Equine dermatology 2 Flashcards
Neoplasia
Describe melanocytomas
- Rare
- Benign, no coat colour predilection, surgical excision is curative
- Usually young horses
What are eosinophilic granulomas in horses?
Nodular lesions commonly in saddle area, aka collagen necrosis (not histopathologically accurate)
What is the cause of eosinophilic granulomas?
- Precise cause and pathogenesis unknown
- Often occur spring and summer, so attributed to fly hypersensitivity or atopic dermatitis
- Others suggest trauma
Where do squamous cell carcinomas commonly occur?
- Face
- Eyelids/cornea/globe
- Genitalia
- Typically mucocutaneous junctions (but can be anywhere)
What are the risk factors for the development of squamous cell carcinomas?
- Susceptibility to UV light
- Smegma
Describe the spread of squamous cell carcinomas
- Can be along lymphatic chains
- Or by direct transplantation
List the treatment options for melanomas
- Benign neglect/monitoring
- Cimetidine
- Surgical removal
- Intra-lesional treatments e.g. cisplatin, mitomycin C
- Vaccines/immunotherapy
Discuss the benign neglect approach to melanomas
Standard approach, but all lesions will progres
Discuss the use of cimetidine in the treatment of melanomas
- Evidence contradictory
- Oral antacid
- Expensive, off license and need to use for some months
Discuss the use of vaccines/immunotherapy in the treatment of melanoma
- Expensive (approx £2000 for initial course, then £500/vaccine thereafter)
- Unproven efficacy
Outline the treatment of eosinophilic granuloma
- Intra- or peri-lesional steroids (methylpred or triamcinolone)
- Systemic steroids (pred or dex)
- Foam pads may be useful under saddle
- Removal difficult due to tight skin, margins difficult to achieve
List the treatment options for squamous cell carcinoma in horses
- Depends on location
- Surgical excision
- Brachytherapy
- Chemotherapy
- NSAIDs
Where would surgical excision of a squamous cell carcinoma be appropriate?
- Third eyelid
- Penile reeding/distal phallectomy
- En bloc penile resection
Outline the use of brachytherapy in the treatment of squamous cell carcinoma
- Iridium-12 very effective for periocular lesions
- Plesiotherapy (strontium-90 beta-emitter) useful for small lesions and corneal lesions
- Both only available at AHT and expensive
Outline the use of chemotherapy in the treatment of squamous cell carcinoma
- Cisplatin, 5-FU can be effective
- Mitomycin-C shown to be effective topically and intra-lesionally, often used in conjunction with surgical removal
List the treatment options for sarcoids
- Surgical removal
- Ligation
- Cryosurgery
- Immunotherapy
- Chemotherapy
- Photodynamic therapy
- Topical cytotoxic therapy
- Radiotherapy
- Imiquimod, acyclovir, bloodroot ointment, bleomycin, topical mitomycin C, taxarotene
Compare sharp and laser excision for the removal of equine sarcoids
- Sharp: smaller sarcoids e.g. nodular, but failure rate high
- Laser: higher success rate, not widely available, time to heal, looks ugly during but good once healed
Discuss the use of ligation in the treatment of equine sarcoids
- Some owners use hair tails, poor idea
- Only where can be sure there is no root
- Elastrator rings useful for some nodular and pedunculated fibroblastic sarcoids for debulking prior to treatment of source
Evaluate the use of cryosurgery in the treatment of equine sarcoids
- Only for small superficial tumours
- Time consuming
- High recurrence if not used effectively
Evaluate the use of immunotherapy in the treatment of equine sarcoids
- BCG injection for peri-ocular or fibroblastic lesions
- Not for verrucose or occult lesions
- Injected into lesions
- Care re. anaphylaxis
- Not available in UK
Discuss the use of chemotherapy in the treatment of equine sarcoids
- Intralesion injection of cytotoxic drugs e.g. cisplatin, mitomycin C, 5-fluoro uracil
- Can beeffective but danger to surgeon, not recommended
- Topical 5-FU canbe effective
- Requires heavy sedation of horse, draw up in fume cupboard etc.
How does photodynamic therapy work in the treatment of equine sarcoids?
Application of chemical to lesion leads to significant cell damage when exposed to a certain wavelength of light
Evaluate the use of photodynamic therapy in the treatment of equine sarcoids
- Poor penetration
- Only applicable to very small, superficial lesions
- Side effects when animal exposed to sunlight
What is the main topical cytotoxic therapy used in the treatment of equine sarcoids?
- AW5-LUDES (aka Liverpool cream), contains 5FU and other heavy metals
Evaluate the use of Liverpool cream in the treatment of equine sarcoids
- Reasonably effective in certain circumstances
- Requires repeated topical application by vet only, q48-72hours
- Health and safety concerns: nasty, cytotoxic, vaseline on normal skin to protect, gloves
Discuss the use of radiotherapy in the treatment of equine sarcoids
- Treatment only takes a few minutes
- Excellent cosmesis and 95% success
- Expensive
- For periocular lesions, only AHT
- Early treatment for best results
- May result in discolouration/scarring
- NO longer available in UK
Describe the method for radiotherapy treatment of equine sarcoids
- High dose brachytherapy
- high activity Iridium 192 source, emits gamma radiation
- Catheters implanted into lesion, source driven through catheters by remove afterloader
- Treatment takes a few minutes, delivered in 2 fractions a week apart
- Horse not radioactive between treatments
- No operator exposure
List the common causes of crusting and scaling in horses
- Infectious
- Dermatosis of lower limb
- Photo dermatitis
- Seborrhoea
- Localised keratinisation defects
- Immune mediated causes
- Idiopathic causes
What are the main infectious causes of crusting and scaling in horses?
- Dermatophilosis
- Dermatophytosis
- Staphylococcus spp.
Name the dermatoses of the lower limb that lead to crusting and scaling
- Leukocytoclastic vasculitis
- Pastern dermatitis
Name the localised keratinisation defects that cause crusting and scaling in horses
- Cannon keratosis
- Linear keratosis
Name the immune mediated causes of crusting and scaling in horses
- Pemphigus foliaceous (rare)
- Coronary band dystrophy (rare)
Name the idiopathic causes of crusting and scaling in horses
- Multisystemic eosinophili epitheliotrophic disease (MEED) (rare)
- Generalised granulomatous disease (sarcoidosis) (uncommon)
What conditions may allow Dermatophilosis to occur?
- Skin damage e.g. other skin disease, insect bites, environmental trauma
- Wet skin e.g. sweat, rain, washing
Which horses are at risk of dermatophilosis?
- Genetic susceptibility, some more prone
- Immunocompromised/malnourished animals
- Short lived immunity, recurrent infection likely
- Animals in contact withother infected animals (contagious)
Describe the clinical signs of dermatophilosis
- Follicular/non-follicular tufted papules, rapidly coalesce and become exudative, matted hair = paintbrush lesions
- Plucking leaves erosions/ulcerations +/- bleeding, purulent
- Commonly seen on rump and top line, saddle area, pastern, coronet, heels
- Lesions may be painful e.g. distal limb swelling, oedema, lameness
- Rarely pruritic
- Healing produces dry crusts, scaling, alopecia
Outline the methods for diagnosis of dermatophilosis
- History
- Clinical signs
- Impression smears of purulent material and cytology (G+ve branching, filamentous chain like coccus)
- Culture
- Skin biopsy
List the differential diagnoses for dermatophilus
- Staphylococcal folliculitis
- Dermatophytosis
- Pemphigus foliaceous (rare)
- Photo dermatitis (sunburn)
- Other causes of pastern dermatitis
Describe the management of dermatophilosis
- Prevent wetting
- Remove rugs to prevent sweating
- Keep tak and groowing kit clean and for individual
- Most will spontaneously regress in 1 month
- Remove and dispose of crusts carefully
- Topical or systemic treatment may be required
Describe the topical treatment of dermatophilosis
- Chlorhexidine shampoos
- Silver sulphadiazine (flammazine) cream
- Not steroids as is an infection and need immune response to clear
Describe the systemic treatment of dermatophilosis
- Only if horse is systemically ill or chronically infected, not usually the case
- antibiotics e.g. penicillin/TMPS
Describe the epidemiology of cutaneous Staphylococcus infection in horses
- Sporadic infection
- Common spring and summer, post-clipping/during coat change
- Fine skinned horses e.g. TB
- Potentially contagious if shared tack
Describe the clinical signs of cutaneous Staph. aureus infection in horses
- Lesion starts as focal papul
- Hairs stik up against lie of coat, can be glued by small crusts
- Can progress to furunculosis - nodules, draining tracts, ulcers, crusts
- Can get cellulitis, lymphatic engorgement
- Painful - removal of scabs painful
- Lesions mainly on contact areas of tack, saddle pads, rider’s legs
Outline the diagnosis of cutaneous Staphylococcus infection in horses
- Clinical signs
- Swab and culture exudate
- Staph aureus is a commensal, need pure growth for diagnosis
List the differentials for cutaneous Staphylococcus infection
- Pemphigus foliaceous
- Other bacterial infection (Strep/Dermatophilosis)
- Onchocerciasis
Describe the management of cutaneous Staphylococcal infection in horses
- NSAIDs for pain
- Avoid contact with tack, rider, rugs, other horses
- topical antiseptic shampoos - chlorhexidine/povidone iodine based
- Systemic antibiotics
Describe the epidemiology of dermatophytosis
- Highly contagious, potentially zoonotic
- Transmission via contact with infected animals or environment/fomites
- Incubation period 1-6 weeks
- Young animals especially susceptible
- Some immunity with age/post infection
- Endemic in many liver/racing yards
Name the agents that cause dermatophytosis in horses
- Trichophyton equinum and verrucosum
- Microsporum gypseum and equinum
What are the regulations regarding dermatophytosis in race horses
- Not allowed on racecourse with active lesions
- If have old lesions, need form from vet to show they have been treated for dermatophytosis and that infection no longer active
- May also not be exported with active lesions
Describe the clinical signs of dermatophytosis
- Tack contact sites common
- Multiple lesions
- Initially change in angels of hairs
- Small, often circular patches
- Amongst hairs, finely keratinised squames (cigarette ash appearance)
- Hairs easily broken/epilated
- focal areas coalesce leading to extensive scaling and flaking
- Variable pain
- Variable pruritus
How do dermatophyte fungi produce the lesions seen in dermatophytosis?
Produce keratolytic enzymes which lead to weakening of hairs which easily break/are epilated
Describe the healing of dermatophyte lesions and explain the importance of this for sampling
- Healing occurs from the centre
- Hair will usually grow back, but may have some change in colour
- Most active fungal growth is at the margins of the lesion
Describe the methods in the diagnosis of dermatophytosis
- Hair plucks at periphery of lesions for microscopy and culture
- Wood’s lamp not useful in horses
- Skin punch biopsy - fungal spores within hair follicles may be seen
Briefly outline the culture method for dermatophytosis
- Use Sabouraud’s method
- Red phenol dye used, agar red if +ve
- Add drop of vit B to culture to facilitate growth of Microsporum spp.
- Culture can take up to 30 days
Describe the management of equine dermatophytosis
- ID of species not important for treatment
- Most are self-limiting in 5-10 weeks
- Wear gloves
- Main principles: treat active infection to decrease spore formation, and eliminate infective spores from environment
- Usually topical, rarely systemic
- Use disinfectants with anti-fungal action
Discuss the potential causes of pastern dermatitis
- Common, often winter, multifactorial, chronic wetting of skin, white legs predisposed, folds on sire legs
- Infectious: bacteria, fungus, virus, parasite
- Non-infectious: trauma, immune mediated, neoplastic
List the differentials for pastern dermatitis (and briefly state how they differ)
- Dermatophylosis: cursts on top of pus, little pain
- Staphylococcal dermatitis: extremely painful
- Pastern and cannon leukocytoclastic vasculitis: immmune mediated, not painful
- Other autoimmune disease e.g. SLE, immune mediated necrotising vasculitis
Describe the clinical signs of pastern dermatitis
- Mild: alopecia, erythema, mild serum exudation
- Progression to: papules, significant serum exudation, crusts, scabs
- +/- pain on palpation, lameness, cellulitis
Outline the methods for the diagnosis of pastern dermatitis
- Clinical signs
- Coat brushings
- Skin scrapes
- Swabs from exudate (culture/sensitivity)
- Skin biopsy
- Elimination of other causes
Evaluate the use of skin biopsy in the diagnosis of pastern dermatitis
- Often poor return
- May help in recurrent or refractory cases
- Cn be difficult to take from medial/lateral side of leg as blood vessels and nerves shallow under skin
Discuss the key considerations in the treatment of pastern dermatitis
- Owners often tried own methods before call vet
- No single treatment works
- In some cases, not totally resolvable
- Secondary infections with bacteria/fungi lead to complications
Outline a general treatment approach to pastern dermatitis
1: Clean and clip area
2: Debride crusts using cream and bandage overnight to allow topical treatment to penetrate into region where organism is located
3: Next day gently wash with dilute chlorhexidine, dry and clip more if needed
4: Repeat 2 if crusts still present
5: care of balance of over-wetting and need to wash area
6: Apply topical treatment once crusts removed
7: Carefully dispose of crusts and do not reuse same towel to dry
List the topical treatments that can be used for the treatment of pastern dermatitis
- Chlorhexidine
- Antiseptic, antifungal e.g. malaseb
- Antibiotic cream e.g. Flammazine
- Combined antibiotic + steroid cream e.g. fuciderm
What is a key consideration with the use of topical treatment in the treatment of pastern dermatitis?
Care with repeated use of topical steroids as these could delay epithelialisation/cause thinning of skin, but may help with pain/inflammation
Other than creams, what other treatment would be appropriate in the treatment of pastern dermatitis?
NSAIDs in lame horse e.g. phenylbutazone, meloxicam, flunixin meglumine
Outline how pastern dermatitis can be prevented
- Avoid over wetting skin by using barrier creams for exercise e.g. petroleum jelly
- Do not aggressively wash and scrub area
- Clean, dry bedding, avoid prickly straw
- Dry paddocks
What is the cause of pastern leukocytoclastic vasculitis?
Unknown, associated with bacterial infection
Describe the clinical signs of pastern leukocytoclastic vasculitis
- in almost all cases white limbs affected
- Often follows blood vessels on lateral and medial limb
- Firmly attached crusts on distal limbs
How is pastern leukocytoclasic vasculitis diagnosed?
- Skin biopsy
- Will see vasculitis and karryorrhexis of neutrophils
Describe the treatment of pastern leukocytoclastic vasculitis
- Topical steroids
- Systemic steroids e.g. prednisolone/dexamethasone
- Avoid sun
Which areas are predisposed to photodermatitis and how can this be prevented?
- Unpigmented, pink skin e.g. palomino, cream horses
- Areas maximally exposed to sun: nose, muzzle
- Prevented by using suncream
Describe the appearance of photo dermatitis
- Erythema
- Scaling
- Necrosis
How does photosensitisation occur?
- Normal light exposure
- Indirectly caused by photodynamic agents in skin due to ingestion of plants containing photodynamic agents, or failure of liver to detoxify phylloerythrin of hepatotoxic plants
Give examples of plants that can lead to photosensitisation and state which mechanism this is by
- St Johns Wort (Hypericum perforatum): direct absorption of photodynamic agents into blood
- Ragwort (Senecio jacobea): failure of liver detoxicifation
Outline how photosensitisation by plants can be avoided
- Check paddocks and identify plants, remove
- Check and remove from hay (palatable when cut)
Describe the onset of clinical signs of photosensitisation
- Typically not seen until months after ingestion
- Can affect multiple horses in a group
- Not all horses have liver failure, but need to rule this out
Describe the clinical signs of photosensitisation
- Erythema
- Oedema
- Pain
- Vesicles
- Serum exudation
- Skin necrosis
- Ulceration
- Sloughing
- Possible other signs of liver disease
- Secondary bacterial infection
Outline the management of photosensitisation
- Sun avoidance (stable in day, turn out at night)
- UV mask, high factor sun screens, avoid grazing with toxic pants
- Use topical creams to remove crusts and sooth e.g. dermisol, aloe vera
- Evidence of severe liver disease have guarded prognosis (need to check liver parameters in any case of suspected photosensitisation)
Describe the clinical signs of pemphigus foliaceous in the horse
- Lesions start on face, become generalised over several months
- Early lesions papules and crusts
- Annular thick crusts, annular erosions with/without epidermal collarettes, annular alopecia, oozing, matted hair coat, scaling
Describe the diagnosis of pemphigus foliaceous in the horse
- Skin biopsy (acantholysis, neutrophils, eosinophils seen)
- Direct smear of pustule/erosions for cytology
- Immunohistochemistry
Outline the treatment of pemphigus foliaceous in the horse
- Rarely may have spontanous resolutin (foals)
- Aggressive treatment usually with immunosuppressive doses of steroids
- Immunomodulators (azathioprine)
- Gold salts
- Approx 50% r=of cases relapse after prolonged treatment
Describe steroid use in the treatment of pemphigus foliaceous
- Immunosuppressive doses e.g. pred PO SID starting 2-4mg/kg or dex
- Laminitis risk high
What is leukotrichia?
White hair growth on areas of scarring, may be a result of ulcers and erosions
List common causes of ulcers and erosions in horses
- Saddle/tack sores
- Chemical irritants
- Vasculitis
- Chemical/thermal burns
- Coital exanthema (EHV-3)
- Pemphigus vlgaris/bullous pemphigoid
- Inherited defects
- Ulcerative lymphangitis
- Glanders and Farcy
- Epizootic lymphangitis
- Vesicular stomatitis
Identify the notifiable causes of erosions and ulcers in horses
- Glanders and Farcy (Burkholderia mallei)
- Epixzootic lymphangitis (Histoplasma farciminosum)
- Vesicular stomatitis
What are the inherited defects of horses that may lead to ulcers and erosions?
- Cutaneous asthenia
- Epidermolysis bullosa
- Aplasia cutis
What is the causative agent of ulcerative lymphangitis?
Corynebacterium paratuberculosis
What may cause vasculitis in horses leading to ulcers and erosions?
- Post infection e.g. Streptococcus equi equi (strangles)
- Drug related reaction
- Photoactivated
- Type III and type I hypersensitivity
Describe the appearance and treatment of post infection vasculitis as a result of Streptococcus equi equi
- Purpura haemorrhagica
- Urticaria
- Oedema of head, limbs
- Petechiation of mucous membrane
- Exudation
- Skin sloughing
- Treatment: steroids, antibiotics, nursing
List the types of haircoat disorders that may occur in horses
- Hirsuitism
- Seasonal abnormal shedding
- Anagen deluxation
- Telogen defluxation
- Coat colour changes
- Alopecia
Briefly describe seasonal abnormal shedding
- Alopecia commonly on face, shoulders, rump
- Skin normal
- Horse otherwise healthy
- Pathogenesis unknown
- Spontaneous recovery over several months
Describe the cause and appearance of anagen defluxation
- Disease (infectious, metabolic, fever) can disrup the hair cycle leading to sudden hair loss
- Hair shaft breakage
Describe the cause and appearance of telogen defluxation
- Stress (pregnancy, fever, severe illness, surgery, anaesthesia) causes abrupt premature cessation of growth of anagen hairs
- Within 1-3 months a large number of telogen hairs are shed
Describe the treatment of anagen and telogen defluxation
Both spontaneously resolve when inciting cause is corrected
Name the common coat colour changes that may occur in horses
- Leukotrichia/leukoderma
- Vitiligo
- Spotted leukotrichia
- Reticulated
Describe leukotrichia/leukoderma
- Acquired loss of coat colour without loss of skin pigment
- e.g. freeze brand, bandage rub
- Non-progressive
Describe vitiligo
Gradual appearance of non-pigmented skin without other change, e.g. pink periocular areas of arabs
Describe spotted leukotrichia
- Shire, TB, Arab
- Non-inflammatory whitehaired spots on normal skin
- Increased number of static spots
- Commonly seen on chestnuts
Describe reticulated leukotrichia
- white hair patterns
- Can be painful
- Quarter horse, TB, SB
- Cause unknown
- Generally not treated
How can the coat colour conditions of horses be differentiated?
Clinical signs or histopathology of biopsies, but not important as no treatment required for any
