Equine Dermatology, Pt. 2 Flashcards
What causes dermatophilosis (rain rot)? What is it associated with?
Dermatophilus congolensis, Gram + opportunistic, non-saprophytic organism
wet weather and poor conditions in young, old, or compromised horses
What lesions are associated with dermatophilosis (rain rot)?
small papules and scabs and expands into painful lesions that can pull off as tufts (paintbrush lesions)
- most commonly found along the back topline or limbs
How is dermatophilosis (rain rot) treated?
- bathe in iodine soap or benzoyl peroxide
- keep affected areas dry
- treat extensive infection with penicillin or TMS
- clean brushes in Clorox
How can dermatophilsos (rain rot) be avoided?
stop animal to animal transmission by…
- avoiding contact between affected and non-affected horses
- avoid sharing cleaning tools and equipment
Dermatophilosis lesions:
rain rot
Dermatophilosis lesion appearance:
paintbrush lesions with hair pulled out
What are the 2 most common causes of dermatophytosis (Ringworm) in horses? How do lesions appear?
ZOONOTIC Trichophyton or Microsporum spp
multiple spots of alopecia with scales, typically not itchy unless there is a secondary infection
How is dermatophytosis (Ringworm) diagnosed? Treated?
fungal culture
- Betadine scrub
- Clorox (1:10 dilution)
- clean equipment and environment
What is thought to cause aural plaques in horses? How do lesions appear?
viral or insect bite hypersensitivity
painful, crust plaques in the ears causes the horses to become resistant to bridling
What are 3 aspects to the treatment of aural plaques?
- Panalog - topical steroid cream
- Dexamethasone, Furacin, DMSO mixture applied daily
- fly mask that includes ears
complete cure is difficult
Aural plaques:
What causes pemphigus foliaceus? How do lesios progress?
Type II hypersensitivity - antibody production against intracellular derma cement
- vesicles, bullae
- scales, crusts
- start on the face, neck, and limbs and then become generalized
How is pemphigus foliaceus treated? What additional treatments may be effective?
- corticosteroids at the lowest effective dose
- treat secondary infections and inflammation
- once the problem is controlled, aim to wean off
gold salts or chemotherapeutics —> consult a dermatologist!
What is anhydrosis? How does it present?
inability to sweat
chronically dry scaly haircoat and heat intolerance
How is anhydrosis diagnosed? Treated?
intradermal terbutaline sweat test
move horse to a cool environment and allow sweating capacity to gradually return as weather warms
What is primary and secondary photosensitization? What are the 2 most common signs?
PRIMARY = consuming photodynamic toxins
SECONDARY = liver disease and failure to metabolize hemoglobin breakdown products
- scaly, crusty lesions with scabs on white-haired areas
- signs of liver disease
What treatment is recommended for photosensitization? How can it be avoided?
glycerol spray to soften skin - 240 mL glycerin/glycerol + 1 L of distilled water applied as needed
- eliminate access to toxic plants
- avoid sun exposure
- bathe and treat skin lesions
What is equine cannon keratosis? What needs to be ruled out? What treatment is recommended?
unknown cause associated with scaling, crusting, and alopecia of the cranial hindlimb cannon
dermatophytosis, dermatophilosis
no cure - shampoos and creams help
How do fly/insect bites affect horses’ skin? What clinical signs are associated?
hypersensitivity to deer flies, horse flies, or mosquitoes
papules, wheals +/- ulcerations most commonly seen in the summer
How are fly/insect bites treated?
- Equitrol
- keep horse in barn during the day with a fan
- fly sheet with insect repellant
- Swat
- treat wounds
What causes wart development in horses? How do they appear?
Equine Papillomavirus, often infecting young horses
keratinized mass
How are equine warts treated?
- usually resolves on its own
- can debulk, remove, or freeze
- old horseman’s method = pick warts
Equine warts:
Papillomavirus
What is nodular necrobiosis?
unknown cause of the development of palpable nodules under the skin, typically found where the saddle sits
- aka Eosinophilic Granuloma Complex
How is nodular necrobiosis diagnosed? Treated?
history (saddle area), biopsy of mass removal
- single lesion: excise mass
- multiple lesions: inject with steroids
What is the most common cause of urticaria? How does it present?
hypersensitivity to medication, soap, fly spray, saddle pad, etc.
rapid onset of raised plaques, making the horse become itchy and uncomfortable
How is urticaria treated?
- pre-treat with antihistamines if contact with a known irritant will likely occur + remove cause of reaction
- administer corticosteroids if a reaction has started
- administer epinephrine if systemic signs, like rapid/shallow breathing, occurs
What are the 3 most common equine dermal tumors? Which one is the most common?
- sarcoid*
- SCC
- melanoma
Where are sarcoids most commonly found? How do they act? What may they be associated with?
head and ears of young adult horses
locally aggressive, but nonmalignant
Papillomavirus
What are the 4 major sarcoid types?
- occult - flat, dry
- verrucous - wart-like
- nodular - no skin eruption
- fibrous - proliferative granulation tissue
Mixed sarcoid:
What is a malevolent sarcoid?
sarcoid that has become extensive due to repeated trauma or surgical intervention
How are sarcoids diagnosed? What are 4 options for treatment?
debulk and submit tissue for histopath
- radiation
- cryotherapy
- topical 5-fluorouracil, imiquimod, or cisplatin (wear gloves!)
- immune stimulants
What signalment is most commonly affected by SCC?
- Appaloosas and other light-colored breeds
- > 5 y//o
What are 3 clinical signs associated with SCC? How does it act?
- non-healing ulcer most commonly seen on non-pigmented skin, especially mucocutaneous junctions
- development into a cauliflower-like mass
- bleeds easily
locally invasive, slow to metastasize
What signalment is most commonly affected by melanoma?
gray, middle-aged or older
- internal and external
- rarely affects non-gray horses
Melanoma:
What 4 unique treatments of melanoma are available for horses?
- surgical removal - tumor rarely grows back, however it does not help with other internal tumors
- Cimetidine - antagonizes H2 receptors on tumor cells, activates the local immune response, and blocks T-cell suppressor cells usually stimulated hy histamine
- vaccines
- interferon immune stimulants
What skin lesions are associated with cutaneous lymphosarcoma? What additional systemic signs can be seen?
subcutaneous lumps and bumps that may change in size
SYSTEMIC FORM
- weight loss
- anemia
- thrombocytopenia
- lymphadenopathy
What treatment may subcutaneous lymphosarcoma respond to?
Prednisolone or Dexamethasone
How does PPID affect equine skin? In what horses is it most commonly seen?
long, thin-haired coat due to delayed shedding
> 15 y/o
What are thermal injuries commonly associated with? What long-lasting effects does this have?
barn fires —> assess lungs too
full-thickness = thin, friable tissue/scarring that can easily be irritated by tack —> requires special padding
When are tick infestations most common? Where on the horse is most affected?
Spring to Fall in horses grazing in long grasses
clusters around the fetlock and tail head
What diseases are associated with tick infestations? How can this be avoided?
Anaplasmosis, Lyme disease
- keep pastures mowed
- use insect repellants
What causes fistulus withers? What is commonly required for treatment?
chronic infection/irritation of the supraspinous bursa, most commonly bacterial (Actinomycose bovis, or zoonotic Brucella abortus) or parasites, mechanical
difficult to resolve —> surgical debridement
In what horses are decubital ulcers most common? How can they be avoided?
down horses or foals, with increased risk with poor nutrition
provide padding (water bed), nutritional support, and a clean environment
In what breeds is Fram Overo Lethal White Syndrome most common?
- American Paint
- American Miniature Horse
- Arabian crosses
- TB
- Crop-out QH
associated with Frame Overo color - color frames body
What causes Overal Lethal White Syndrome? How are horses affected?
autosomal recessive mutation in the endothelin receptor B gene (heterozygote = carrier) —> genetic test for detecting O allele
foals are born normal, white coats and blue eyes, but within 1-2 days colic develops due to ileocolonic aganglionosis
