Sarcoids are the most common skin tumours seen in equids (horses, donkey and zebra). They spread locally in the skin without affecting internal structures of the body. The unfortunate fact is that they spread throughout the skin sometimes reaching a considerable size. As they grow, they may ulcerate and bleed, their presence can cause irritation, interference with tack and loss of value to the affected horse. Sarcoids affect horses of all breeds, colours, age and sex, with a suspected higher incidence in geldings than mares.

It has become apparent recently, that equine sarcoids are associated with infection with bovine papilloma virus (BPV). Very simply, the virus enter the skin cells and can cause a transformation of those cells into tumour cells. Not every horse or donkey infected with this virus will automatically develop sarcoids. Many horses have a strong immunity to the sarcoid virus, thus even if exposed to the pathogen, they will remain sarcoid free. Other horses appear to have a specific genetic (inherited) susceptibility which reduces in fact them immunity with the consequence of developing several sarcoids. Obviously, horses can show different degrees of immunity therefore those with a medium-greater immunity develop fewer sarcoids than those with a medium – low degrees immunity. General rule is that equids genetically susceptible to the virus will develop sarcoids, those genetically resistent will not.
Occasionally, horses suffering from sarcoids can surprisingly develop an immunity so that their sarcoids actually shrink to disappear. A vary rare, but fortunate case when it does!
Sarcoids can occur just about anywhere on the body but are most commonly found on the head, face, ears and eyelid, chest, the underneath of the abdomen and around the sheath.
Flies plays an important rule in the spread of the sarcoids. Evidence for this includes the clinical observation that lesions often develop in area of previous trauma, wounds. This may explain why  susceptible horses that sustain a wound frequently have a sarcoid develop exactly at the site of the wound which it can be confused erroneously, with a proud-flesh (overgrowing granulation tissue). Those wounds never heal whatever you do if a diagnosis is missed. The suggestion is that the open wound attracts flies, some of which are carrying the virus which is deposited at the site.
There are 4 different types of sarcoid. As Professor Derek Knottenbelt says: “each has a different appearance and what you see on the surface may just be the tip of an iceberg with roots of the sarcoid growing down into the deeper tissues”.

  1. Occult: they normally appear as flat, roughly circular hairless area, hyperkeratotic or an area that has altered hair quality. Occult sarcoids can occur at any body site but are rare on the lower leg region. More common in the neck, mouth, eyes, and medial aspect of the forearm and thigh.
  2. Verrucos: sarcoids appear wart-like with an irregular surface. They tend to occur on the face, body, and sheath/groin areas.
  3. Nodular: They are much easier to see and identify, firm, raised nodules under the skin that might or might not have an attachment to the underlying skin tissue. They tend to occur on the sheath/groin areas and the eyelids.
  4. Fibroblastic: irregularly round, raised, firm nodules which resemble proud flesh since they are proliferative, fleshy, and ulcerated lesions. Fibroblastic sarcoids are common at all sites, but usually seen around the groin, lower limbs, coronet, and eyelid. They commonly develop at the site of skin injuries on the limbs.

Horses may, also develop more than one type of sarcoid at any time and may have more than one type in any one area (Mixed Sarcoid). This type of sarcoid is more common in long-standing sarcoid lesions or lesions that have experienced minor trauma.

Most of the time a simple clinical exam will be enough to diagnose the presence of a sarcoid. In other circumstances, a skin biopsy will contribute to the final diagnosis. Vets at Walker Equine Vets are always in contact to Professor Derek Knottenbelt, whom valuable clinical experience is priceless in the effort of approaching sarcoid lesions in the best way and treat them according to the latest protocols.

Several different treatments are described for managing equine sarcoids. Sometimes more than one treatment may be used at the same time. The important thing to remember is that sarcoids have a tendency to recur either at the site of removal or nearby. That needs always to be taken in consideration when you buy a horse with sarcoids, when you want to breed from a mare or a stallion with sarcoids, and, not least, for economical reasons.
The choice of treatment will depend upon several factors:

  • The kind, number and size of sarcoids present
  • The part of the horse affected.
  • Financial considerations.

Conventional surgical removal
This is advised to do when only a solitary tumour is present or there are only a small number present and there is enough free skin left afterwards to close the wound. If there is not enough skin to close the wound, it may be left open to heal by granulation. Tiny sarcoids are often dealt with in this manner. However, approximately 50% of sarcoids treated this way re-grow subsequently.

Applying ligatures or rubber rings
It is possible to remove the bulk of some sarcoids, especially those with a short stalk or neck, by fixing a tight ligature around its base or applying ‘elastrator’ rings. The ligature cuts off the tumour’s blood supply and it dies away or falls off usually 10 days to two weeks later. This method is useful for short-term control of relatively large sarcoids on the inside of the hind limbs or abdomen but does not usually give long-term resolution of the problem. There may be some local swelling after their application but this usually subsides once the sarcoid drops off. This could be combined with other treatments.

Freezing (cryosurgery)
The sarcoid may be frozen by using liquid nitrogen, which causes the tissue to die away. If the sarcoid is large, most of it can be cut away first, leaving only the base to be frozen. This method is more effective at preventing recurrence than surgery alone, but often results in the development of patches of white hair due to damage to hair follicles.

Laser surgery
Where available, surgical laser treatment allows either the bulk of the sarcoid to be removed and the base eroded (burnt away) in one step or the base eroded after de-bulking the main mass. There is minimal bleeding because the tissues are burnt (cauterised), but healing can be slow. Scars will form but hair colour is usually unaffected. Depending on the location of the sarcoids and the behaviour of the horse, this can be carried out either with a standing sedation, or, where not possible, under general anesthesia.

Different forms of radiation therapy have been used to treat sarcoids – usually those around the eye where it is necessary to try to save the eyelid but these can only be used under specially licensed conditions because of the risk of radiation exposure for the operator. In some treatments, radioactive beads or wires may be inserted into the sarcoid or a radioactive source is applied directly to the surface of the tumour.
Recently, a new form of radiotherapy – High Dose Radiation (HDR) has become available for tumours such as sarcoids around the eye. Specialised equipment is used to drive the radioactive source directly into the tumour and there is no risk to the operator due to the way the dose is delivered.

BCG vaccine
BCG is a vaccine produced from the bacterium Mycobacterium bovis for immunisation against tuberculosis. It is injected into the sarcoid tumour(s), often with useful results. Several injections over weeks or months may be required. This treatment is aimed at provoking an immune reaction from the horse’s body to destroy or reject the sarcoid tissue. It is most commonly used for eyelid tumours because, if effective, it allows the eyelid to be saved. A response may not be seen for several weeks after first injection. There is often initial swelling and there may be skin damage following injections and rarely, death has been reported following an anaphylactic shock reaction to the vaccine. Horses to be treated with BCG should receive anti-inflammatory drugs prior to each treatment.

Specially prepared cytotoxic (tissue killing) creams have been widely used to treat sarcoid tumours. These attack the abnormal cells in the sarcoid and are often highly effective, but can also damage healthy tissues. They must be used with great care, especially over bony areas or blood vessels and nerves. They can be used on smaller and flat sarcoids or larger ones after surgical de-bulking. The cream can only be supplied to and used by a veterinary surgeon. Another cytotoxic drug (Cisplatin) is available but must be injected into a sarcoid to be effective. This is another highly specialised technique as dose and pattern of injections varies with size and shape of the sarcoid. Both techniques cause local inflammation and scaring is variable, depending on the size and location of the sarcoids.
It is seldom possible to predict, with accuracy, which treatment will be most successful for the treatment of an individual sarcoid at the start. No matter which treatment option is chosen it can take many months to remove some sarcoids and the effect may not be permanent. Treatment may need to be repeated or changed if new sarcoids appear. Such treatment can be costly.

Should I buy a horse with sarcoids?
In addition to welfare considerations, sarcoids affect the potential value of a horse or pony in two main ways:-

  1. If they interfere with tack or are knocked during exercise, they reduce the ability of that horse or pony to perform. If a mare has sarcoids between her back legs or on her udder they might be knocked or sucked when the foal nurses.
  2. Treatment may not be straightforward and may be expensive if prolonged or repeated treatments are required.

These considerations must be considered against the value of the horse and its other qualities or potentials. It is important to remember that even if treated, there is a good chance that sarcoids will recur.

Sarcoids are much more significant than ‘just a few lumps’ and can be difficult and costly to deal with. If you think your horse or pony may have one or more sarcoids, you should ask your vet for advice. Best results are achieved when a diagnosis is made and appropriate treatment is started early. Scarring is less obvious when the sarcoids are removed or treated when they are small.
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