires specialized centers. You and your horse should seek treatment for any mass that is actively growing. Dr. Brian Burks is the owner/veterinarian at Fox Run Equine Center, a 24-hour medical-surgical center near Pittsburgh, Pennsylvania. He is board certified by the American Board of Veterinary Practitioners (Equine Practice). This certifies him as an expert in all categories of equine practice. foxrunrequine, [email protected] Fox Run Equine Center :) :)
Posted on: Mon, 07 Apr 2014 16:00:05 +0000
Trending Topics
Recently Viewed Topics
© 2015