Types of Equine Sarcoids

There are many different types of equine sarcoids with a range of appearances and behaviors. Different equine sarcoids may need different forms of treatment depending on how aggressive the tumor is. 

Occult Sarcoid 

Occult equine sarcoids represent the earliest form of the disease and can remain stable for many years without causing any problems. They usually appear as a roughly circular and hairless area or as an area that has poor hair quality. They can appear anywhere on the body but are uncommon on the lower legs of the horse. The occult sarcoid is often confused with a rub mark from tack, ringworm or other diseases that result in localized hair loss.

Verrucose

These are slow-growing tumors that have a grey, scaly or wart-like appearance. These are the least aggressive type of sarcoid. Most verrucose equine sarcoids will have an area of hair loss surrounding the wart-like growth, while the growth itself may have a lot of flaking of dandruff-like material. Some verrucose sarcoids develop localized ulceration where the surface cracks open and exposes red fleshy tissue underneath. These sarcoids may appear anywhere on the body, though it is rare to find them on the lower leg. 

Nodular

These are well demarcated lumps that can be covered by normal skin or may be ulcerated. They have a round appearance and may have a wide, flat base or a narrow stem-like base. They have a moderate growth rate but their behavior may change over time. These equine sarcoids are commonly found in the eyelid, armpit, inner thigh and groin area. Nodular sarcoids can vary in size and may be found alone or in clusters that resemble a bunch of grapes. 

Nodular sarcoids come in two types: 

• Type A: where the skin can be moved freely over the surface
• Type B: where the skin is firmly attached to the sarcoid so the skin cannot be moved. 

The A and B types are further divided into sub-groups: 

• Type A1: Nodular Sarcoids have no attachment to the skin or to the surrounding and deep tissues. They can be moved freely and independently over the tissues surrounding it. Surgical treatment or ligation (banding) of these is relatively safe if performed by your veterinarian.  
• Type A2: Nodular Sarcoids have deep attachments to the underlying tissues and therefore, cannot be moved independently of the deep tissues away from deeper tissues. The skin over the nodular sarcoid can however be moved freely. The lack of mobility means that A2 nodular sarcoids can be much deeper and recurrence is very common. Surgery or ligation (banding) will not be successful.
• Type B1: Nodular sarcoids have no deep attachments but are firmly attached to the overlying skin. 
• Type B2: Nodular sarcoids are attached to and infiltrate the surrounding tissue and structures. This sarcoid represents a very serious form of the disease. 

Fibroblastic

Fibroblastic equine sarcoids are fleshy and aggressive in appearance and can be divided into two groups: 

• Type 1: Fibroblastic Sarcoid with a narrow pedicle (a stem attaching the sarcoid to the body)  Type 1 fibroblastic sarcoids can be further divided depending on whether there is extension beyond the pedicle. Differentiation between the types by your veterinarian is essential for proper treatment. 
• Type 1a: Fibroblastic Sarcoids have no root extension beyond the pedicle or stem. Removal of the external mass of a type 1a fibroblastic sarcoid should result in a cure. 
• Type 1b: Fibroblastic Sarcoids have a narrow pedicle or stem but a root that extends into the body beyond the pedicle. Removal of the bulk external mass from a type 1b fibroblastic sarcoid would be a potential disaster!
• Type 2: Fibroblastic Sarcoid with no pedicle are also known as rooted sarcoids. The roots are broad, highly penetrating and can extend far beyond what is visible. Type 2 fibroblastic sarcoids are prone to bleeding, making them attractive to flies. 

Mixed Sarcoids

These are a combination of the above eqine sarcoids. It is fairly common for horses to develop multiple sarcoid types in one region or for there to be multiple sarcoid types at different locations on a horse. 

Malignant Sarcoids

Malignant equine sarcoids have extensive and wider spread through the skin and underlying tissue, but are (thankfully) rare. This is the most aggressive type, with tumors spreading extensively throughout the skin with cords of tumor tissue interspersed with nodules and ulcerating fibroblastic lesions. There are often overlying verrucous and occult tumor changes in the skin accompanying malignant sarcoids.

Affected horses typically have multiple sarcoids at other sites. Large sarcoids are sometimes incorrectly called malignant sarcoids but the term refers to the extent of local infiltration and extension and not the size of the tumors. 

Coming Up Next!

In my next blog, which will hopefully come out in mere days, I will talk about the common and uncommon treatment options available for sarcoids. I will also post some of the images of the sarcoids we are seeing resolve with the feeding of our spirulina chia. (It’s truly exciting and amazing!) Most of the common treatments are covered in the links at the bottom so grab one and read on if you’re keen to add to your knowledge.

REMINDER: If you believe your horse has a sarcoid or you know your horse has a sarcoid and it is causing them discomfort, please contact your veterinarian. I am not an equine veterinary professional so nothing I write should be construed as medical advice. I cannot diagnose your horse or make decisions regarding their care and with some of these sarcoids, you really need to be certain you are following the correct treatment path.