Sarcoids can appear in horses of all types, breeds, colours and both sexes. They can develop at any age although most cases are first notice between the ages of 2 and 10 years old. Sarcoids affect horses in all parts of the world and affect around 8% of the UK horse population.

Sarcoids are best regarded as a form of skin cancer. Although some forms are very aggressive the condition is strictly limited to the skin and the tissue directly under it and does not spread to internal organs. They develop most commonly in areas with thin skin, limited or no hair cover and a tendency to sweat. These are also the areas where flies prefer to feed. Sarcoids are rare on the upper trunk, back and neck. At these sites it can be taken as having developed at sites of skin damage. The extent of the damage to the skin may only be slight to encourage development of a sarcoid – for example tack rubs on the face and girth.

Types of Sarcoids

There are 6 different types of sarcoid though not all are easily recognisable. Every type may appear at any site on the body but there are certain predilection sites for each type.

Occult sarcoid

These usually appear as grey hairless circular or roughly circular areas and are often confused with ringworm. Occasionally the only clinical sign may be a subtle change in hair coat colour, thickness and density. This type is most common on the face, armpit, inside thigh and groin areas.

Verrucose sarcoid

These are grey and scaly but tend to extend deeper than the occult sarcoid. They can be small and well defined or cover large, poorly defined areas. They are commonest in the face, groin, sheath and armpit areas.
 
Nodular sarcoid

Discreet solid nodules of variable size which are common under thin and shiny skin occurring commonly around the eyelid and groin. They can be single or multiple. Many have no skin involvement (the skin can be moved freely over the surface) but some are firmly attached to the overlying skin. Occasionally these types of sarcoid can ulcerate and form bleeding exudative masses.

Fibroblastic sarcoid

These sarcoids are fleshy masses either with a thin stalk or with a wide flat base. They may have a wet haemorrhagic surface, are common at almost every site and may develop quickly from a milder form of sarcoid following trauma (however slight). They also commonly develop at the site of skin injuries on the limbs.

Mixed Sarcoid

These are variable mixtures of two or more of the other types of sarcoids. They can develop at any site but are commonest on the head, armpit and groin.

Malevolent sarcoid

This is the most aggressive type of sarcoid but thankfully is very rare in the UK. The tumour spreads extensively through the skin with cords of tumour tissue interspersed with nodules and ulcerating fibroblastic lesions.

Treating sarcoids

It must firstly be remember that sarcoids are difficult to treat. The only thing predictable about sarcoids is their unpredictability. Effective treatment is more likely if lesions are treated early. Treatment for sarcoids depends on the location and type of sarcoid. Homeopathic and natural medicines are entirely unpredictable and usually best avoided. In general cell stimulators such as Allovera and Tea Tree Oil are contraindicated and can be deleterious when applied to sarcoids.

Failure of any treatment method is usually accompanied by the re-appearance of a more aggressive tumour and often in increased numbers. It is therefore important to select the best possible treatment protocol as the first treatment method.

Common Treatments

Surgical removal

Surgery can be effective for very small lesions in safe areas but carries a relatively high failure rate. Special surgical precautions can be taken to reduce (but not eliminate) the risk of recurrence. Nodular lesions in the groin and thigh areas are sometimes amenable to this method provided that the lesions have no skin involvement.

Cryosurgery

This is only effective for lesions with limited size and depth. It is very time consuming and tedious if many lesions are to be treated. There is a high rate of recurrence and to be effective freezing needs to be aggressive. Treatment may also cause extensive damage to surrounding structures and scarring.

Ligation

This involves applying a tight band around the base of the tumour. While this works well for pedunculated sarcoids there is a high risk of leaving some of the tumour cells behind to grow back.

BCG Injection

This method works reasonably well for nodular and fibroblastic lesions around the eyes but is much less effective elsewhere. It should not be used on sarcoids on the limbs – they will often become much worse.

Chemotherapy

Injection of cytotoxic drugs such as cisplatin into the centre of lesions is a useful method of treatment for some types but is restricted to certain types of sarcoid. The material is also very dangerous to the surgeon and special precautions must be taken before use.

Topical cytotoxic therapy

This involves the application of special creams to the affected region. Research carried out at the University of Liverpool shows that creams such as the Leahurst Sarcoid cream work well on selected cases.

Radiation

This is very expensive and unfortunately unavaliable in New Zealand but is nearly 100% effective. Usually it is preserved for small lesions at difficult sites such as around the eyes and over joints.

There is no effective vaccine for sarcoids. Vaccinations make from bits of the sarcoid are unlikely to be of benefit and may make matters worse in many cases. Accidental or intentional (through surgical intervention) damage to a sarcoid may result in a more aggressive lesion with rapid re-growth. Treatment of recurring sarcoids is much more difficult that those lesions that have had no previous interference. Horses do not die from sarcoids but many are euthanased because sarcoids are preventing them from working or enjoying life.

An early diagnosis and with a prompt and effective treatment is the best overall policy. If you suspect your horse has sarcoids do not wait for the condition to get better as it is unlikely to do so. Treatment becomes increasingly difficult with advancing time and clinical deterioration.

For further information click here to view Dr Derek Knottenbelt's website, a leading expert on sarcoids.

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