At one time or another, we have all made the same mistakes when working up a dermatology case. To help us all save time and
get the most information with the least amount of work, I thought I would address what in my referral practice appear to be
the most commonly made mistakes when working up a dermatology patient. Some mistakes involve medications and the frequency
of their use while others can be avoided by just spending an extra second or two that, in the long run, will pay off in reaching
the correct diagnosis.
1. Include a history when submitting skin biopsies.
Put yourself in the pathologist's shoes-- that person is only seeing a 6 mm piece of skin whereas you are seeing the complete
picture. It is extremely difficult for the pathologist to interpret what he/she is seeing and come to a conclusion when they
are not given a brief history of the patient which should include age, breed, sex, clinical appearance, duration of the problem
and response to medications. A Polaroid picture accompanying the biopsy sample is submitted by some veterinarians which can
also be helpful.
2. Ivermectin when used for demodicosis is used daily not weekly.
I often get referrals of patients with generalized demodicosis that have been treated with a single injection of ivermectin
or weekly injections (Photo 1). Weekly ivermectin treats scabies, daily ivermectin treats demodex. And of course, when using
ivermectin, dogs must be heartworm negative and not be of a herding breed. I also avoid ivermectin use in elderly patients
as I have had patients with neurological side effects in geriatric non-herding breeds. The dose of ivermectin used daily for
generalized demodicosis is 200ug/kg/day-800ug/kg/day (off-label use).
Photo 1: Patient with generalized demodicosis.
3.Ear cultures are not the same as ear smears.
An ear smear is a quick three-minute procedure that allows you to readily determine what kind of otitis is present i.e. bacterial
vs. yeast (Photo 2). Very simply, an ear smear is performed by obtaining a sample of the ear discharge, rubbing it onto a
glass slide, heat fixing, then staining with Dif Quik or Gram's stain. It is then observed under oil and yields either yeast
or bacteria. If bacteria are present they are usually cocci (BB shaped) or rods (rod shaped). If rods are present, a culture
and sensitivity is then submitted. There are times when a culture and sensitivity is indicated such as when rod bacteria are
present or when current therapy is not effective. However most often the added expense of a culture and sensitivity can be
avoided by checking a quick ear smear first. If you're not used to performing ear smears -- get started! The more you do,
the better you'll get.
Photo 2: Cocker Spaniel with chronic yeast otitis.
4. Perform skin scrapings and combings on all dermatology cases.
This should be automatic. While the owner is giving me the history on the patient, I am combing or scraping the pet (Photo
3). Sometimes when you least expect it, just this little procedure yields surprising results -- such as Demodex gatoi in the
cat or Cheyletiella in the dog.
Photo 3: Cat with Demodex cati.
5.If you suspect scabies, treat for it.
We have all missed scabies at one time or another as early scabies presents with little or no lesions, just pruritus (Photo
4). The most common time scabies is missed is in a middle aged or elderly patient that has just become pruritic for the first
time in their life. The other main differential, atopy, does not usually start in middle age but much younger i.e. 6 months
to 3 years of age. Most patients with scabies are unresponsive to antipruritic doses of steroid. It makes more sense to rule
out scabies first with a month's worth of therapy than to perform skin or blood testing for allergy with a resultant life
time of immunotherapy. Therapy for scabies includes lime dips every five to seven days or ivermectin 200ug/kg/wk x four to
six weeks or milbemycin oxime l mg/kg qod x 16 days or selamectin one dose every 15 days for three doses as well as treatment
of the environment. Scabies or Cheyletiella mites should come to mind particularly if the owners are pruritic.
Photo 4: Excessive face rubbing due to canine scabies.
6. The test for food allergy is a hypoallergenic diet trial.
Unfortunately, skin or blood testing for food allergy has not been shown to be accurate (Photo 5, p. 5). The patient must
be fed a cooked or commercially prepared diet that does not contain any ingredients to which they have already been exposed
i.e. no corn, wheat, egg, beef, chicken, soy, dairy or lamb if they have been on a lamb and rice preparation. It is not enough
to change from a current diet to one with "lamb and rice". In food allergy, it is more important to be sure what is not in
the food than what is in the food. Unfortunately, a lot of owners read incorrect information about food allergy as I hear
daily that dogs are "corn allergic" so they took the patient off of all corn. Corn may be an offending allergen but so can
one or more of the seven other ingredients listed above. Most owners do not understand that one "little treat" will cause
any problems or they continue to administer medications with cheese or peanut butter -- both are not permitted on a hypoallergenic
Photo 5: Food allergic dogs need to placed on a stringent diet that rules out specfic ingredients such as corn, wheat, egg
7. Treat a bacterial pyoderma without steroids.
Even a small dose of steroid can serve to cause immunosuppression and not allow the pyoderma to resolve adequately (Photo
6). Pyoderma is pruritic in some patients, but resist the urge to administer steroids to relieve the pruritus while treating
the pyoderma with antibiotics. Instead use antibacterial or antipruritic shampoos along with antihistamines to help relieve
the itching while treating until at least a week past clearing with antibiotics. It only takes a tiny dose of steroids in
some patients to not allow the pyoderma to resolve.
Photo 6: Bacterial pyoderma on the ventral abdomen.