Equine Dermatology Flashcards
Important feature of equine skin
Rich in sweat glands
Are there sweat glands in distal limbs?
No
Length of hair cycle
4-6 weeks
(Slow, hair takes time to grow back)
Hormones driving hair coat shedding
Melatonin and prolactin
Daylight driven
(Short days = increased melatonin and declining prolactin = winter coat)
Most common hypersensitivity type (associated with sweet itch/insect bite hypersensitivity)
Type 1
IgE mediated/histamine release
Hypersensitivity associated with pemphigus foliaceous
Type 2
IgG mediated/cytotoxic response/complement binding
Which hypersensitivity type causes vasculitis and can happen after strangles resolution?
Type 3
Immune complex deposition on endothelial beds –> neutrophil activation –> vasculitis
(Pastern leukocytic vasculitis/purpura haemorrhagica/lupus)
Hypersensitivity type related to insect bites and drug eruptions
Type 4
T cell mediated
Coat brushing is good to look for…
Ectoparasites (sucking louse, biting louse, feather mites)
Diagnostic technique for Oxyrus equi
Acetate tape (on anus)
Culture medium for fungi
Saboureau’s dextrose agar
(PCR more accurate and faster)
Two main categories of disease that cause pruritis in the horse
Ectoparasites
Hypersensitivities
Conditions that have crusting and scalding
Rain scald
Ringworm
Photosensitisation
Pemphigus
Onchocerca
Conditions that present as ulceration and erosions
Viral
Neoplasia
Pressure sores
Summer sores
Pigmentary abnormalities in horses (2)
Vitiligo
Alopecia areata
Should small masses on the horse be removed or watched?
Remove
Should biopsies of masses be incisional or excisional?
Excisional
Colour of horse that most commonly gets melanoma
Grey
Age that melanomas typically first develop
4-8 years
The four types of melanoma
Melanocytic nevi (single or multiple discrete nodules)
Dermal melanoma (originate in deeper dermis, small singular or multiple nodules)
Dermal melanomatosis (confluent large melanomas, increased risk of metastasis)
Malignant melanoma (rare, invasive, older horse, recurrence likely)
Typical locations of melanomas
Tail, perineum, parotid region, commissure of lips/eyes
Diagnosis of a melanoma
Visual inspection
Ultrasound
FNA (black pigmentation on slide)
Likelihood of metastasis of an anaplastic malignant melanoma
Very high, will likely have metastasized at time of diagnosis
Treatment options for melanomas
Cimetidine anti-tumour activity
Oncept (canine DNA vaccine)
Key features of sarcoids
Benign
Non-metastatic
Locally aggressive
High recurrence
Affect all equids
Most common skin tumour in horse
What is a differential for a sarcoid? (Due to similar presentation)
Squamous cell carcinoma
What are the six sarcoid types?
Occult
Verrucose
Nodular
Fibroblastic
Mixed
Malignant
Occult sarcoid features
Most mild, stable and superficial type of sarcoid
Hairless skin
Small (2-5cm) cutaneous nodule(s)
Mild hyperkeratotic region surrounding
Verrucose sarcoid features
Rough hyperkeratotic appearance with flaking/scaling
Warty looking
Rarely aggressive until injured, friction/rubbing triggers change
Nodular sarcoid features
Variable size (0.5-20cm)
Firm, spherical, subcutaneous nodule
Usually not an issue until injured
Type A: subcutaneous tissue only
Type B: involvement of overlying skin
Fibroblastic sarcoid features
Ulcerated and fleshy
(Easily confused with injured nodular sarcoid but has ‘cauliflower appearance’)
Type 1: pedunculated with small base
Type 2: wide base, ill-defined margins
Mixed sarcoid features
Transient state between verrucous/occult/nodular to fibroblastic
(Usually becoming more aggressive)
Malignant/malevolent sarcoid features
Most severe and highly infiltrative (infiltration lymphatic vessels)
Often following trauma/failed treatment (–> chronic wound)
Cord of palpable tumour
What disease can sarcoid-affected horses carry?
Bovine papillomavirus (BPV) type 1 and 2
What transmits bovine papillomavirus between cows/horses (which has links with sarcoids)? What precaution should you take regarding this?
Fly (shouldn’t do sarcoid surgery in summer)
Most locally invasive skin tumour in the horse?
Squamous cell carcinoma
Predilection sites for squamous cell carcinomas?
Areas lacking pigmentation (Appaloosa/Quarter Horse/Paint)
Poorly haired areas
Mucocutaneous junctions
External genitalia
What is the most common neoplasia of the equine eye?
Squamous cell carcinoma
Predisposing factors for squamous cell carcinoma
Equus caballus papillomavirus 2 (EcPV2)
Flies
Smegma around genitalia
UV light
Which sarcoids is ‘banding’ an appropriate treatment method for?
Sarcoids with a thin peduncle (more successful with topical treatment)
Treatment options for sarcoids
Topical cream
Banding
Intralesional chemotherapy (Cisplatin in sesame oil/Mitomycin C)
Surgical excision (laser/sharp)
Electrochemotherapy
Vaccines
Radiotherapy
