Sarcoids Come in Many Types

There are 4 main types of sarcoid:

Occult ; Verrucose ; Nodular ; Fibroblastic

Each has a different appearance and what you see on the surface may just be the tip of an iceberg with roots of the sarcoid growing down into the deeper tissues.

Vets are trained to recognise the different types of sarcoid. Each type may require a different treatment approach.

Horses may have more than one type of sarcoid at any time and may have more than one type in any one area (Mixed Sarcoid).

mixed verrucose and nodular
Type B2 nodules
Sessile fibroblastic IMG_8020

Occult Sarcoid

Occult sarcoid represent the earliest form of the disease.

Some of occult sarcoids remain stable for years without any problem.

Occult sarcoids can occupy large areas, or be very small and subtle.

Occult sarcoids usually appear as a roughly circular hairless area, or an area that has altered hair quality.

Sometimes the only change may be subtle changes in the hair coat colour, thickness and density.

Later forms of occult sarcoid usually appear as grey hairless,  circular areas. There may be one or several tiny nodules in the skin which can be felt in the area.

The skin may feel  thickened and lacks its normal elasticity.

Occult sarcoids can occur at any body site but are rare on the lower leg region.

They can easily be confused with rub marks from tack or rugs, as well as many skin conditions such as: Ringworm, Alopecia Areata, Pemphigus Foliaeceus and Dermal or epidermal Naevus.

Verrucose Sarcoid

Verrucous sarcoids usually have a grey, scaly or warty appearance. This is why some people used to call them equine warts (which is inapproriate given that they are actually a type of skin cancer!)

Verrucous sarcoids can be small wart or papilloma-like extensions from skin

Verrucous sarcoids frequently coalesce into larger lesions and affect large areas.

Most early verrucous sarcoids have an “occult halo”. This is an area of hair loss (alopecia)  or hair thinning around the sarcoid.

Sometimes small solid nodules that feel like a pea under the skin can be felt within the verrucous sarcoid. The skin also lacks normal flexibility and may crack easily.

Most verrucous sarcoids are scaly with a lot of flaking and dandruff like material. Flakes and scale can easily be rubbed from the surface. Others are simply scaly in texture.

Some verrucous sracoids can develop localised ulceration, where the surface comes away exposing red, fleshy tissue underneath.

Verrucous sarcoids can occur anywhere on the body. However verrucous sarcoids on the lower leg, especially around the coronary band are rare.  Verrucous sarcoids can be mistaken for many other conditions such as: Ringworm, Alopecia Areata, Pemphingus Foliaceus, excessive scar formation (cheloids) at a wound site, or overgrowth of skin as a result of repeated trauma or rubbing.

Nodular Sarcoid

Nodular sarcoids are are much easier to see and identify. They are discrete, firm, defined nodules under the skin.

Nodular sarcoids are commonly located  in the eyelid, armpit (axilla), inner thigh and groin

Nodular sarcoids vary in size and be single nodules of multiple nodules and can sometimes give the appearance of a bunch of grapes.

Nodular sarcoids can ulcerate resulting in bleeding masses which attract flies

Nodular sarcoids come in 2 types:

Type A where the skin can be moved freely over the surface

Type B which are firmly attached to the overlying skin, and the skin cannot be moved over the surface.

Type B nodular sarcoids can develop from type A nodules, especially if the nodule is interfered with. They can also develop spontaneously over time.

They are further dividied into types A1, A2, B1 and B2

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 veterinary surgeon. Never attempt to band one yourself!

Type A2 Nodular Sarcoids have  deep attachments to the underlying tissues and therefore,  cannot be moved independently of the deep tissues away form 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.

In Type B nodular sarcoids the overlying skin may be hairless (alopecic) and scaly (verrucous).

Some Type B nodules ulcerate over to expose a fleshy bleeding surface. This progression can be very rapid. Once nodular sarcoids ulcerate they often rapidly develop into fibroblastic or malignant sarcoids.

Type B nodular sarcoids have poorly defined margins. This is why they feel fixed.

Eyelid nodular sarcoids of this type are particularly dangerous.

They develop deep and extensive ‘roots’ that invade between the muscles of the eyelids.

Eyelid tumours are therefore potentially VERY dangerous and should NEVER be interfered with. Professional help must be sought as soon as you have ANY suspicion of change in that area.

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 tissues and structures. The sarcoid has a bound-down feel to it. This represents a very serious form of the disease.

Fibroblastic Sarcoid

Fibroblastic Sarcoid

Fibroblastic sarcoids are fleshy and aggressive in appearance.

They can be divided in to two groups:

Type 1 Fibroblastic Sarcoid with a narrow pedicle (a stem attaching the sarcoid to the body)

Type 2 Fibroblastic Sarcoid with no pedicle

Type 1 Fibroblastic Sarcoids can be further divided depending on whether there is extension beyond the pedicle.

Type 1a Fibroblastic sarcoids have no root extension beyond the pedicle or stem

Type 1b Fibroblastic sarcoids have a narrow pedicle or stem but a root or foot extends into the body beyond the pedicle.

This differentiation is essential for deciding on the best treatment option.

Removal of the external mass of a type 1a fibroblastic sarcoid should  result in a cure, but removal of the bulk external mass from a type 1b fibroblastic sarcoid would be a potential disaster!


Type 2 Fibroblastic sarcoids are also known as sessile or rooted sarcoids.

Type 2 fibroblastic sarcoid is a very serious form of the disease and treatment is always problematic. The roots are very broad, highly penetrating and can extend far beyond what is visible. Type 2 Fibroblastic sarcoids are also prone to bleeding easily. This makes them particularly attractive to flies causing further ulceration and infection.

Fibroblastic sarcoids are common at all sites and may rapidly develop from a milder form of sarcoid following damage. They commonly develop at the site of skin injuries on the limbs.


Treating Fibroblastic Sarcoids early is critical to get the sarcoid more manageable and less ulcerated before the fly season starts. These sarcoids can mean more risk of spread between horses or spread to other sites on the same horse as the flies feed at the sarcoid and move to other areas with a risk of sarcoid development.

mixed verrucose and nodular

Mixed Sarcoid

Many sarcoids are actually a mixtures of types. Mixed sarcoid is a common diagnosis.

As treatment varies so widely between the different types the main type should be identified if at all possible.

Sometimes it is impossible to identify the main type. This includes variable mixtures of two or more of the other types.

Mixed sarcoids are common in long standing lesions or where there has been repeated minor trauma (e.g. tack or harness rubbing) or when inappropriate treatments have been attempted.


Malignant Sarcoid

Malignant sarcoids have extensive local or wider spread through the skin and the underlying tissues. Malignant sarcoids are thankfully rare.

Malignant sarcoids are the most aggressive type. The tumours spread extensively through the skin with cords of tumour tissue interspersed with nodules and ulcerating fibroblastic lesions.

There is often some overlying verrucous and occult changes in the skin.

The skin may remain intact and  there may be no superficial ulceration, especially in the elbow  and flank fold regions.

Affected horses usually have multiple sarcoids at other sites but isolated malignant sarcoids can develop, particularly at the point of the elbow, the medial thigh and the side of the face.

Spread to internal organs has never been recorded with sarcoid and so the term “Malevolent Sarcoid” was used to try to differentiate it from the metastatic tumour (spreading tumours or cancers)  usually thought of as ‘malignant’.

Large sarcoids of other types are sometimes incorrectly called malignant sarcoids. The term refers to the extent of local infiltration and extension NOT the size of the sarcoid itself.

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