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Management of sarcoids

Numerous treatment options are available but there are many considerations to take into account

02 November 2020, at 8:30am

Sarcoids are locally aggressive fibroblastic cutaneous skin tumours which can occur anywhere on the horse’s body. However, their predilection sites are the axilla, inguinal region, ear, periocular region and the penile sheath. They are the commonest cutaneous neoplasm in horses affecting up to 6 percent of horses in the UK (Ireland et al., 2013), with all ages of horses affected. If a horse has one sarcoid it is predisposed to getting more. Rarely, they can spontaneously resolve and it is this trait which has likely led to multiple anecdotal reports of success with otherwise completely unproven treatments. This can be dangerous as a failed treatment or trauma can trigger more aggressive behaviour of the sarcoid. If the sarcoids are extensive they can debilitate and metabolically exhaust the horse and, in some locations (eg the eyelids), they can cause important functional problems; in these locations, treatments can be limited. Sarcoids can also affect the commercial value of a horse.

The diagnosis of sarcoids is largely based on clinical appearance. A biopsy can be taken to confirm the diagnosis but this risks aggravation resulting in transformation to a more aggressive type. There are six different types of sarcoid (Table 1; Knottenbelt, 2005).

TABLE (1) There are six different types of sarcoid (Knottenbelt, 2005)
TABLE (1) There are six different types of sarcoid (Knottenbelt, 2005)

Treatment options

As with all neoplasms, early treatment is more successful and broadens the possible treatment options.

Benign neglect

This can be tempting with a very small and insignificant sarcoid, usually an occult or verrucose type. If this approach is adopted, very careful monitoring is required as sarcoids can rapidly progress, especially with trauma. It should be borne in mind that treatment when smaller results in reduced morbidity and costs, and improves outcomes.

Ligation

This is usually performed using elastrator rings. It works well provided there is no extension of the sarcoid below the ring. The suitable sarcoids are type A1 and B1 nodular sarcoids and type 1a fibroblastic sarcoids. This can be combined with topical or intralesional chemotherapy.

Topical chemotherapy

AW5

This is a mixture of fluorouracil, thiouracil, heavy metal salts and a steroid. Typically, the treatment involves four to five treatments 48 to 72 hours apart. There is a marked response during treatment (Figure 1) and as such AW5 is highly controlled, only being dispensed for individual horses for specific sarcoids to be applied only by a veterinarian. Used correctly, non-recurrence rates of around 74 percent have been reported (Knottenbelt, 2019). It must not be used near vital structures or where the horse could gain access to the treated sarcoid with its muzzle.

Blood root ointment

This is a twice-daily topical ointment containing Sanguinaria canadensis, a North American plant extract. It is reported to have cytotoxic and immune-modulatory effects. It is relatively inexpensive and one study found 66 percent of sarcoids under 2cm diameter regressed completely (Wilford et al., 2014); it was less effective on previously treated sarcoids.

Fluorouracil (5%) ointment

This has been shown to be effective in treating some super-ficial verrucose or occult sarcoids and it can be used as an adjunctive treatment following surgical treatments (Knottenbelt and Kelly, 2000).

Surgical excision

Conventional excision is risky with high recurrence rates reported. This is likely because the extent of infiltration of the sarcoid into the surrounding tissue is impossible to define. Nevertheless, if the excised tissue is submitted for histopathology the presence of margins can be assessed. The author will usually combine sharp excision with electrochemotherapy (ECT; see later) with further ECT treatments administered if margins are incomplete (Figure 2). A one cut, one blade technique should be used alongside new instruments and re-gloving to close.

FIGURE (3) Diode laser excision of a nodular sarcoid
FIGURE (3) Diode laser excision of a nodular sarcoid

Laser excision

The author uses a diode laser to excise sarcoids where anatomic location allows. The laser vaporises sarcoid cells and generates an area of coagulative necrosis around the margin. This prevents seeding of the operative site during surgery and sterilises the wound bed after excision has been completed. In addition, the thermal injury extends the margin. It can be performed standing with local anaesthesia or under general anaesthesia (Figure 3). A recent study found a non-recurrence rate of 83 percent (Compston et al., 2013) following laser excision. Sarcoids on the head and neck were 1.6 times more likely to recur and verrucose sarcoids were four times more likely to recur. The excision sites are usually left to heal by second intention as they frequently dehisce if primary closure is attempted. Protracted healing can be problematic especially in high motion areas.

Electrochemotherapy

This therapy involves injecting a cytotoxic drug (the author uses cisplatin) into the sarcoid before applying an electric current through the tissue (Figure 4). This increases the permeability of the cell membrane to the drug resulting, in the case of cisplatin, in a four-fold increase in the cytotoxic effects. The resulting necrosis remains localised and the drug only affects cycle cells (by mitotic death), not cells in a quiescence state, such as muscle and nerve cells. The treatments must be performed under general anaesthesia and between one and seven are required, usually three. Nevertheless, the reported 99.5 percent four-year non-recurrence rates (Tamzali et al., 2012) are attractive (Figure 5).

High dose radiation (HDR) brachytherapy

Radiotherapy undoubtedly has very high success rates but the availability and high cost of treatment reduces its use. Recently very high success rates were reported in eight horses with high dose radiation brachytherapy (Hollis and Berlato, 2018); an advantage of this form of radiation therapy is that it can be delivered under sedation. Two doses are delivered one week apart.

Summary

Numerous treatment options are available for this complex skin disorder but careful consideration of the type, location and extent of the sarcoid and funds available will enable selection of the most appropriate treatment for the patient. It is important that owners are warned that any treatment can fail and even make the sarcoid worse. Treatments continue to progress and outcomes are improving; certainly, early treatment improves the chances of resolution.

References
Author Year Title
Compston, P. C., Turner, T. G. and Payne, R. J 2013 Laser surgery as a sole treatment of histologically confirmed equine sarcoids: outcome and risk factors for recurrence. Equine Veterinary Journal, 45, 2
Hollis, A. R. and Berlato, D. 2017 Initial experience with high dose rate brachytherapy of periorbital sarcoids in the horse. Equine Veterinary Education, 30, 444-449
Ireland, J. L., Wylie, C. E., Collins, S. N., Verheyen, K. L. P. and Newton, J. R. 2013 Preventive health care and owner-reported disease prevalence of horses and ponies in Great Britain. Research in Veterinary Science, 95, 418-424
Knottenbelt, D. 2005 A suggested clinical classification for the equine sarcoid. Clinical Techniques in Equine Practice, 4, 278-295
Knottenbelt, D. C. 2019 The equine sarcoid: Why are there so many treatment options? Veterinary Clinics: Equine Practice, 35, 243-262
Knottenbelt, D. C. and Kelly, D. F. 2000 The diagnosis and treatment of periorbital sarcoid in the horse: 445 cases from 1974 to 1999. Veterinary Ophthalmology, 3, 169-191
Tamzali, Y., Borde, L., Rols, M. P., Golzio, M., Lyazrhi, F. and Teissie, J. 2012 Successful treatment of equine sarcoids with cisplatin electrochemotherapy: a retrospective study of 48 cases. Equine Veterinary Journal, 44, 214-220
Wilford, S., Woodward, E. and Dunkel, B. 2014 Owners’ perception of the efficacy of Newmarket bloodroot ointment in treating equine sarcoids. Canadian Veterinary Journal, 55, 683-686

Andy Fiske-Jackson, BVSc, MVetMed, Dipl. ECVS, FHEA, MRCVS, is a senior lecturer, RCVS and European Specialist in Equine Surgery specialising in the use of objective gait analysis in both lameness and back pain cases. He has lectured both nationally and internationally on the subject.

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