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Flashcards in DR: Equine skin disease Deck (49)
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3 commonest cutaneous neoplasms

* sarcoids *
- SCCs
- melanomas


Describe the nature of sarcoids

locally invasive, non-metastatic, fibroblastic, rarely regress spontaneously


Location - sarcoids

- any body part
- singly or clusters
- ventral abdomen, limbs, head, eyes, pinnae, lip commissures
- areas that have experienced trauma


Aetiology - sarcoids

- not definitively established
- ample evidence supports viral agent (high recurrence after complete excision as surgical trauma may induce proliferation and expression of latent virus --> tumour regrowth), flies, shared grooming equipment etc are possible transmission routes


Is susceptibility to sarcoids heritable?



Presentation - sarcoids

- linear or focal dermal thickening
- epidermis: varies, thick, rough and hyperkeratotic to ulcerated
- can occur in subcut tissue: firm, moveable masses, intact skin covering


What are the 6 distinct forms of sarcoids (this classification is not strictly histopathological)

- occult
- verrucous (warty)
- nodular
(- above forms can quickly progress to more aggressive forms, especially if the area is traumatised)
- fibroblastic
- mixed
- malevoelent


Ddx for sarcoid suspicion

- dermatophytosis
- linear hyperkeratosis
- blisters
- burns
- rub marks
- papillomas
- hyperkeratosis
- fibromas
- neurofibromas
- equine eosinophilic granulomas
- melanoma
- pythiosis (infectious fungal disease)
- fibrosarcoma
- lymphosarcoma


Why is biopsy of occult/ nodular/ small verrucous tumours not recommended?

to avoid altering the morphology and behaviour of the lesion - definitive diagnosis based on histologica exam. punch biopsies not recommended


Tx - sarcoids

- wide range
- nothing universally effective
- selected on location, size, aggressiveness, clinical experience, client commitment, services, equipment, facilities
- surgical excision (50-64% recurrence, most within 6 months)
- intralesional implants containing chemotherapeutic agents allow high local drug concentration for extended periods (high molecular weight collagen matrix contains chemo agent and vasoactive modifier: tumours are injected 3-5 times at 2-3 week intervals
- Immiquimod (Aidara) stimulates WBCs
- intratumoral hyperthermia induced by orthovoltage
- cryotherapy with liquid nitrogen (cost effective in many cases)
- Eqstim - non-viable Propionibacterium acnes
- topical treatments
- various radioisotopes
- Immunotherapy - common, BCG most common immunomodulator
- autogenos vaccines


What is the 2nd commonest equine tumour?

SCC (20% of equine neoplasms). It is the most commonly diagnosed neoplasm of eye, conjunctiva, ocular adnex structures, external genitalia and others


How often do SCC metastasise? Where to?

19% cases - local LNs most commonly. Also lungs


What signalment is predisposed to SCC?

- older holders
- draft breeds, appaloosas, american paints and pintos
- stallions, geldings (smegma, persistent phimosis, repeated trauma)


Early CS of SCC

- thickening and mild exfoliation and ulceration


Mature SCC lesions

erosive or productive in nature


Ddx for SCC 4

sarcoids, melanoma, exuberant GT, pythiosis


Dx - SCC

- cytology and histology
- depending on size and site of lesion (excisional, wedge, punch or elliptical biopsy)
- others - FNA (noduar lesions), cytology (superficial scrapings) and impression smears


Tx - SCC

- most successful if initiated early
- debulking + cryosurgery
- intratumoral hyperthermia
- cisplatin
- tpical tx of superficial ulcerative SCC (5-FU) drops and creams
- radiation therapy
- beta irradiation (strontium-90)
- course-fractionated cobalt 60 radiotherapy
- bloodroot extracts


How often does SCC recur after treatment?



Signalment - equine melanomas

- any
- greater incidence in gray and white horses (when they occur in horses of other colours, they may be at greater risk of becoming malignant)
- arabians, thoroughbreds and percherons
- incidence, size and number of melanomas significantly correlates with age (67% prevalence at ages > 15 years)
- no gender predilection


What areas are most commonly affected by equine melanomas?

underneath the tail and the external genitalia. other regions too but less commobnly


Aetiology - equine melanomas

not clearly defined
- old gray horses: due to disturbed melanin metabolism --> formation of new melanoblasts OR increased activity in resident melanoblasts --> focal area of overproduction of pigment in dermis.
- UV light exposure (controversial - frequent exposure in shaded body regions)


How often do melanomas metastasise?

Infrequently - 95% melanomas are slow growing an show no signs of regional or distant metastasis.


Clinical significance - equine melanomas

of little clinical significance except when they inhibit use of riding tack or interfere with urination/defaecation/ coitus etc.


Appearance - melanomas

black or gray, solitary, discrete, firm, spherical or flat nodules in skin or subcutis, may have a pedicle. frequently coalesce, many together produce a cobblestone appearance. overlying skin may be intact or slightly alopecic


Outline melanoma metastatic transformation

occassionally melanomas exhibit slow growth for several years followed by sudden rapid growth associated with malignant trasnformation of tumour, become locally invasive and metastasise. rare instances rapidly grow and are malignant from onset.


Dx - equine melanomas

- generally based on gross appearance
- confirmed with histology ( mostly melanocytes and melanophages)


Tx - equine melanomas - 5

- often not necessary for small melanocytic tumours located in uncompromising locations
- large masses or those in nuisance areas - surgical excision (wide margin)
- cryosurgery can be used in conjunction with excision
- intralesional injection or implantation of cisplatin (effective if tumour <3cm diameter)
- cimetidine (histamine-R agonist. overall enhances immune function and targeting of tumours), regression should be noted within 3 months if not discontinue, monitor liver enzymes


List equine skin neoplasms

- sarcoids
- melanomas
- papilloma
- lymphosarcoma
- rare mesenchymal neoplasms occasionally seen in skin include fibromas, basal cell tumours, lipomas and haemangiomas


What clinical features may be helpful in diagnosing a skin neoplasm?

- failure to respond to appropriate rational therapy