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