Equine Dermatology, Pt. 2

Question 1

What causes dermatophilosis (rain rot)? What is it associated with?

Answer 1

Dermatophilus congolensis, Gram + opportunistic, non-saprophytic organism

wet weather and poor conditions in young, old, or compromised horses

Question 2

What lesions are associated with dermatophilosis (rain rot)?

Answer 2

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

Question 3

How is dermatophilosis (rain rot) treated?

Answer 3

• bathe in iodine soap or benzoyl peroxide
• keep affected areas dry
• treat extensive infection with penicillin or TMS
• clean brushes in Clorox

Question 4

How can dermatophilsos (rain rot) be avoided?

Answer 4

stop animal to animal transmission by…

• avoiding contact between affected and non-affected horses
• avoid sharing cleaning tools and equipment

Question 5

Dermatophilosis lesions:

Answer 5

rain rot

Question 6

Dermatophilosis lesion appearance:

Answer 6

paintbrush lesions with hair pulled out

Question 7

What are the 2 most common causes of dermatophytosis (Ringworm) in horses? How do lesions appear?

Answer 7

ZOONOTIC Trichophyton or Microsporum spp

multiple spots of alopecia with scales, typically not itchy unless there is a secondary infection

Question 8

How is dermatophytosis (Ringworm) diagnosed? Treated?

Answer 8

fungal culture

• Betadine scrub
• Clorox (1:10 dilution)
• clean equipment and environment

Question 9

What is thought to cause aural plaques in horses? How do lesions appear?

Answer 9

viral or insect bite hypersensitivity

painful, crust plaques in the ears causes the horses to become resistant to bridling

Question 10

What are 3 aspects to the treatment of aural plaques?

Answer 10

1. Panalog - topical steroid cream
2. Dexamethasone, Furacin, DMSO mixture applied daily
3. fly mask that includes ears

complete cure is difficult

Question 11

Aural plaques:

Answer 11

Question 12

What causes pemphigus foliaceus? How do lesios progress?

Answer 12

Type II hypersensitivity - antibody production against intracellular derma cement

• vesicles, bullae
• scales, crusts
• start on the face, neck, and limbs and then become generalized

Question 13

How is pemphigus foliaceus treated? What additional treatments may be effective?

Answer 13

• 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!

Question 14

What is anhydrosis? How does it present?

Answer 14

inability to sweat

chronically dry scaly haircoat and heat intolerance

Question 15

How is anhydrosis diagnosed? Treated?

Answer 15

intradermal terbutaline sweat test

move horse to a cool environment and allow sweating capacity to gradually return as weather warms

Question 16

What is primary and secondary photosensitization? What are the 2 most common signs?

Answer 16

PRIMARY = consuming photodynamic toxins

SECONDARY = liver disease and failure to metabolize hemoglobin breakdown products

1. scaly, crusty lesions with scabs on white-haired areas
2. signs of liver disease

Question 17

What treatment is recommended for photosensitization? How can it be avoided?

Answer 17

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

Question 18

What is equine cannon keratosis? What needs to be ruled out? What treatment is recommended?

Answer 18

unknown cause associated with scaling, crusting, and alopecia of the cranial hindlimb cannon

dermatophytosis, dermatophilosis

no cure - shampoos and creams help

Question 19

How do fly/insect bites affect horses’ skin? What clinical signs are associated?

Answer 19

hypersensitivity to deer flies, horse flies, or mosquitoes

papules, wheals +/- ulcerations most commonly seen in the summer

Question 20

How are fly/insect bites treated?

Answer 20

• Equitrol
• keep horse in barn during the day with a fan
• fly sheet with insect repellant
• Swat
• treat wounds

Question 21

What causes wart development in horses? How do they appear?

Answer 21

Equine Papillomavirus, often infecting young horses

keratinized mass

Question 22

How are equine warts treated?

Answer 22

• usually resolves on its own
• can debulk, remove, or freeze
• old horseman’s method = pick warts

Question 23

Equine warts:

Answer 23

Papillomavirus

Question 24

What is nodular necrobiosis?

Answer 24

unknown cause of the development of palpable nodules under the skin, typically found where the saddle sits

• aka Eosinophilic Granuloma Complex

Question 25

How is nodular necrobiosis diagnosed? Treated?

Answer 25

history (saddle area), biopsy of mass removal - single lesion: excise mass - multiple lesions: inject with steroids

Question 26

What is the most common cause of urticaria? How does it present?

Answer 26

hypersensitivity to medication, soap, fly spray, saddle pad, etc. rapid onset of raised plaques, making the horse become itchy and uncomfortable

Question 27

How is urticaria treated?

Answer 27

- 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

Question 28

What are the 3 most common equine dermal tumors? Which one is the most common?

Answer 28

1. sarcoid* 2. SCC 3. melanoma

Question 29

Where are sarcoids most commonly found? How do they act? What may they be associated with?

Answer 29

head and ears of young adult horses locally aggressive, but nonmalignant Papillomavirus

Question 30

What are the 4 major sarcoid types?

Answer 30

1. occult - flat, dry 2. verrucous - wart-like 3. nodular - no skin eruption 4. fibrous - proliferative granulation tissue

Question 31

Mixed sarcoid:

Answer 31

Question 32

What is a malevolent sarcoid?

Answer 32

sarcoid that has become extensive due to repeated trauma or surgical intervention

Question 33

How are sarcoids diagnosed? What are 4 options for treatment?

Answer 33

debulk and submit tissue for histopath 1. radiation 2. cryotherapy 3. topical 5-fluorouracil, imiquimod, or cisplatin (wear gloves!) 4. immune stimulants

Question 34

What signalment is most commonly affected by SCC?

Answer 34

- Appaloosas and other light-colored breeds - > 5 y//o

Question 35

What are 3 clinical signs associated with SCC? How does it act?

Answer 35

1. non-healing ulcer most commonly seen on non-pigmented skin, especially mucocutaneous junctions 2. development into a cauliflower-like mass 3. bleeds easily locally invasive, slow to metastasize

Question 36

What signalment is most commonly affected by melanoma?

Answer 36

gray, middle-aged or older - internal and external - rarely affects non-gray horses

Question 37

Melanoma:

Answer 37

Question 38

What 4 unique treatments of melanoma are available for horses?

Answer 38

1. surgical removal - tumor rarely grows back, however it does not help with other internal tumors 2. Cimetidine - antagonizes H2 receptors on tumor cells, activates the local immune response, and blocks T-cell suppressor cells usually stimulated hy histamine 3. vaccines 4. interferon immune stimulants

Question 39

What skin lesions are associated with cutaneous lymphosarcoma? What additional systemic signs can be seen?

Answer 39

subcutaneous lumps and bumps that may change in size SYSTEMIC FORM - weight loss - anemia - thrombocytopenia - lymphadenopathy

Question 40

What treatment may subcutaneous lymphosarcoma respond to?

Answer 40

Prednisolone or Dexamethasone

Question 41

How does PPID affect equine skin? In what horses is it most commonly seen?

Answer 41

long, thin-haired coat due to delayed shedding >15 y/o

Question 42

What are thermal injuries commonly associated with? What long-lasting effects does this have?

Answer 42

barn fires ---> assess lungs too full-thickness = thin, friable tissue/scarring that can easily be irritated by tack ---> requires special padding

Question 43

When are tick infestations most common? Where on the horse is most affected?

Answer 43

Spring to Fall in horses grazing in long grasses clusters around the fetlock and tail head

Question 44

What diseases are associated with tick infestations? How can this be avoided?

Answer 44

Anaplasmosis, Lyme disease - keep pastures mowed - use insect repellants

Question 45

What causes fistulus withers? What is commonly required for treatment?

Answer 45

chronic infection/irritation of the supraspinous bursa, most commonly bacterial (Actinomycose bovis, or zoonotic Brucella abortus) or parasites, mechanical difficult to resolve ---> surgical debridement

Question 46

In what horses are decubital ulcers most common? How can they be avoided?

Answer 46

down horses or foals, with increased risk with poor nutrition provide padding (water bed), nutritional support, and a clean environment

Question 47

In what breeds is Fram Overo Lethal White Syndrome most common?

Answer 47

- American Paint - American Miniature Horse - Arabian crosses - TB - Crop-out QH associated with Frame Overo color - color frames body

Question 48

What causes Overal Lethal White Syndrome? How are horses affected?

Answer 48

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