By Vicky Rowlands Cert. EP MRCVS – Ashbrook Equine Hospital, Cheshire.
Sarcoids are a type of equine skin tumour that exist in the skin and the tissue layers immediately below the skin. They do not spread to internal organs. Unfortunately, we now recognise 2-8 % of horses in the UK have sarcoids. Interestingly, Europe seems to have a lower rate of sarcoids in their equine population. As sarcoids affect all equines, it means even some of the best competition horses have them and if sarcoids do not affect tack areas or vision, competitive careers should be unaffected. It seems sarcoids commonly develop between 2-10 years of age although they can occur at any time from a few weeks of age to geriatrics.
There appears to be a genetic predisposition that dictates which horses develop sarcoids when exposed to the disease. Lipizzaners seem to be very resistant to sarcoids; Arabian horses seem more susceptible. Despite the apparent genetic predisposition and familial links, it is unknown whether predisposition to sarcoid development is a heritable factor. Unfortunately, there are still so many unanswered questions with regard to sarcoids. It does appear that bovine papilloma virus (BPV) may be implicated in some way but it is certainly not the whole story. Sarcoids also seem to spread during the summer which we attribute to spread of a viral factor by flies, to susceptible skin tissue; either on the same animal or different animals. Most sarcoids appear on thin skinned areas that are often targeted by flies, such as head, belly, and groin. Sarcoids can also occur at wound sites so it should be considered if a wound is non-healing.
There are six different types of sarcoid that that we recognise:
Occult – These sarcoids are often confused with ringworm as they are roughly circular patches of hairless skin with tiny nodules.
Verrucose – These are also sometimes confused with ringworm or rubs as they have a grey, slightly warty appearance.
Nodular – These are classic skin lumps that are often covered with a thin layer of normal skin.
Fibroblastic – These are also easily recognisable as fleshy lumps that have a pink or red surface which bleed easily. These may be termed as angleberries by some more traditional horsemen.
Mixed Sarcoids – They are classed as mixed if they have two or more types of sarcoid tissue identifiable in the lesion.
- Malignant – This is the rarest and most aggressive type of sarcoid and can spread rapidly through the surrounding skin. There are more malignant sarcoids identified in the UK than in other countries.
Once a horse has one sarcoid, it will usually develop more. Sarcoids will grow over time; sometimes this will be very rapid and sometimes there will be no change for many years. Unfortunately, there is no definite way to predict how each individual sarcoid will behave. Very rarely, a sarcoid will spontaneously resolve. When aggravated or treated inappropriately, it is recognised that sarcoids can change from quiescent lesions to highly aggressive forms.
The effects of sarcoids
Sarcoids are primarily problematical when they are in difficult locations such as around the eyes, over areas that can be rubbed by tack or on a joint. Sarcoids around the eye are particularly difficult to manage as they often have roots that penetrate the eyelid muscles. Treatment of these can occasionally endanger the horse’s vision. Sarcoids will affect the cosmetic appearance of the horse so potentially preclude it from a showing career. This will also often be reflected in the purchase price of a horse. Even horses with a single sarcoid will often develop more, so treatment for this should be budgeted for. Rarely, sarcoids can become infected and cause the horse to be systemically unwell.
Sarcoids are often diagnosed on their appearance. Whilst biopsies are diagnostic, they can stimulate a relatively non-aggressive sarcoid to become highly active and aggressive. It is for this reason that the best treatment for a sarcoid is the first one; applying non-prescribed treatments can result in very nasty effects, making it harder to resolve!
The fact that there are over 40 recorded treatments for sarcoids suggests there is no single failsafe treatment. Below we briefly discuss some of the more commonly chosen treatments.
This may be the best option for a sarcoid that does not change for many years, although predicting this is obviously difficult. Whenever this method is chosen, if the sarcoid changes or multiplies then an alternative must be sought. This may be appropriate during summer as we often start treatment in the cooler months when flies will not affect healing wounds after treatment. If this is chosen, then scrupulous fly control should minimise the risks of spread on the same horse and to others.
Surgical removal – Unfortunately, although this is probably one of the most cost effective treatments, it must be undertaken with extreme caution as the chance of ‘seeding’ sarcoid tissue is very high. It can be very difficult to obtain large enough margins to eliminate the risk of recurrence.
Laser removal – This is very commonly recommended and seems to have very high success rates. Like surgical removal, the horse has much less to contend with – he is sedated, the area is anaesthetised and a ‘cutting’ laser used to remove the sarcoid. The laser acts to ablate (kill) any cells on the surgery margins and prevent recurrence. Laser also makes the surgery a relatively bloodless procedure. After this, the wound is left open and will heal over the following weeks.
Ligation – This is often achieved with a lamb castration ring but can be very variable and highly inappropriate if there is a deep root to the structure. It should certainly only ever be done by a veterinary surgeon and attempts using string or tail hair can worsen the lesion and make it harder to treat.
AW5 cream – The predecessor of this was known as Liverpool cream and is only available from Equine Medical Solutions via a referring vet. As this cream is a topical chemotherapy agent, it can only be applied by a vet, usually over 3-5 visits. It can be painful for the horse and the sarcoid can take a long time to fall off. The benefit of this treatment is, like laser, it has a high cure rate with limited recurrence recorded.
Efudix – This cream can be used prior to other treatments such as laser removal and is most commonly prescribed for occult or verrucose types. It is applied 2-3 times daily and can be quite painful for the horse, making applying it rather hard!
Aldara (Imiquimod) – This is only used on small sarcoids, again under veterinary prescription. It can be very expensive and difficult to handle.
Other topical treatments that are used as adjunctive, not stand alone, treatments are bleomycin, blood root ointment, zorac or acyclovir.
BCG is hard to obtain but can be very effective for sarcoids around the eye. It is injected into the sarcoid by a vet, usually over 3-7 visits. The horse can exhibit an extreme allergic reaction after injection so it is carefully monitored immediately after treatment. This method is safe for the actual eye and leaves minimal scarring after successful resolution. Interestingly, if this is used on limb sarcoids it will dramatically worsen them.
This is not used very often due to the cost and dangers of handling medications such as this but can be very effective. Drugs injected into sarcoids include cisplatin, mitomycin C or 5 fluoro-uracil.
Again, this is a very specialised procedure with important health and safety and financial considerations. It can be very effective, especially for sarcoids around the eye but it is only available in a very limited number of centres throughout the world.
This is now offered at very select hospitals and reduces the risk to humans of traditional iridium radiation treatments. It is mainly being used for ocular sarcoids or other tumours in this location and shows great promise.
This involves using a topical or systemic agent that makes the sarcoid tissue sensitive to a certain wavelength of light. Again, this is available from a limited number of specialists.