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==Introduction==
[[Image:Pedunculated sarcoid donkey.jpg|right|thumb|200px|<small><center>A large pedunculated (Type 1a, fibroblastic) sarcoid.
This was removed using laser surgery and after three years no recurrence was present.(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
[[Image:Large sarcoid donkey.jpg|right|thumb|200px|<small><center>A large fibroblastic (Type 2, sessile) sarcoid on the medial stifle region that recurred each time following ill-advised attempts to remove it surgically.(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
This is by far the commonest skin tumour of the donkey worldwide and it
has, therefore, been the subject of a considerable research effort centred at
the University of Glasgow in particular, in co-operation with [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary].
A '''virus aetiology''' has been suggested, but the epidemiology in both
horses and donkeys is not fully explained by this possibility. There are clearly
aspects of oncogenic mechanisms that are involved in the condition. There
are families that appear to be particularly susceptible and there is much
anecdotal evidence of ‘contagion’.
There is no doubt that donkeys are severely affected, but the type and
distribution of the sarcoid is somewhat different from that seen in horses.
<u>Donkeys appear to be more liable to severe, invasive and fibroblastic lesions</u>.
Occult and verrucose sarcoids are less often reported, although whether this is because they are not recognised as
easily, or whether they are genuinely less prevalent, is unknown.
==Predilection sites==
Predilection sites for sarcoid in donkeys include the '''face''' (especially around the '''mouth''' and '''eyes''') and
in particular the '''groin''' and '''sheath''' regions.
Any mass around the eye should be considered for sarcoid, as it is a predilection site. It is normally obvious by its appearance and nature.
==Diagnosis==
Notwithstanding the diagnostic benefit that can be derived from biopsy it is probably unwise to
biopsy a sarcoid lesion without a plan for its immediate treatment.
==Treatment==
Prompt action must be taken. Referral should be considered, as the treatment options are limited. Take a photograph and describe precisely if advice is sought.
The treatments available are very limited and all have problems of one sort or another. The reality is that
early treatment of any sarcoid may serve at least to limit the long-term severity, but ill-advised attempts
that lack proper thought may simply exacerbate the problem.
===Surgical excision===
Surgical excision may be an effective option where the limits of the sarcoid can be defined, but simply debriding
the bulk of the lesion or failure to include a wide enough margin may result in a dramatic deterioration.
It is now well established that recurrence at the site of a sarcoid
excision surgery is a common feature and that this can arise either from
partial excision or from seeding of the operative site with cells from the
lesion itself. In D. Knottenbelt’s experience, the latter results in more extensive
exacerbation than the former.
===Cryosurgery===
Cryosurgery is also possible but suffers from the same limitations. The
hitherto recognised ‘remote’ effects on sarcoids at other sites (suggested to
be due to haematogenous cryo-antigens released into the blood) do not occur
in donkeys in D. Knottenbelt’s experience. Cryosurgery is limited in its efficacy
to small lesions in convenient sites and to limited numbers. The simple
application of liquid nitrogen to the skin of any animal without proper
control or the use of thermocouples and uncontrolled freezing with liquid
nitrogen applied directly is totally unacceptable as a veterinary procedure.
===Thermal cautery and 'burning'===
‘Burning’ the lesions with red-hot irons and electrically heated wires are
totally unacceptable – they are illogical, cruel and do nothing to help the
disease. However, there are anecdotal reports of post-excisional thermal
cautery carrying a better prognosis than surgery alone.
===Laser surgery and diathermy===
Laser surgery and diathermy are logical provided that they are carried
out under controlled conditions by experienced surgeons.
===Immunological mechanisms===
Immunological mechanisms may be of value. There are anecdotal
reports of the benefits of '''autologous blood injections''' but it is very hard
to see any immunological benefit from this approach. The reality is that a
'''few cases do seem to resolve spontaneously''' (although this seems to be less
common in donkeys than in horses).
The use of '''intra-lesional BCG''' has been advocated and this appears
to be a useful, but by no means certain, treatment for '''localised nodular
and fibroblastic lesions around the eyes''' of the donkey. The critical factors
appear to be the true intra-lesional injection; peri-lesional injection has no
material benefit and risks the development of anaphylaxis. The mechanism
for the effects of BCG are probably due to its intense chemotactic nature:
macrophages and neutrophils and some mononuclear cells are actively
drawn into the site and remove cells to which the BCG has adhered.
Repeated injections are required and, as the tumour becomes necrotic and
decays, true intra-lesional injection becomes more difficult.
===Cytotoxic compounds===
Topical cytotoxic compounds based on heavy metals and cytotoxic
and antimitotic chemicals, such as '''cisplatin''' and '''5-fluorouracil''', are valuable
because they are convenient and relatively cheap. '''AW4-LUDES''' from
Liverpool University is possibly the best known of these. Often these are
the only material options available. They do, however, cause much tissue
necrosis and '''some pain is inevitable'''. The results suggest that some localised
lesions, and those that have a superficial nature, are more susceptible to
the methods, but again there are wide variations in response and not all
lesions will respond.
===Other materials===
There are many questionable materials that purport to be effective
treatments, but most of these (if not all) have no proven efficacy and have
not been studied properly. For the most part unproven and non-veterinary
treatments should be avoided as far as possible.
The gold standard for treatment of the equine/asinine sarcoid is
radiation but the availably of teletherapy and interstitial brachytherapy is
very limited. The expense and practicality are severely limiting factors.
==References==
* Knottenbelt, D. (2008) Skin disorders In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) ''The Professional Handbook of the Donkey'', 4th edition, Whittet Books, Chapter 8
* Grove, V. (2008) Conditions of the eye In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) ''The Professional Handbook of the Donkey'', 4th edition, Whittet Books, Chapter 11
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