Episode 15 - Knotty ’Nother Sarcoid!

The Skin Flint Podcast

10-01-2023 • 50 mins

Ep.15 Show Notes

In this Skin Flints episode, the team were delighted to host one of the giants of the equine world - the brilliant Derek Knottenbelt (or Knotty, as he is also known).

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Chapter one: Knotty

(03:49) Sue introduces Derek Knottenbelt who gives his background in the industry and his practical emphasis.

(05:09) Sue asks Derek "what is a sarcoid?". He describes it as a reactive skin tumour – so skin cancer is the best way to think about it and not viral as it has been before which has resulting in an incorrect approach; a multi-morphology skin tumour affecting all equid species and continuing to puzzle the scientific world.

(07:00) Sue asks whether it can be contagious given it is a tumour and Derek says that it is his contention that it is transmissible with circumstantial evidence to suggest this, but the mechanism for this is very little understood – it has some relationship with the bovine papilloma virus.

(08:06) Sue asks flies are spreading this and Derek says it is – where sarcoids occur tend to be where the skin is thin – where flies can feed with impunity – where it sweats and there is less hair and therefore where flies feed. Derek doesn’t believe it is the biting fly that transmits it – but a surface feeding fly which feeds on a sarcoid and then transfers the sarcoid element into the site of skin trauma on another horse – which could include where a biting fly had caused tissue damage.

(10:12) Sue says this would fit with periocular sarcoids as flies tend to feed there and Derek again agrees, saying wherever sarcoids occur rarely, they are always associated with wounds which further demonstrates this.

Derek uses the analogy of surface feeding flies being like teenagers going to MacDonalds, where the food is greasy, warm and available at almost no cost – whereas biting flies are like Richard Branson who wouldn’t dream of going to MacDonalds but a 5 star Michelin star restaurant – before then saying sometimes the biting flies go there after and have a pub drink and transfer the sarcoid.

This all fits the epidemiology of the disease – but the process of exactly how this happens and the link to bovine papilloma virus is not yet fully understood.

(12:36) John summarises the conversation so far and Derek goes on to show how in 1985 in a survey 2.5% of British horses had sarcoids, with an average of 2.5 sarcoids each. In 2018 this had risen to 8% of British horses with an average of 24 sarcoids each - so this disease is steadily increasing.

Chapter 2: Sarcoidy

(15:06) John asks if there are any breeds, ages or predispositions which are more susceptible and Derek says that whilst some studies have demonstrated this he does not think it is so simple having seen sarcoids in just about every breed that is available – he says there are genes which impart susceptibility as there have been outbreaks within families of horses. So it is very difficult to isolate. He also studied age of onset within a study of close to 30,000 horses and the numbers merely mimicked the population – so no definitive evidence, and he has seen 40 year old and 17 day old horses with sarcoids. He is more convinced of conditional, situation and environmental factors over any of age, breed, gender and colour.

(19:05) Sue asks about sarcoids themselves – what do they look like? Derek says it is often misdiagnosed as something else because of how multiformal it is. Because it is a tumour of fibroblasts and not epithelial cells often what you see bears no relation to what you would perceive as a fibroblastic tumour. This is because of the effect of the viral component on the disease and the impact this has on the surround tissues.

So firstly the occult form of sarcoid is not the occult tumour – but may contain the tumour – and this must be kept in mind. He goes on to say the circular nature of this form is in effect a result of the mediators diffusing out from the centre. Then the centre begins to develop and become more dermal / epidermal and morphs into something more like a wart, but is not a wart but a ‘vericosal, wart like tumour’, the next from of sarcoid.

Then the next stage/form is either a hard mass-like nodule of fibroblasts called a type A nodule and is completely subcutaneous, or a type B nodule which is attached to the skin dermis. These are easy to identify and are very easily characterised.

Then there is a fleshy form which is very aggressive, vascularised and ulcerated (usually infected) tumour which appears like granulation tissue.

Derek says each of these types has its own potential differential diagnosis which makes them very open to misdiagnosis.

(27:07) Sue asks what causes the transition of one for, to another and if that should point to biopsy. Derek says that with the age of the tumour there is a constant progression, and traumatising the lesion will only accelerate this process (such as with a harness or a buckle, or the movement of the skin in mobile areas). This means biopsy, whilst definitely useful, is only worth doing if you have a plan of what to do when you find it is a sarcoid - as it will otherwise just exacerbate the problem.

Chapter 3: Treatmenty

(30:53) John asks then what the treatments are for a sarcoid and Derek says superficial lesions require less interventions and a 5% or 10% floriorisol and if this does not work a imiquimod – but it is important to bear in mind they are still dangerous because they don’t like being treated, so if you aren’t successful they worsen and a real determination is needed with the disease to keep progressing to the next step. A surgical or laser excision could be considered but it is critical these are sent for pathology for margins to know if you have removed it all – as not doing so require further action.

(35:04) Sue asks what the prognosis is, with good margins and without; Derek says a successful, safe margin of removal is a good base for a start – however there can be tumour cells seeded during surgery and indeed after on the scar from fly attack -so this must still be treated cautiously. If you haven’t got a successful margin you will get deep root recurrence – so by the time you see the tumour it will be twice as big. In this instance Derek likes multimodal therapy, using immunologic methods such as immunosiden, BSG or radiation, or local chemotherapy. Derek goes on to discuss types of localised chemotherapy – also pointing out you can add other therapy such as cryosurgery on top as well. Each time you are adding on a little prognosis – but Derek points out the only thing predictable about a sarcoid is that it is unpredictable and there are over 40 treatments to consider in managing these with new therapies coming out all the time and he lists some of these, but warns against the nonsense brigade – with poor evidence based treatments on the market such as marmite or toothpaste – successes in these instances are coincidental to spontaneous resolution.

(44:55) John wraps up the conversation and summarises, while sue mentions Equine Medical Solutions (Derek’s app).

Outro

(46:58) John brings the podcast to a close by putting Sue and Paul on the spot was another probing question...

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