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Dr Palmer

equine derm

the handout is comprehensive; you 
don't have to know all of this for the exam, though. you only need to 
know what is being discussed today. there are 8 questions from this 
material on the final. 

the most important thing is to be able to 
recognize a disease. if you know what it is, you can find out how to 
treat it. each question has a description of a lesion, then a list of 
diseases - one question per disease. only the diseases being discussed 
here today. he's not going through the handout in order; he's going to 
jump around and cover only the stuff that will be on the exam and 
whatever else he can get to. 

Derm isn't a great money maker in equine 
practice, but it is indirectly. they won't call you out about this, but 
while you're there, they will ask about it and if you can answre 
intelligently, your credibility goes way up. 

you need to see, touch, 
sometimes smell the skin to see what's going on, so don't expect too much 
from these slides. 

Dermatomycosis (p 1) - Ringworm

common but often 
overdiagnosed.
usually in young animals with less developed immune system

focal lesions, circular, usually multiple; often in girth area, hind 
legs, head, periocular.
initially, urticarial swellings- horse breaks out 
in hives -  and then hair falls out, hives go away, and you have these 
other lesions
crusting and scaling occurs
may coalesce into large 
alopecic areas 
these are dry, scaly lesions with hairloss
can be very 
numerous
usually not pruritic, although it can be, but more often is not

slide: severe lesions on a calf

to tell this from dermatophilus - 
ringworm is an environmental contaminant, and in the winter in calving 
pens there may be enough around...(??)

3% Captan (Orthocide) works; 
there are always rumors going around about how it is going off the 
market, causes cancer, this, that, the other thing. This is a product 
used on roses, actually, but it works really well on these animals to 
treat ringworm. you can also spray it on the environment to decrease the 
load. 

Dermatophilosis (p 5)

Rain scald, rain rot, mycotic dermatitis 
(not mycotic though, it's bacterial), streptothricosis. responds well to 
abx, actually.
when organism gets wet, it forms a motile, invasive, 
infectious form and seems to aerosolize. you want to bathe these animals 
but not near uninfected animals.
etiologic agent: dermatophilus 
congolensis (actinomycete)
this bug is an obligate parasite - if it gets 
off the host, it does. however, wet lesions release infective stages, and 
it is carried on wild animals.
this is a disease of "dirty horses." if 
skin is healthy, this won't happen. if horse is used to daily grooming 
and then you skip a few days it can show up. often in horses who are 
turned out all the time. teaching horses tend to have it. 

often has a 
dorsal distribution: rump and top line, saddle area, face and neck, 
sometimes pasterns, coronets, heels. this is generally a mild disease but 
may become severe and when it does, it can be a very inflammatory 
problem, causing depression, lethargy, anorexia, fever, weight loss, 
lymphadenopathy. but generally it is mild, with very small lesions, 
easily taken care of.

often on the neck - at first horse will look dirty 
- feels like matted hair, dirt but really you feel little scabs, from the 
exudate from the lesions. the exudate makes little hair mats there.


moist exudative lesions under a thick crust
skin feels thick, hard
hair 
matted or dry
hair epilates easily - in little chunks, held together by 
scab
roots of hair protrude through underside
removal of crust is painful

moist, exudative lesion is underneath
can be five or six of these or all 
over the side of the animal. 

tx is in handout, won't really discuss 
that
dx - take some scabs. make impression smears, do gram stain - will 
see chains of organisms with side chains at right angles - can mimic 
railroad tracks. sometimes you make a smear and don't see these, but if 
you put scab in a tube with some saline, let it incubate a few hours in 
your pocket, then make a smear, you'll see it. 

Pemphigus Foliaceus (p 
22)

No age, breed, or sex predilection
not rare in horses
probably most 
common derm problem at NBC because it's nonresponsive w/o 
immunosuppressive therapy
lesions often start on side of face, around 
eyes; or legs, rapidly becoming widespread. sometimes starts as dorsal 
dermatitis, or only on coronary band
primary lesions are vesicles and 
pustules which are very transient, gone within hours. then you see 
crusts, scales, oozing lesions.

slide: typical pemphigus face which 
looks much like a ringworm case to me but it's a dark slide. front of his 
face is ok. sides are bad.

can spontaneously resolve without treatment 
but most of the ones we see do not do that, they require a lot of 
therapy, but again we're a referral center. 

often there are lesions on 
the legs.
sometimes it is just on the coronary band - only sign is 
coronitis, with these lesions. localized form.

lesions again can be very 
small, can coalesce, can look like dermatophilus in that they're small, 
crusty/scabby lesions but they are less exudative than dermatophilus.


this mare has generalized dz - can be mild in a couple areas or more 
diffuse like in this pregnant mare who got pemphigus at about month 9 of 
pregnancy, went off feed, got depressed. put her on high doses of 
steroids. she responded well, had her foal. they kept her open that next 
year, weaned her off her meds, got her back in foal, then she got 
pemphigus at 9th month again. owners decided it was too much of a hassle. 
these lesions can be very inflammatory, feel very hot to the touch, and 
are painful to the horse when they are extensive like this. this mare, 
most of her body had these lesions.

some more unusual things...

"Nikolsky sign" in people - also seen in horse - b/c cells aren't 
adherent, can rub skin off easily - pick hair off, and skin underneath 
will come off with mild rubbing. not that common, but can see this 
sometimes - may see skin peeling off.
also horse may have skin that seems 
thin, unusually so - flexing the neck shows creases. this is a part of 
that.

may be pruritic or painful (when mild, not)
may have systemic 
signs: depression, weight loss, anorexia, fever
diagnosis - 
histopathology, "vesicle watch" - students watch the horse every hour, 24 
hrs a day, then do "emergency biopsy" when they find a vesicle; 
immunofluorescence. always make sure to send biopsy to 
dermatopathologist.

sometimes horses with pemphigus will grow in white 
hair at the site of the lesion or have white skin. they will have 
coronitis. 
this horse has dermatitis on head, legs, and coronitis. 
this 
other horse has some lesions on face, ear, muzzle, near eye, and some on 
legs as well, and has a coronitis - proliferation of coronary band. so 
this horse has other signs of pemphigus, but sometimes it's just 
presenting with coronitis. proliferative dermatitis around coronary band 
is seen in this other horse. if there are just lesions around coronary 
band, how do you dx pemphigus? try to biopsy the bulb of the heel. 
this 
horse has granulation tissue or reaction in the frog of the foot.
this 
other horse has a mild coronitis and no other lesions. coronary band is 
inflamed. 

not all coronitis is pemphigus, though. 
here's a weanling 
with a fairly good coronitis, but this is secondary to salmonellosis 
causing thrombosis of microvessels and causing this reaction.

if you do 
see coronitis, pemphigus is one thing to consider.
treatment - steroids, 
aurothioglucose (gold salts). for the gold salts, you usually do a test 
dose to see if there is a bad reaction. in one mini horse tx with gold at 
3 mos, he developed a hepatopathy. some horses don't tolerate the gold 
salts. 

in young horses, we may see resolution of the disease once it is 
controlled - can wean of tx and they often do all right.
in older horses 
more often than not they need lifelong therapy.

Pastern Inflammation (p 
19)
scratches, grease heel
owner often thinks horse has a cut, or rope 
burn. but that's not what it is. it sort of looks like a cut or scratch, 
though. frustrating disease - doesn't respond to therapy well probably 
b/c of many etiologies:
etiology: 
contact dermatitis - horse standing in 
mud all the time, around watering trough that overflows, etc.
pastern 
folliculitis - coag + staph, dermatophilosis, dermatophytes, chorioptic 
mange (pruritic)
contact photosensitization - unpigmented pastern and 
muzzle, contact with certain clovers causes a reaction
photoactivated 
vasculitis - white areas
trombiculidiasis (chiggers) 
pemphigus 
foliaceous

so this long list of different things obviously won't all 
respond to the same thing. if you have a case, try your "standard 
therapy" and if it fails, rediagnose. try to see what exactly it is. 
often it just looks like a dirty pastern but it isn't dirt caked there, 
it's an inflammation, a dermatitis. may see some stocking up, some 
lameness. flexion will make him jog off lame b/c the skin is sore. 


lesions generally occur in the natural folds that occur when you pick the 
foot up. here's one that is more severe - white pastern with 
proliferative crusty lesion
here's another one with a lot of 
inflammation, even b/w bulbs of the heel - very red skin. may need biopsy 
or culture to figure this out. looks like contact problem, though.

here 
is another pemphigus, he presented as pastern dermatitis but when 
clipped, you can see the dermatitis going all the way around - in 
pemphigus it tends to circle whole coronary band; with pastern 
inflammation tends to be in the back. 

Pigment diseases (p 15)


Vitiligo: idiopathic loss of pigment in skin, sometimes hair
Leukoderma: 
loss of pigment in skin due to inflammation
Leukotrichia: loss of pigment 
in hair due to inflammation
Variegated Leukotrichia: more specific type 
of pigment thing

it's nice to know what's going on with these.


Vitiligo:
idiopathic - no associated inflammation
you see a pigmented 
area that isn't pigmented :)
used to be pigmented, or should be pigmented 
but isn't.
seems to be inherited. these horses have some melanocyte 
antibodies but there is no inflammatory lesion with this process. 
may be 
associated with immune mediated disease: there is a problem where animals 
with melanomas get vitiligo due to Ab against the melanoma
arabians have 
a thing called "pinky syndrome."
basically it's a benign, irreversible 
loss of pigment.

Arabian Fading Syndrome, Pinky Syndrome (vitiligo of 
arabian)
in the Arabians, the disease can be very striking and 
devastating to the owner b/c one thing about Arabians is they are 
supposed to have dark skin under their hair, especially around his 
muzzle. this horse has white splotches on his nose and eyes. usually 
shows up about age 1-2. just simple loss of pigment, no inflammation or 
redness or thickening or thinning of skin. you can't do anything about 
this. owners may tattoo the area or put boot polish on the areas so they 
can show the horse. the area may be haired with leukotrichia. there is no 
hair loss. 
during pregnancy/early postpartum
lesions are annular, 
symmetrical, on muzzle, lips, periocular; anus, vulva, sheath, hooves 
affected. may regress within a year or be permanent. may wax and wane.


Leukoderma (p 15)
acquired depigmentation of skin, due to:
trauma (poorly 
fitting saddle causing a lesion)
inflamamtion (onchocerciasis)
herpes 
coital exanthema
pressure sores
pemphigus
ventral midline dermatitis

papillomatosis
contact with rubbers containing antioxidants (inhibit 
melanogenesis)
horses don't get leukoderma as often as other spp do


Leukotrichia (p 15) 
acquired depigmentation of hair (not skin)
may be 
more common on chestnuts
due to trauma, inflammation, may occur at site 
of nerve blocks

when you have a patient you should look and see if there 
are other areas of leukotrichia, and if so, warn owner that whatever 
you're doing may result in another area of it. 

this one chestnut mare 
grew white hair at almost all injection sites. 
most horses aren't that 
sensitive, though.

Variegated Leukotrichia (p 16)
Quarter Horses, 
others. usually b/w whithers and tail.
born w/o this, shows up over time 
but probably inherited
we see it mostly in yearlings, but can see in any 
age
dorsal midline from withers to tail base
sometimes more linear - this 
horse has a tic-tac-toe board on his side, almost. may see state map, 
mickey mouse, whatever. it is usually leukotrichia +/- leukoderma. it's a 
permanent change. 

this pony has white streaks going down his back- 
research pony. he got this white dorsal stripe. he was about 35 yrs old 
when he was brought here and he didn't have this then, but it showed up 
later. there is a linear area of crusting which crusts, crusts fall off, 
and white hair grows in. not white skin. just white hair, usually. it's 
variegated b/c the hairs often have stripes of black and white on them. 


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Drug Eruptions (p 23)
sometimes these are called allergies 
but not all of them are allergies
common causes:
penicillin (most common, 
and most are probably allergies)
phenothiazines
diuretics
bute
sulfas

NSAIDS
local anesthetics
steroids

can occur after 1st dose (so not like 
allergy)
or used for years
most reactions occur 24-48 hrs after dose
some 
within minutes
some up to a week later
can persist as long as six months 
and may not respond well to steroids.

note: this is different from a 
"procaine reaction" seen when people give procain penicillin and 
inadvertently get into a sinusoid or vein -- then, you see the horse fall 
away from the needle, it's that fast, and the horse becomes agitated, 
runs around, falls over, may seizure - that's a reaction to IV procaine. 
we're talking now about a reaction to PCN without procaine (or with) 
which occurs within a few minutes, and most often causes hives all over, 
they come up within minutes, and characteristically they are small and 
they overlap. poor horse has hives on top of hives. this is 
characteristic of the drug reaction, looks like a "relief map." most 
often seen with PCN. generally treat it and it will go away quickly, but 
you should avoid giving another dose of penicillin. not all drug 
eruptions are like this though.

sometimes hives will become established, 
and stay there for 6 mos. Treat with antihistamines, steroids, in general 
hives will respond but drug eruption hives commonly do NOT respond to 
treatment.

this horse had a reaction to acepromazine and became very 
pruritic. in this slide the horse is enjoying being scratched - extending 
head, neck, squaring off nose, looking pleased. this horse was pruritic 
after getting acepromazine for 3-4 days, after each dose. it was 
definitely reproducible. it started about a day after the dose each time.


Nodular Collagenolytic Granuloma (p 17)
nodular necrobiosis, equine 
eosinophilic granuloma
this is what they call a true necrobiosis - 
collagen necrosis with granulomatous reaction to it - eosinophilic type. 
many people say these are reactions to fly bites b/c of the eosinophils, 
but we see more of them in the middle of the winter than in the summer so 
that doesn't make much sense.
these are a reaction to the necrotic 
collagen - 
etiology: hypersensitivity rxn, not insect related. over 
saddle region - trauma?
dorsally distrubted, small, non-ulcerated lesions 
which may occasionally break open and spill a grey, white, caseous core; 
may calcify; very steroid responsive - can put under the lesion locally, 
or give systemically. they will go away, but will come back when you stop 
the steroids. generally over time you will see one to a hundred develop 
on a horse (usually 10-20). then they go away. don't really hurt the 
horse, don't cause  much of a problem. 

one major ddx is habronema - 
those little parasites that crawl around and end up on the back of 
cattle, cattle grubs, leave a little breathing pore - horses can get this 
too - usually eventually develops a hole - about the same size nodule as 
with the NCG but it has a hole. the parasites can be removed but if 
ruptured can cause allergic reaction. you only see the habronema if 
horses are stabled near cattle. this horse had it while stabled at NBC. 
that's another ddx for nodular collagenolytic granuloma. 

Equine 
Axillary Nodular Necrosis (p 18)
another flavor of this
aka "girth galls" 
b/c they are where girth goes
1-5 nodules at girth area/axilla
round, 
well circumscribed, firm
more likely to calcify
usually no alopecia, 
ulceration, or pain
not steroid responsive. 
possible trauma etiology 
from macerating collagen in the girth?
but broodmares get it too, 
sometimes.
although the dorsally distributed NCG nodules respond to 
nodules, these usually do not. you can try, though. often, b/c it is 
calcified - steroids don't fix calcified lesions. only way to fix it is 
to take it out - but it's not in a good spot for that, they are in a high 
motion area. usually they don't hurt the horse but sometimes they want to 
be removed b/c they do rub and hurt the horse. 

Cutaneous LSA (p 25)


any age, but often aged horses
multiple subcutaenous swellings

occasionally dermoepidermal
variable size 1-50 cm
spontaneous regression 
50%
dx is easy - biopsy one of the lumps and find lymphocytes 
(neoplastic). of course, people tend to panic when they find this but at 
least half of these cases - which by the way are usually subcutaneous LSA 
not really "cutaneous" - will spontaneously regress if you do nothing. so 
don't euthanize the horse just because it has lumps. if you have a sick 
horse, that's one thing. but if the lumps are the only problem, wait it 
out. small to large lumps, few to many.
the best thing to do is watch and 
wait. if horse is happy and fine in the retirement field, just leave him 
alone. 

Cutaneous amyloidosis p 18

rare disease
atypical primary 
amyloidosis
multiple 0.5-10 cm nodules
head, shoulders, neck - not 
caudally
also nasal septum lesions
sometimes the nodules come up and then 
disappear and then come up again and stay. not sure what that is all 
about. maybe some reaction is going on that we're not aware of. 
one 
thing that often happens is that there are also lesions on the nasal 
septum. not hard to find, but you have to look for them - just lift the 
nostril edge and you see the lesions in there - looks like dirt on there, 
but it isn't, it's actually thickened, raised skin. this is the problem. 
horses are obligate nose breathers, and if the nasal septum gets thick 
and occludes nostrils, they can't breathe. we've seen this in a number of 
horses - older broodmares, usually. to keep alive til parturation, need 
to put in permanent tracheostomy to let her breathe. then nasal amyloid 
doesn't obstruct the airway. 

horses used to race their whole lives with 
permanent tracheostomies - roarers would be treated this way - works 
fairly well with little maintenance - just suture skin to trachea; they 
often used to put a screen there to keep dirt out. many horses did fine 
this way. it's not that big of a deal, really. 

take home message - look 
in the nose if there are lumps on the horse, to see if there is amyloid 
in the nose.


----above this line - that's the stuff on the test. below 
this line, not on test.

Onchocerciasis: page 11
onchocerca cervicalis - 
lives in ligamentum nucae, makes mmf that get transmitted by culicoides 
from one horse to another.

horse >4 yrs old
this is an allergic reaction 
to dying microfilaria
occurs in horses infected with onchocerca (breeding 
pair), with microfilaria in the skin, which have lived their lives, and 
are dying.
occurs on forehead, mane, neck, and ventral area in the front 
of the horse. 
dermatologists say a lesion on the forehead on the front 
is pathognomonic for onchocerciasis - dr P isn't convinced.
rubbing mane, 
neck, ventral abdomen...
it's also notable that if you treat these horses 
with ivermectin it can cause a reaction - ivermectin kills the mmf - you 
may see some ventral edema as the onchocerca larvae die. ivermectin kills 
the mmf well so if you use it you can control these horses by preventing 
the huge #s of mmf which cause the bad reaction when they die. also 
decreases transmission. so we probably see less of this problem now 
anyway.
this is a very pruritic process. most of what you see isn't the 
reaction to the mmf per se, but the trauma done by the horse trying to 
scratch - rubbed mane, abrasions on neck, ventrum - location of lesion 
depends where mmf are. 

Culicoides Hypersensitivity:  p 10
< 2 yrs is 
usually age of onset
sometimes yearlings, usually some time in first two 
years of life. or within two years of moving into an area
"dorsal 
feeders" - mane and tail involvement
"ventral feeders" - ventral midline 
dermatitis
this is an allergic reaction to the antigens in the culicoides 
saliva
very pruritic - again, the lesions are caused by the horse rubbing

icelandic ponies, especially - in iceland, there are no culicoides b/c of 
the climate. the ponies which have developed from that area and are then 
taken here or to other areas where there are culicoides are exceedingly 
sensitive, right away. they show signs on warm days in the winter just as 
bad as in the middle of the summer b/c even one bite is a trigger. they 
are really really pruritic and have a real problem with this - probably 
they shoudl just live in Iceland, that's a good place for them :)

dorsal 
lesions - head, ears, mane, withers, rump, tail; generalized. 
ventral 
midline lesions

Therapy - can only manage. very frustrating, somewhat 
like FAD in small animals.
try fly control - culicoides like to breed in 
stagnant water and have only a 1/4 mile flight range so if you remove all 
stagnant water, that can be helpful. they like to feed at dusk/dawn and 
through early evening hours so if youstable horse 4 pm to morning, that 
can cut down feeding. they do not like to fly into buildings. the best 
thing to do is put the horse in the middle of the barn, far from the 
windows. screens don't help b/c they are small. you can paint screens 
with insecticides, though, or buy special culicoides screens, or use 
various flysprays or strips on the horse. still, some animals are so 
sensitive they react to one lone bite. even the best control can't 
guarantee zero bites.
medical therapy - steroids, hydroxyzine, 
hyposensitization
as you know, if you are allergic to one thing, you have 
other allergies too. horse may start being allergic to culicoides - but 
horse is going to get onchocerca from culicoides and may be allergic to 
that, too. and other things. hydroxyzine is a great antihistamine for 
itchy horses - in human medicine they use this antihistamine for its 
sedative/antianxiety effects as a preop. the antianxiety effect is at a 
higher dose. anyway it seems this drug is great for itchy horses perhaps 
b/c of the antianxiety effect. 
hyposensitization is difficult b/c 
antigens are regional and when you move the horse you have to start over. 
one sure cure though that owners do not want to hear is find a friend who 
lives 1000 miles away and ship the horse there and he'll be happy for a 
couple of years. really that's the best way to get them to stop itching 
but that's not so practical. 

Ventral Midline Dermatitis p 9
caused by 3 
things
culicoides front to back
onchocerca front to back
hornflies focal 
around the umbilicus
sometimes culicoides produce lesions just right 
along the center of the midline. onchocerca on the other hand are more 
evenly spread so wider side to side but not always.
if you're near cattle 
the hornflies are a problem. they feed right around the umbilical area.

pruritus is severe, they scratch all the time, they can't think about 
anything else. tx ivermectin for onchocerca, steroids, antihistamine, 
management. 

Aural plaques - p 11
ear fungus

small white plaques on 
inner pinna
this is NOT a fungal disease, but is a proliferative dz of 
the skin. asymptomatic. 
lesions are well circumscribed, raised, flat 
plaques, very scaly, with chalky surface that can be scraped away.
horses 
do not scratch, aren't ear shy, don't know these are there.
but owners do 
NOT like them. 

there's nothing that helps these. flies do make it worse 
so using one of those fly masks that goes over the ears will prevent that 
exacerbation, but it won't go away b/c not caused by flies.

some owners 
use boot polish to cover these lesions at horse shows. 

Papillomatosis: 
p 26

warts
viral, usually on the nose
very common in young horses

weanlings to 3 yrs of age
they go away within a few mos.
if it's a 
yearling going to sale or something owner will ask you to do something. 
also owner will want to prevent scarring.
easiest tx - find a large wart, 
sedate the animal, and rip off that wart, grossly. this releases viral 
particles into blood, enhancing immune response to make it go away 
sooner. can make autogenous wart vaccines, too. you do see group 
outbreaks b/c this is viral. 

in older horses there are atypical, 
nonviral warts which are seen anywhere on the body, one or two or several 
thousand of them. these are poorly understood, less pedunculated than 
viral papillomas, and sometimes cause leukotrichia or leukoderma. 


Equine Sarcoid: p 23

most common tumor in the horse
usually in horses < 
4 yrs old
locally aggressive fibroblastic tumor
viral?
predisposition - 
histocompatibility Ag
lesions: verrucous type (warty) - sessile or 
pedunculated; fibroblastic type (like proud flesh) - sessile or 
pedunculated; occult (flat) type

if one horse in barn has sarcoids, 
others may get one. not necessarily contagious, though.
slide: 
cruciferous, proliferative, ulcerated tumor lateral to eye. 
seen near 
eyes, ears. often look like dirty, raised, proliferative areas. 

make 
sure a veterinary pathologist looks at this. human pathologists will call 
it a highly malignant fibrosarcoma. 

can get quite extensive and 
proliferative
there are various txs we won't really get into. 
cryosurgery, BCG techniques.
sometimes they ulcerate, sometimes they 
don't, sometimes they are under the skin. generally you make a dx based 
on clinical experience. if you do want a biopsy, be aware that this can 
make them proliferate more. especially the ones on the ears. 


Habronemiasis: p 12

summer sores, bursautee, bursatti, swamp cancer, 
kunkurs, esponja, granular dermatitis

ddx: bacterial/fungal granulomas, 
sarcoids, SCC, MCT, proud flesh, papilloma
tx: fly control, insecticide?? 
treat as any granulation tissue. ivermectin injectinos. steroids.

recurrence occurs

the lesions do not occur unless horse is allergic to 
habronema. usually occurs when it dies and starts to degenerate.



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