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derm
11/9/98

morris: more allergy stuff

original allergy 
blood test: RAST - radioallergosorbent assay test. 
allergen is bound to 
the bottom of plastic wells. the patient serum is applied to the plastic 
and allowed an incubation period to bind; then plate is washed to remove 
unbound IgE. then anti-IgE Ab is applied. in RAST there is a radioisotope 
involved so it has worker safety implications.

the ELISA is tagged with 
a safer fluorescent tag but is still a similar test. 
the VARL is an 
elisa which suspends allergen in solution instead of binding it to 
plastic plate, but still similar.

the problem for many years with these 
tests was that we didn't have just patient IgE binding allergens. there 
is a lot of crossreactivity with IgG, and non-allergic patients looked 
allergic on these tests. IgG doesn't cause mast cell degranulation and 
Tcell reactivity to allergens. So tests could look positive on 
everything, and that isn't useful at all. but, we didn't need to sedate 
dogs, clip them, or use drug withdrawal. skin tests are expensive to do 
and you have to do a lot of animals to recoup startup costs, and so 
people used these blood tests a lot. 

currently, we get a lot of false 
negatives during the off season. when testing how much IgE is in the 
blood, if the allergen has not been around for 6 mos, the level of Ab 
will be low in the serum - but it stays high in the skin (and pulmonary 
tissues). 

a new test - Heska Corp in Ft Collins CO has made an alpha 
chain IgE receptor test, which more closely mimics the results of 
intradermal testing. if your skin tests are negative, do not submit a 
receptor based test because it is also going to be negative. this test 
*might* replace the skin test. the mfr recommends steroid withdrawal 
prior to testing. the problem again is that in the off season it may not 
be valid if animal is seasonally allergic.

treatment of Atopic 
Dermatitis (AD)
-allergen avoidance if possible - pollens and stuff are 
impossible to avoid
-regular bathing/rinsing to remove allergens from the 
skin and coat
-control secondary infections - huge part of mgmt
-spot 
therapy with topical steroids or anesthetics when applicable

-nonsteroidal antipruritic drugs 
-steroidal antiinflammatory drugs

-immunotherapy with regular rechecks q 1 month and then q 3 mos

if 
infections are present people will sometimes stop using the allergy 
shots, thinking they are not working. 

spot therapy is great in people - 
antihistamine/lidocaine spray - in pets, hard to get them to the skin b/c 
of the fur. 

NSAIDs: H1 blockers - classic antihistamines
-rarely 
helpful used alone
-used with FA supplements, or to decrease needed 
steroid dose
-nonsedating drugs do not work well in dog/cat: probably, 
sedative effect of antihistamines is reason animals scratch less; 
histamine probably isn't the major mediator of itchiness. 
-safe, 
inexpensive
-have to try a bunch of them to see if any work - doses in 
notes

Omega-3-FAs:
-EPA, DHA, GLA (eicosapentaenoic 
acid,docosa-hexaenoic acid, gamma-linolenic acid. 
-incorporated into 
cell membranes, compete for enzymes that metabolize arachadonic acid.

-shift metabolic products of arachadonic acid from proinflammatory to 
antiinflammatory PGs and LTs!! shifts to 12-lipooxygenase pathway from 
COX or 5-lipoxygenase pathway. 
-doses in notes look high - dogs require 
high doses.
-just know FAs shift AA cascade from bad PG to good PG


steroidal antiinflammatory drugs:
-block phospholipase A2, whole AA 
cascade
-decrease production/survival of mast cells and eosinophils, 
important allergy effector cells.
-decrease vascular permeability, cut 
down edema, synergistic with antihistamines and FAs
-topical, oral, 
parenteral
-

indications/dosing of steroids:
-seasonal or episodic 
pruritus
-adjunct therapy for nonseasonal atopy
-goal: lowest possible 
dose and frequency of administration
-parenteral steroids are not 
recommended for use in dogs (depo-medrol) - constant suppression of the 
HPA axis occurs. OK to do this in cats (very resistant to this effect.)


side effects:
immediate: polydipsia, polyphagia, polyuria, tachypnea, 
behavioral changes (snippy dog gets nice, nice dog gets snippy), GI upset

longterm: skin: dermal thinning, comedones, bruising, demodicosis, 
secondary infxns, calcinosis cutis, delayed wound healing
systemic: 
adrenal suppression, muscle wasting, osteoporosis, ligament weakening/ACL 
injuries, steroid hepatopathy, diabetes mellitus, hyperlipidemia, occult 
UTI, potbelly.

monitoring chronic steroid use:
CBC/chem q 6 mos: 
glucose, liver enzymes, electrolytes
u/a and urine culture q 6 mos 
(occult UTI may ascend to kidney)
ACTH stim to evaluate adrenal reserve 
prior to stopping steroids
PE/skin scrapings of any alopecic lesions to 
r/o demodecosis

Immunotherapy (allergy shots)
-AAAI wants to call it 
"allergy vaccine"
-for AD patients that can't be managed with NSAIDs

-MOA: not totally understood - debated in human literature widely

-benefits 50-80% of dogs
-50% of "responders" have no need for steroids

-response takes 3-18 mos (owners percieve enough improvement to continue)

-best for dogs under 5 yrs of age w/less than 5 yrs of clinical disease

-some breeds seem more difficult to hyposensitize - boxer, westie
-10 to 
12 allergens/vial, 2 vials max
-administer SQ - maintenance boosters 
Q7-21 days
-side effects rare - if increased post-shot itching, usually 
respond to decreased dose or pretreatment with antihistamines. client 
administers at home.
-if anaphylaxis occurs, d/c therapy. this is rare. 
much more a problem in respiratory patients, not atopy patients. 

Feline 
Atopy:
no breed or sex predilections (unlike dog). age of onset 6-24 mos 
of age in 75% of cases. less common in cats than man/dog.
pathogenesis 
similar to in dog
up to 25% also concurent food allergy or FAD.

clinical 
features:
-overgrooming and removal of hair - scratching, biting, 
excessive grooming causing alopecia. anterior medial forelimbs, lateral 
hindlimbs to level of hock, feet, belly, face. that's the classic area. 

respiratory signs more common in cats than dogs, but still only about 5% 
of cases. sneezing, asthma, bronchitis, rhinoconjunctivitis.
other 
lesions: rodent ulcers, eosinophilic granulomas, excoriations, miliary 
dermatitis.

slide: rodent ulcer - upper lip eroded away due to dust mite 
allergy
slide: skin over hip where hair has been removed and there are 
thick, red, eosinophilic plaques.

dx catopy (ha ha).dx based on history, 
signs, r/o flea allergy, food allergy, parasitisms, dermatophytosis, 
psychogenic (rare). food allergy is more common in cats so a food trial 
is a good idea. 
intradermal allergy testing in cats: technique and 
interpretation much more difficult than in dogs. still, test of choice. 

serologic testing: feline IgE has been recently identified - unknown what 
role IgG subclasses may play. no good IgE serological test is on the 
market.

tx:
NSAIDS: omega3 FAs, chlorpheniramine, cyproheptadine

steroids: oral preferred, reposital methylpred (depo-medrol) often used 
though try to limit to under 4 inj/year
do not use progestogens - DO NOT 
USE PROGESTOGENS - (ovaban). a lot of people use Ovaban in cats and cause 
irreversible diabetes mellitus. do not use it. it also promotes mammary 
neoplasia. risk is too high.
immunotherapy works better in cats than dogs 
- 75% response rate, faster than in dogs too. usually response in 4-6 mos 
in cats. but it is hard to get a good skin test since cats stress out, 
have adrenal response. 

Food Allergy:

clinical diagnosis and management 
of food allergy in the dog and cat

typically ddx food allergy, flea 
allergy, atopy.

allergy vs intolerance of food:
allergy implies a 
hypersensitivity to an otherwise innocuous foreign substance.
intolerance 
implies a lack of an enzyme required for physiologic or digestive 
process. 
in humans, histamine release from shellfish, peanuts, almonds 
causes an impressive reaction.

clinical history of food allergic 
patient: 
nonseasonal problem from early on (can happen with atopy too).

response to steroids is highly variable. texts say poor response suggests 
food allergy but some atopic animals do not respond to steroids either, 
and a good response to steroids does not rule out food allergy. texts 
lie. it is very variable.

age of onset also very variable. the thing 
with food allergy is it starts sometiems in very young or very old 
animals - under 5-6 mos of age at onset of pruritus == primary ddx food 
allergy. also if over 7 yrs old. 
usually animal has been eating this 
food for months or years before becoming allergic. owners have trouble 
believing this but this is the case. dogs/cats do not get an allergy to 
food they started eating two days ago.

signs: pruritus, papular rash, 
erythema, hairloss, hyperpigmentation, lichenification, 2ry 
infection/staph/yeast, otitis externa.

lesion distribution - canine: 

closely mimics atopy
if they have the problem limited to ear/rear, 
probably food allergy if nonseasonal. 
pinnae, otitis externa, perineum 
usually involved
also feet, groin, axilla, medial/anterior forelimbs, 
face, muzzle, neck

ddx canine: nonseasonal atopy, sarcoptic mange, 
scabies incognito, intestinal parasite hypersensitivity, contact allergy 
esp if limited to feet and perineum - old cement has some allergen in it, 
flea allergy. combination allergy are not unknown. 

noncutaneous signs:

GI: vomiting and/or diarrhea, gassy, flatulent dogs - often dogs show up 
with just GI or just skin signs.
CNS: epileptiform seizures, malaise - 
very rare.
respiratory: asthma like syndrome

cutaneous signs, feline:

severe facial pruritus w/rule out scabies and ear mites
miliar dermatitis

rodent ulcer
eosinophilic plaque/granuloma
feline symmetrical alopecia

otitis externa

lesion distribution, feline:
feet, axilla, anterior 
medial forelimbs, ventral abdomen, inguinal, bald belly, head/neck/face 
lesions

ddx feline:
FAD, nonseasonal atopy, ear mites, notoedric mange, 
scabies, pemphigus foliaceous, chyeletiella

diagnostics: 
blood and skin 
testing are useless. there are companies who will take your money to do 
these tests for food allergy but they are not useful in any species 
including man. so, dx is based on elimination diet followed by 
provocative exposure trial - this is the test of choice. intradermal 
tests are highly unreliable. 

you need good dietary history to choose a 
nonallergic food source - hard to do in older animal with multiple 
owners. there are few novel proteins left. 
elimination diet:
choose a 
nonallergenic food source animal has never been exposed to.
complete and 
balanced commercial diet vs home made
continue for a MINIMUM of eight 
weeks as long as no improvement is noted. 
we want to use commercial 
diets. however, all food mfrs use similar processes and add similar 
preservatives. if pet is allergic to a preservative, or emulsifier, no 
food trial will work. need home-cooked diet, then. those bring uup the 
question of nutritional completeness. we try to give supplements after 
four weeks.

must be very strict with elimination diet. no treats at all 
except treat made of the test diet. no table scraps, no rawhide chews, no 
chewable HW preventative. can be really difficult with young kids in the 
house. 

foodstuff reported as allergenic in dog/cat:

proteins: beef, 
chicken, horse, lamb, rabbit, fish, mice, dairy, egg, soy meal
grains: 
wheat, corn, barley, oatmeal, rice
additives, preservatives, binders, 
coloring agents

chooosing test diet:

novel protein source diets: 
lamb/rice, lamb/potato, venison/rice, venison/potato, rabbit/rice, 
rabbit/potato, fish/potato, veggie

failure to respond to a commercially 
produced diet does *not* - repeat *DOES NOT* rule out food allergy.

home 
cooking choices: difficult. lamb, venison, rabbit, fish, pinto beans, 
tofu, veggi. can have authorities notify you when a deer is found by side 
of road... can buy rabbit in a store but expensive. 
for 8 wk trial: 
vitamin/mineral supplementation is recommended after the first month. 
now, some individuals will respond w/in first 4 weeks. if so, great. no 
vitamin needed. but after that they need to.
cats: obligate carnivore. do 
well with meat only. no taurine addition required.

remove all visible 
fat
cook by boiling so fat boils off
nothing added to water - no 
seasonings!
skim grease
save water for flavoring
mix meat/grain 50-50 for 
dogs
increase amount of carbohydrate until pet is not too hungry
feed a 
few times ad day
rest dogs after eating large amounts to prevent GDV

if 
patient improves but isn't perfect, extend trial. try going out to 12 
weeks. make clients prove it to themselves.

morning after: after 
stabilizing pet, do provocative exposure trial to former diet, or to 
individual items like chicken, beef, wheat, soy, dairy - one at a time. 
can take up to two weeks or longer for pet to react to challenge foods. 
usually though rxn is w/in 2+ hrs.

maintenance: search for commercial 
diet pet can tolerate; may need home cooking for a while. rarely is 
homecooking needed for life except for some cats who can't tolerate any 
commercial foods.

other stuff in allergy notes - won't go over in class 
- won't test on them. just there for the heck of it.

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