As mentioned in the first article (Feb. 2002) of this series, the presentation of the pruritic dog can be frustrating for
the veterinarian because of the number of possible differential diagnoses.
An example of a focal pericular deep pyoderma.
It cannot be emphasized enough that a detailed history and thorough physical examination is essential in determining the cause
of the pruritus. A detailed history includes age, breed and sex of the affected animal as well as duration of the pruritus,
areas of the body involved, and response to any medications either topical or systemic that have been administered.
A thorough physical examination should include dermatologic procedures such as combings, skin scrapings and cytology of any
lesions present. Depending upon the outcome of these in-house tests, other laboratory procedures such as complete blood counts,
serum profiles, thyroid panels, tests for Cushing's disease, allergy testing or performing skin biopsies may be necessary.
In part one, differentials of pruritus that included ectoparasites were discussed. Now that in-house testing and/or therapy
to rule out this category have been performed, the next step is to rule out bacterial pyoderma (primary or secondary), atopy
and/or food allergy as the possible cause of pruritus.
In the canine, bacterial pyoderma, the majority of the time, is caused by Staphlococcus intermedius. That is why many veterinarians
do not feel the need to routinely culture a bacterial pyoderma. However, the time when a culture and sensitivity is necessary
is when the patient is not responding to an appropriate antibiotic (assuming antibiotic only is used, not in conjunction with
steroids) or when a deep pyoderma is present, particularly, when demodicosis is involved.
Labrador Retriever with inhalant allergy. The other differential would be scabies because of the ear-edge involvement.
In the latter, many types of bacteria may be present including Pseudomonas and Proteus species. The diagnosis of bacterial
pyoderma is usually made by clinical presentation, i.e. the appearance of pustules or epidermal collarettes.
When intact pustules are present, cytology should be performed revealing results consistent with bacterial pyoderma such as
degenerative neutrophils with or without intracellular cocci. The main differential for bacterial pyoderma is pemphigus foliaceus
which, at times, may be difficult to differentiate for both the clinician and pathologist. In older patients, epitheliotropic
lymphoma may appear clinically similar to bacterial pyoderma. A skin biopsy is necessary to differentiate between the two
In a "first time" bacterial pyoderma, antibiotics such as sulfa derivatives (use with caution in patients with keratoconjunctivitis
sicca (KCS), those breeds prone to KCS, or in Dobermans which can show a possible genetic predisposition for adverse reactions
to sulfas), cephalosporins, macrolides such as lincomycin, or b-lactamase potentiated amoxicillin (Clavamox) should be administered
until total clearing of the pyoderma plus an additional week past clearing. Antibacterial bathing should also be performed.
Tetracyclines and penicillins normally are not effective in treating canine staph pyoderma. Steroids should be avoided even
if the patient is pruritic as they may cause immunosuppression thereby "undoing" the effects of the antibiotic. Normally 21
to 30 days of antibiotic is initially dispensed with a recheck at the end of that period of time to be sure the pyoderma is
resolving, then additional antibiotic is dispensed to complete the "one week past clearing" process. Antibacterial shampoos
such as chlorhexidine, ethyl lactate (Etiderm), benzoyl peroxide or sulfa/salicylic acid combinations can be helpful adjunctive
therapy. In a recurrent pyoderma, factors to consider include: Was the pyoderma treated with an appropriate antibiotic without
steroids until one week past clearing? Is there a potentiating underlying disease such as demodicosis, hypothyroidism, Cushing's
disease, diabetes mellitus, atopy or food allergy? Treatment of a recurrent pyoderma involves antibiotics, antibacterial bathing
and addressing the underlying disease perpetuating the pyoderma.
Periocular alopecia and erythema in an atopic Boston Terrier.
If no underlying disease is found, then "pulse dosing" antibiotics i.e. one week on/one week off is performed or immune stimulants
such as Staphage Lysate are administered.
Food allergy can manifest with many symptoms including a recurrent bacterial pyoderma, otitis, Malassezia dermatitis and pruritus
without lesions. Dogs of any age, breed or sex can be affected. Some dermatologists classify food allergic dogs as having
symptoms involving "ears and rears".
Nondermatologic manifestations of food allergy can include gastrointestinal problems such as vomiting, diarrhea, and flatulence,
respiratory problems or neurologic symptoms including seizures. Food allergic patients usually have nonseasonal problems since
they are eating the same food all of the time (or variations of the same food) and are nonresponsive to antipruritic doses
of steroid (however some patients may get temporary relief from anti-inflammatory or immunosuppressive doses of steroid).
Since blood or skin testing for food allergy has not been proven to be accurate, the best way to assess food allergy in the
dog is the feeding of a hypoallergenic diet either cooked or commercially prepared for at least eight to 10 weeks and perhaps
longer. The favored method is a home-cooked diet consisting of a novel protein and single carbohydrate source.
Since this is impractical for most large breed dog owners, commercially available prescription foods containing novel proteins
such as venison, rabbit, duck, fish, kangaroo or a protein hydrolysate diet are available. The concept of what one is trying
to accomplish must be explained to the owner so that the diet is performed correctly.
The point is to remove the pet from all ingredients to which they have been exposed to in previous foods or treats e.g. corn,
wheat, egg, beef, chicken, soy and dairy. No other foods, bones, rawhides, treats or flavored heartworm preventatives should
be administered during the diet period.
Erythemic alopecia caudal in an atopic patient.
Some owners elect to administer distilled water as opposed to tap water to further control what the animal is receiving. It
may be difficult to undertake a hypoallergenic diet for owners with young children since theoretically a dietary indiscretion
can set the patient back one to two weeks. Since there are two categories of hypoallergenic diets, the single allergen diet
and the protein hydrolysate diets, a patient may respond to one type of diet and not the other. If you have undertaken a hypoallergenic
diet of one particular type without success, be sure to feed one of the other category to fully rule out food allergy. Be
extremely inquisitive about what is administered to the patient i.e. medications cannot be given with cheese, lunch meats
or peanut butter (contains corn syrup) which will negate the effect of the diet.