Dr. Patricia Provost
Skin problems in the horse are very common, but most are harmless lumps and bumps. Rarely do skin problems require aggressive investigation like biopsy, and many are self-limiting. However, certain skin problems or lesions require prompt attention and a thorough diagnostic approach, since they pose a serious threat to health. The use of anti-neoplastic agents (e.g. cisplatinum) applied topically or injected directly into the tissue
Sarcoids, which are tumors, are notable for their unpredictable behavior, and although they look harmless at first, they can spread and cause a lot of damage. The sarcoid is the most common tumor of horses, and it is unique to the horse.
Sarcoids only affect the skin, unlike some tumors of the skin, like melanomas and squamous cell carcinomas that spread widely. They are caused by a virus that is thought to enter the skin through traumatized areas and as such, can occur at sites of skin bites or in healing wounds.
Sarcoids can occur in horses of any age but most cases will initially develop in horses less than 7 years of age. Although they have been reported in nearly every breed, genetic studies have shown that some families and breeds of horses may be more at risk of developing the tumor.
The tumor most commonly develops on the head, neck, limbs, or ventral abdomen. Tumor lesions (1 cm to >20 cm in diameter) can be solitary, or multiple in number, and they appear as hairless, thickened areas of skin, as flesh-like growths, as large firm masses within the skin, or as wart-like growths.
Unlike many other tumors, sarcoids do not spread (metastasize) through the body but they can grow aggressively at the site in which they originate. They develop like the roots of trees, projections in the skin that far exceed the size of the visible or palpable mass. These "roots" are in part why sarcoids are difficult to cure.
Lesions, depending on their location, type and growth rate may have little impact (outside of being a cosmetic blemish) on the affected horse or may, in severe cases, result in loss of use of the horse or its death.
A tentative diagnosis can be made by the characteristic appearance of the tumor, its location and on its history of development.
Its appearance can look very similar to other skin lesions including, but not limited to, proud flesh (excessive granulation tissue), squamous cell carcinoma, habronemiasis, fibrosarcoma, intradermal melanoma, scar tissue, and warts.
A definitive diagnosis requires that a tissue biopsy be obtained and evaluated by a veterinary pathologist.
Treatment is tailored to the patient but generally involves surgical removal of the lesion followed by ancillary treatment of the remaining surrounding skin. Ancillary treatments include
Freezing the tissue with liquid nitrogen (cryotherapy)
Injection of the tissue with an immune stimulant
A series of biweekly to monthly treatments is often required to be successful. It is very important to attack the tumor aggressively at the onset, as failure to do so often results in growth of a more resistant sarcoid tumor.
Tumor treatment should be pursued only if the horse has a current tetanus vaccination or is given one simultaneously. Antibiotics may also be administered to prevent against bacterial infection during tumor necrosis (death) and wound healing.
The chance for a successful outcome is always increased if treatment is started when the size of the tumor is small. Don't wait and see if the tumor disappears on its own.
The type of post-treatment care a horse requires is based on the location of the lesion and the method of treatment. Open wounds often require bandaging to keep the area clean and protected from flies, and topical antibiotics may or may not be recommended.
If the area is bandaged, bandages usually need to be changed every day to every other day, at least initially. It may also be necessary to confine the horse to a stall to restrict his exercise. This is especially important if the wound is over or adjacent to a highly mobile area of the leg or body. Exercise only prolongs the duration of healing of these types of wounds. Immobilization of the wound area with a splint, in addition to a bandage, may also be required in some cases.
Wounds that are sutured should be kept clean and dry for 2 to 3 weeks. Sutures or skin staples will be removed at 10 to 14 days. Wounds that are not sutured should have the skin surrounding them cleaned once to several times a day to prevent irritation from the fluid discharge from the wound.
Cleaning the surface of the open wound is dependent on the original method of treatment. In some cases very gentle cleansing with warm water is required, while in other cases this is contraindicated.
Continuation of oral or injectable antibiotics may be necessary for a short period of time.
There is currently no method or vaccine available to prevent the occurrence of a sarcoid. The best advice is to make sure that your horse lives in a safe environment to minimize his chance of getting a skin injury that may then become an entry site for the virus.
Horses that have had a previous sarcoids are at risk to develop a sarcoid in the future. Always bring to the attention of your veterinarian the presence of skin masses or changes in skin thickness, skin texture, or haircoat in your horse.