VET CLINIC
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Mark Andrews, BVM&S CertEP MRCVS, of
Equine Science Update
we are pleased to provide the latest Equine Veterinary Information
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SARCOIDS.
Sarcoids are the most common skin tumour of the horse. They can occur anywhere on the body, especially on the head around the eyes, lips and ears, on the legs and underneath the body. Sarcoids are often locally very aggressive, and are highly likely to recur if removed. They do not metastasize (spread) and rarely regress spontaneously.
A sarcoid is a locally invasive swelling involving fibroblasts. These are the cells responsible for producing connective tissue.
What do they look like?
Six forms of sarcoid have been recognised:
Occult. This type is found on the head, neck, brisket and groin. They appear as hairless areas of slightly thickened skin, and may contain small nodules. Occult sarcoids usually progress slowly, but if damaged may rapidly develop into one of the more aggressive types.
Verrucous ("warty").These look like warts, with a grey crusty surface. They are most commonly seen on the head, neck and groin. They are usually slow growing until they are damaged. They may be surrounded by a patch of abnormal skin (occult sarcoid)
Nodular. Around the eyes or in the groin are common sites for this type of sarcoid. They appear as a firm nodule underneath the skin. Damage to the overlying skin is likely to cause it to become more aggressive and transform into the fibroblastic form. Sometimes the skin overlying the nodule may split and the nodule may be expelled.
Fibroblastic. This is an aggressive ulcerated mass, that can be confused with granulation tissue. It often appears at the site of previous wounds or results from one of the less aggressive forms of sarcoid being damaged (either accidentally or by surgery).
Mixed. A combination of any of the other types. Eventually they become more aggressive as they change into the fibroblastic type.
Malevolent. This form is rare, but has been reported on the face, inside the thigh and at the elbow. It consists of multiple nodular or fibroblastic sarcoids which invade the lymphatic vessels. It can occur without any previous history of sarcoids, but more commonly results from repeated damage to other forms of sarcoid.
What causes sarcoids?
They are probably caused by a papilloma (wart) virus. A high proportion of sarcoids contain genetic material that is identical, or very closely related, to bovine papilloma virus (BPV). However, no live virus particle has been found. Experimentally, it is possible to produce sarcoid-like swellings by injecting horses with BPV, but usually the swellings resolve spontaneously. So it seems likely that the host response is an important factor.
There appears to be a genetic predisposition. Certain family lines are more susceptible than others to sarcoids. It has been suggested that an autosomal recessive gene controls the degfree of agression shown by the sarcoid.
How do you know it`s a sarcoid?
Usually the clinical appearance is adequate to make a diagnosis. This is especially so if several sarcoids of more than one type are present on the same horse. It is more difficult if only one occult sarcoid is present.
A biopsy (removing a small piece of tissue for examination under the microscope) will usually confirm the diagnosis, but is best avoided, unless it is possible to remove the whole mass. Partial biopsies are likely to induce the fibroblastic form. Furthermore, small biopsies may not include enough tissue features to reach a diagnosis.
The fibroblastic form presents particular problems in diagnosis in that it has a fleshy, ulcerated appearance which may be indistinguishable from exuberant granulation tissue (proud flesh). Sarcoids are even more difficult to identify when they occur at the site of an open wound and are mixed with granulation tissue. If proliferative granulation tissue results from wound breakdown, especially if sarcoids are present elsewhere on the body- it is best to have a biopsy to detect sarcoids early.
So, as a general rule, a biopsy should only be considered if the whole mass can be removed or if there is wound breakdown in the presence of sarcoids.
A new technique developed in Belgium offers the possibility of detecting sarcoid involvement in wounds or sarcoid recurrence after removal. A swab or scraping from the surface of the tissue is examined for the presence of BPV-DNA using a polymerase chain reaction technique, a very sensitive method of detecting genetic material. 1 This technique offers no advantages over clinical appearance for diagnosis of most types of sarcoids. But it is useful in ulcerated lesions to differentiate sarcoid from granulation tissue.
Treatment
Sarcoids are notoriously difficult to treat. The fact that numerous treatments have been described, serves to indicate that there is no single magic cure. Half-hearted attempts at treatment are likely to lead to failure. Ineffective treatment may be worse than doing nothing. It may make the sarcoid more aggressive and turn an occult or verrucous sarcoid into a fibroblastic one.
Experience has shown that certain methods may be more appropriate for each different type or position of sarcoid. No effective treatment is available for the malevolent form.
Ligation. This is effective for smaller sarcoids with an obvious "neck" of normal skin. A length of nylon or elastic is tied around the neck, cutting off the blood supply. Rubber rings used for lamb castration work well.
Surgical excision. This carries a considerable risk of recurrence, except in smaller isolated sarcoids. It is important to make sure that the incision is in healthy skin . This is especially so for occult sarcoids. If the wound can be closed after removing a wide margin of normal skin around the sarcoid it will probably heal satisfactorily. Sarcoids may recur at the site of excision up to several years after removal.
Cryosurgery. This is useful for smaller sarcoids. Liquid nitrogen is used to freeze the sarcoid which then dies and sloughs off. It may be that this provides some stimulus to the immune system - and may cause regression of other sarcoids in some cases.
It is difficult to apply to large lesions and on the eyelids. In larger masses the main bulk of the sarcoid may be cut off ("debulked") first, and the remnant frozen. Usually at least three freeze-thaw cycles are used. Sloughing of the dead tissue may take up to 2 months.
Electrocautery. This technique can be used for removing sarcoids. It reduces bleeding by heating the edge of the wound and so may reduce the risk of recurrence.
Laser (carbon dioxide- YAG) laser . Like electrocautery, it may damage cells beyond the line of the incision and so reduce the risk of recurrence. It also reduces bleeding.
Hyperthermia is not widely used, and requires repeated application.
Chemotherapy. Compounds containing heavy metals such as arsenic, antimony and mercury salts, may be applied to the sarcoid. One example is the cream used by Liverpool vet school which also contains corticosteroids and cytotoxic drugs.
Cisplatin is a cytotoxic drug ( ie it kills cells.) It works well when injected into nodular or small fibroblastic sarcoids. One small study found it to be 100% effective.
Immunological
Autogenous Vaccine. Some people have advocated using sarcoids removed from the horse to produce a vaccine which is then injected back into the horse to stimulate resistance to the remaining sarcoids. Vaccines do not usually work well. In some cases the remaining sarcoids get worse after autogenous vaccine treatment.
BCG vaccine. This was originally produced to protect people against tuberculosis. It is injected into the sarcoid on 3 or 4 occasions at 2-3 week intervals. It acts as an immune stimulant and works quite well for some nodular sarcoids and some fibroblastic sarcoids. Sarcoids around the eye seem to respond well to this treatment.
Radioactive Gold and Iridium implants. These have been used successfully especially around the eyes. But requirements for radiological protection of the operator make it an impractical treatment in most cases.
Should I buy a horse with sarcoids?
There are several things to consider:
Remember that sarcoids are unpredictable. A solitary sarcoid may remain unchanged for the life ogf the horse. On the other hand, it may suddenly become aggressive.
If the sarcoids are in an area where the tack will damage them then it is very likely that they will cause a problem in the future. If treatment becomes necessary, it may be expensive and may not be successful.
Insurance companies will not cover treatment for sarcoids that were presentwhen the insurance started. So, if the horse does need treating you would have to pay yourself.
Although you may be happy to live with a horse with sarcoids, a prospective purchaser may not. Later, if you want to sell the horse, it is likely that the sarcoid will have progressed and so you may have difficulty selling it. The eventual price obtained may be less than you would otherwise have expected.
References
1. http://www.equinescienceupdate.co.uk/sarcoid.htm
2. see also:http://www.pcweb.liv.ac.uk/sarcoids/Index.ssi (Information on sarcoids from Liverpool Vet School.)
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