| Sarcoids - Know Your Enemy |
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By Stephen Champion, BSc (Hons) BVM&S MRCVS, The equine sarcoid has been the blight of horses, their owners and their vets for generations. It is likely to be the commonest skin cause of euthanasia in horses and constitutes a serious economic loss to the equine industry. On an individual basis they can be a cause of considerable pain and suffering to horses, heartache to their owners and frustration (and embarrassment) to their vets! What is a Sarcoid? Known formerly rather innocuously as the equine “wart”, the sarcoid is a skin “lesion” occurring singly or in multiples usually on the head, groin or the axilla (armpits) of horses. The term “lesion” is used generally here, although the term “skin cancer” is perhaps helpful to emphasise the severity of the disease. They can appear over a variable period of time and in six distinct forms, such that in some cases they can be difficult to diagnose. There are many different types of skin disease in horses and I would advise that the majority should be checked by your vet, since they can be confusing to identify. If a sarcoid is suspected, your vet may advise that a biopsy is taken and sent to a lab for identification. However, biopsies may not be necessary and the diagnosis can often be made on appearance and location alone. So, who gets sarcoids? Horses of all breeds, ages and gender can develop sarcoids. However, we know from various studies than geldings are more prone than stallions (especially around castration wounds). They are most common in horses between the ages of two and six years old. Appaloosas, Arabs and Quarterhorses are more at risk than Thoroughbreds and Standardbreds are at lower risk than Thoroughbreds. What causes sarcoids? Amazingly, after years of research and investigation, the veterinary profession is not absolutely sure. A strong contender for the causative “agent” is the bovine (cow) papilloma-virus. However, to my knowledge, no virus has ever been isolated from a sarcoid. Furthermore, if this virus is injected into the horse skin, a lesion resembling a sarcoid is formed. However, the horse forms antibodies against this virus and the lesion disappears – which is not the situation with a naturally occurring sarcoid! Some circumstantial evidence suggests that biting flies may be involved in transmission of the disease. This may explain why patterns of the disease vary in different countries and why in some countries (but not here) the disease is regarded as contagious. What do they look like, then? As mentioned above, there are six distinct forms of the sarcoid, so distinct in appearance that it is often hard to justify the inclusion in the same “disease”. Each shall be briefly described, although it should be remembered that each looks like several other unrelated diseases, so don’t panic just yet, but get it checked! The Occult Sarcoid: nothing to do with the “Exorcist”, this is a circular patch of hair loss with a grey, scaly surface. It doesn’t cause the bed to spin around, but it is serious and looks very similar to ringworm or tack rubs or lice infestation. The Verrucous Sarcoid: looks a little like the above, grey and scaly, but extends deeper into the skin and is more irregular in outline. It can be mistaken for a variety of viral skin diseases and a tumour called squamous cell carcinoma, which is a real nasty! The name reminds you of school swimming trips. The Nodular Sarcoid: these are mainly under the skin, forming round nodules with apparently intact (but often thin and shiny) skin overlying. They are usually found around the eyelids and in the groin and look like a variety of skin tumours, including typical melanomas in greys. The Fibroblastic Sarcoid: these are nasty and aggressive and look like true ulcerated skin tumours. They can often start after injuries to the skin, especially on the legs or after surgical removal (or biopsy!) of other forms of sarcoid elsewhere. They look horrific and can be pudunculated (on stalks) or very invasive into the surrounding skin and deeper tissues. They can look like “proud flesh” initially, on a healing wound, so beware. I hate these and generally run away….. The Mixed Sarcoid: like the pudding trolley of a dubious restaurant, a platter of suspicious-looking but vaguely-familiar nasties (as described above), of different ages, all jostling unattractively for position. May be occult, nodular and fibroblastic sarcoids all in there together. The Malevolent Sarcoid: a sarcoid behaving like an aggressive tumour by spreading along lymph vessels* forming other masses along these vessels and in local lymph nodes*. These often develop following surgery on fibroblastic sarcoids (poor horse…poor owner….poor vet!!). *The lymphatic system protects the body from infection by draining tissues through a serious of vessels and nodes. Common to most of the above, is well known that sarcoids can transform from a less to a more aggressive form, especially after trauma or attempts at surgery. They tend to persist or change for the worst over time and only very rarely resolve. It is recognised that they may re-occur years after removal in the same or other sites. So what can we do about them, then? Treatment options are diverse in approach, suggesting that none is entirely satisfactory – which is the case. Failure and re-occurrence is common (and disappointing and often expensive). Selection of the correct treatment is essential and sometimes if the lesions are small and few in number they are best left alone, so long as they do not interfere with locomotion. The most popular treatment methods currently available shall be summarised below. Please, please be aware however, that the chances are your own vet, with his/her knowledge of your horse, is best placed to decide on appropriate treatments. Many times I have been faced with a horse owner and a magazine article, written by some well-meaning contributer... Surgical removal: fraught with potential for regrowth (even 15 years later!), with 90% of the re-grown lesions being more nasty. Perhaps only a 15-20% success rate overall. Mixed sarcoids are particularly prone to re-growth and generally only small nodular sarcoids with well-defined edges may be attempted. Furthermore, sarcoids in areas such as the eyelid and lower leg may be particularly difficult to remove surgically. I have had some successes, and to be honest some failures, and usually avoid it like the plague if I can. Cryosurgery: freezing, with perhaps only a 20-25% success rate. It works best on small, well-defined lesions but requires most of the mass to be removed surgically first and needs a long general anaesthetic, which horses object to! Immune-mediated therapy: currently this takes two main forms. Firstly, making an “autogenous vaccine” from the horse’s own lesions, and injecting it back into the horse. This is fraught with disaster (I have never used it, thankfully) and may cause dramatic spread to other areas of the skin. Secondly, the use of BCG cell-wall extracts has enjoyed some success. The injection has an effect only on the lesions into which it is injected and the injections need to be repeated over several weeks at reducing frequency. I have found it useful but a real fiddle and considerable cost due to the need for repeated injections and the variable results obtained. Furthermore there is a genuine risk of anaphylactic shock and so the horse has to be pre-medicated with anti-inflammatory drugs, which adds to the cost. It can be very useful for sarcoids around the eye where very precise treatment is required. Radiation therapy: this modality using such radiation sources as iridium 192 has proven highly successful, particularly in the treatment of sarcoids around the eye, with success rate of 98% reported from one study at Liverpool University. The treatment generally leaves very acceptable cosmetic results although it is expensive and success is limited by the size of the sarcoid. Topical / Intra-lesional chemotherapy: vets have been attempting to treat sarcoids by slapping on highly toxic chemicals for over a hundred years. Liverpool University, under the guidance of Dr. Derek Knottenbelt, has developed a topical (surface application) treatment called AW4-LUDES. This consists of a number of “heavy metal” salts in combination with compounds preventing cell division. It is available to veterinary surgeons in private practice but only on an individual case basis and under strict guidelines. It is applied (and sometimes injected intra-lesionally) usually every 72 hours for 3 or 4 occasions to individual sarcoids and causes rapid cell death. The sarcoid usually “falls off” at any stage between 2 days and several weeks after treatment is complete, but can cause considerable inflammation during the process and scarring afterwards. A resolution rate of 80% is quoted and my experiences would concur with that. I have experienced some re-occurrence at the site and found that horses can become quite sore during the inflammation phase. These horses have often required courses of oral painkillers (usually “Bute”) and occasionally antibiotics if the inflammed lesions have become infected. And, in summary... Sarcoids are never good news, but then again, neither are many of the diseases they can get confused with. If your horse has skin disease, and you don’t know what it is (especially if you have tried treatment, eg. for lice, and it has failed) then get it checked by a vet. Any sarcoid should be given a guarded prognosis, because they often transform into a more aggressive form, they rarely resolve by themselves, and the treatment options currently available are unreliable. Try never to by a horse with sarcoids as you are likely to be buying a lot of trouble. Your vet will point them out to you during / after the pre-purchase examination (the“vetting”) and will likely express his reservations! Remember that sarcoids are not warts and are probably most helpfully described as “skin cancer”. The treatment options at present are limited and the ideal treatment has not been found. The cytotoxic cream from Liverpool is probably in general terms the most versatile, efficacious and cost effective available at present although by no means a panacea. Any thoughts of prevention must wait until a definitive cause has been discovered; in the meantime, fingers crossed and keep the flies off! |
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