Equine Sarcoids –Consistently Unpredictable

by Tom Righton. HNVG Director, BVSc, MRCVS

Sarcoids have posed a treatment challenge for veterinary surgeons for as long as they have been recognised, due in no small part to their unpredictable behaviour and variety of clinical presentations. Consequently, no single treatment is reliable in dealing with all sarcoids and, there is a wide range of options available; every case is different requiring assessment and careful consideration of all the factors before embarking on treatment. That said, the introduction of surgical lasers is proving a very useful resource with some significant advantages in certain cases, although an understanding of the different types and behaviour of sarcoids is essential in their selection.

Sarcoids are the most common type of equine skin tumour, estimates of their prevalence vary, a recent study reported a frequency of 5.8% within the population of horses in Great Britain. They are locally invasive and aggressive, however they do not metastasise to internal organs. Their behaviour is variable, some progress rapidly while others remain unchanged for a lengthy period then suddenly start growing, frequently after trauma or irritation to the sarcoid. Inappropriate treatments and home remedies can also lead to their rapid spread and growth. Rarely, spontaneous resolution occurs and thereafter, the horse will usually be immune to further sarcoids. Unfortunately, this starkly contrasts with horses that are treated; even with successful treatment a horse which has had sarcoids remains at risk of developing more at other sites. Sarcoids may develop anywhere on the horse’s skin; most commonly seen on the chest and axilla, groin and sheath and, on the face around the eyes and muzzle. These areas are frequently bothered by flies, and it is thought that they may have a role in the spread of sarcoids across the horse. For horse owners sarcoids have a significant economic impact, treatment can be costly and ongoing, can require time away from work or competition, horses with severe extensive lesions may not be able to work and, horses are devalued significantly at sale and sometimes failed at pre purchase examinations due to the presence of sarcoids.

The role of lasers

Surgical diode lasers are increasingly being used in veterinary practice as a treatment modality, this is likely due to the increased availability of the technology and, an increase in the evidence base supporting their use in appropriate cases. There are three main types of laser currently in use; CO2 lasers heat up the water within the tissue causing less trauma to surrounding tissue, diode and Nd:YAG lasers are both delivered via a fibre, and achieve better coagulation of blood vessels. Laser light provides a highly focused beam of energy, which generates intense heat when it interacts with tissue causing vaporisation of the tissue at which it is directed. Blood vessels are coagulated leading to a bloodless surgical field.

Traditional surgical excision with a scalpel blade and closure of the wound by stitching the wound edges back together has been associated with poorer success rates, it is thought that sarcoids seed tumour cells into the wound bed as they are removed, frequently leading to regrowth at the scar site.

With laser surgery these cells are vaporised as the sarcoid is removed, and this is likely one of the reasons why excision by laser surgery is proving more successful than traditional excision. The energy provided by laser light is extremely accurate and can be directed with great precision, the energy dissipates quickly within tissue causing reduced post- operative swelling and pain, compared to thermocautery (in which an electric current is passed through a resistant wire generating heat, which is then applied to the tissue).

Treatment

An assessment is made based upon the size, location and number of sarcoids present, and a surgical plan is made.

In many cases the sarcoids can be removed with the horse under standing sedation in combination with local anaesthetic and pain relief. If however, the sarcoids are not accessible or the patient is particularly fractious, it may be necessary to administer a general anaesthetic. The sarcoid is removed along with a minimum of a 1cm margin of healthy surrounding tissue to try to ensure all the root has been removed. The wound will therefore, often appear significantly larger than the sarcoid that was present. It is generally advised that the sarcoid is submitted for histopathology to confirm the diagnosis and, to ensure that surgical margins have been achieved. The wound is left open to heal by granulation, the time taken for healing depends upon the size and location of the wound, however most are typically healed in 4 - 8 weeks.

Many patients will be discharged the same day, while others may spend one night at the surgery if they have had a longer procedure or general anaesthetic. All horses are discharged with a course of anti-inflammatory medication such as phenylbutazone, to help reduce pain and swelling. As long as conditions are not very muddy and there are not lots of flies around, horses are typically turned out for paddock rest as movement helps to reduce post-operative swelling.

Antibiotics are not generally prescribed, the surgical site is given a sterile scrub prior to surgery and the intense heat from the laser serves to sterilize it further.

After a post-operative check about 7-10 days after surgery, most horses do not need further review and can begin work providing the tack does not interfere with wound healing.

A study by P Compston et al published in 2015 looked at a large number of horses, which had sarcoids treated by laser surgery. It reported that 82% of sarcoids removed did not come back and that in horses which had multiple sarcoids removed, there was no recurrence in 71% of cases. The same study also found that recurrence of the sarcoid at the surgery site was most likely to occur within 6 months. Verrucose sarcoids had higher chances of recurring, possibly due to a wider root network of sarcoid tissue than other sarcoids.

It has been shown that there is a less successful outcome in the treatment of sarcoids in cases that have previously been unsuccessfully treated with home preparations. This may be because interfering with sarcoids unsuccessfully leads to them behaving more aggressively or, that previous treatments disrupt the margins of the sarcoid making it more difficult to

ABOUT THE AUTHOR: Tom Righton,

HNVG Director, BVSc, MRCVS

Tom joined Hook Norton Veterinary Group in 2014 and the Practice Partnership in 2022. Having previously worked in a mixed practice in Worcestershire, Tom joined us to work solely with our Equine Team. Tom has specialist interests in orthopaedic & lameness cases and is one of the key vets for laser surgery and sarcoid removal.

establish surgical margins.

Instances when laser surgery may not be appropriate include perioccular sarcoids, where proximity to the structures of the eye means that surgical margins cannot be achieved. Malevolent sarcoids covering an extensive area with indistinct margins are often too extensive for the entire area to be treated.

There is currently no one treatment that is safe, effective and practical that can be used in all cases of equine sarcoid. An assessment of the type, size and location of the sarcoid is essential before beginning treatment. Treating sarcoids with non-prescription treatments can lead to rapid change or growth in the sarcoid and, may make future treatments less successful. If in doubt actively monitoring the size and behaviour of the sarcoid before getting a veterinary assessment is preferred.

Laser surgery is a very useful tool in the treatment of a wide range of equine sarcoids, it is generally very well tolerated by horses and has a favourable success rate when compared to many other treatments with relatively few complications however, wound healing can take time.

Tom is also currently studying for his advanced practitioner certificate in Equine Orthopaedics at the University of Liverpool, alongside his work at HNVG.

Tom has a young family, and his wife, Lotty, is a Vet in our Small Animal Team. Tom enjoys getting out into the countryside on his road and mountain bikes and following the National Hunt Racing & Point to Point seasons in his spare time.

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