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Expert Views from a Roundtable on Atopic Dermatitis
Dermatology Roundtable Part 1
Allergy & Topical Therapy:
The Role of Skin Barrier
Dysfunction & Infection
Advances in elucidating
the functions and
dysfunctions of the skin
coupled with emergence
of antibiotic-resistant
bacteria have changed
the face of therapy for
patients with atopic
dermatitis. This
discussion covers the
latest strategies in
effective management
of this troublesome
condition and their
rationale.
Dr. Thomas: Human medicine has seen
an increase in the number of allergic
patients over the past several years.
Have you observed a similar trend?
Dr. Angus: We’ve seen a transition in some
breeds over the last 10 to 15 years, with the
French bulldog leaping to the front of the pack
as far as atopic dermatitis. I think that speaks
to the fact that there are not only environmental factors but also genetic ones at play.
Dr. Plant: It is difficult for somebody in specialty practice to assess prevalence as we tend to see
the same allergic dogs repeatedly. But there
probably has been some increase.
Dr. Thomas: Have you seen an increase
in other dermatologic conditions?
Dr. DeBoer: I think we’re all seeing changes
in pyoderma and in resistant organisms in
general—more resistant staphylococci and
Pseudomonas. The overuse of antibiotics has
complicated all of our jobs a lot.
Dr. Thomas: Do dogs and cats suffer
from methicillin-resistant Staphylococcus aureus (MRSA) or MRSA-equivalent
infections?
1 • clinician’s forum
PARTICIPANTS
John Angus, DVM, DACVD
Veterinary Dermatologist
Animal Dermatology Clinic, Pasadena, CA
Douglas DeBoer, DVM, DACVD
Professor of Dermatology
University of Wisconsin-Madison School of
Veterinary Medicine
Madison, Wisconsin
Valerie Fadok, DVM, PhD, DACVD
Veterinary Dermatologist
North Houston Veterinary Specialists
Spring, Texas
Jon D. Plant, DVM, DACVD
Veterinary Dermatologist
SkinVet Clinic
Lake Oswego, Oregon
MODERATOR
Ursula Thomas, DVM, DACVD
Veterinary Dermatologist
Angell Animal Medical Center-West
Waltham, Massachusetts
Dr. DeBoer: That’s really an emerging topic.
First, it’s very important that veterinarians and
clients understand and use the terminology correctly. We should always make sure that clients
understand that MRSA refers specifically to
Staphylococcus aureus, the human staphylococcal strain, and that methicillin-resistant Staphylococcus pseudintermedius, or MRSP, is the
animal strain that’s prevalent in dogs and sometimes cats.
Dr. Angus: I would say over the last 10 to 15
years, the incidence of MRSA in dogs has remained relatively flat, while the incidence of
MRSP has skyrocketed. Probably 40% of the
patients I see are currently infected with MRSP.
Dr. Fadok: We don’t culture much MRSA from
dogs, but I culture quite a bit from cats. Usually
Skin barrier
dysfunction (left)
is characterized
by allowing entry
of elements that
would normally
be prevented.
those are very inflammatory lesions. Five years
ago in Houston, we still had several options for
dogs with MRSP, but now MRSP is reported as
sensitive to only three antibiotics: amikacin,
mupirocin, or rifampin. Mupirocin may not be
widely used in general veterinary practice, but it
has been in veterinary dermatology. I now use
mupirocin only for methicillin resistant infections.
Dr. DeBoer: One of the first implications of
this resistance is that it’s changing our treatment. When a staphylococcal strain is methicillin-resistant, it’s resistant to all of the beta-lactam
antibiotics, including all penicillins and cephalosporins. It may still be susceptible to other
antibiotic classes, but it becomes necessary to
do more culturing, which gets expensive.
Dr. Plant: Aside from the public health concern about a dog with MRSP, it’s very challenging to the owner.
Dr. Fadok: Another concern is our lack of
knowledge about pyoderma treatment duration. If it doesn’t improve, should we treat it
longer? If it’s not better in four weeks on cephalexin, will treating for 8, 12, or 16 weeks really
make a difference?
Dr. DeBoer: I agree, and especially if new lesions are appearing during antibiotic treatment:
that’s a warning sign that something is wrong.
Dr. Angus: I’ve really changed the way I’m prescribing. I actually go for much shorter courses
than what I was taught in school. I always combine the antibiotic with a topical antiseptic like
chlorhexidine, which accelerates the elimination of the wild-type Staph that is causing the
pyoderma, but also hopefully provides some
backup to the antibiotic so that we aren’t acquiring a methicillin-resistant infection.
Dr. DeBoer: Practitioners also need to be aware
of the transmissibility implications. If it’s MRSP,
we know it’s not generally a human health hazard, but we don’t want that patient in areas of the
clinic where it may be transmitted to other animals. On the other hand, if it’s MRSA, you can
become colonized by touching your face. The
animal can serve as a reservoir for that very resistant human strain in the household, and the
owner has to be informed of that.
Dr. Thomas: What are key factors for the
successful management of bacterial
skin infections in dogs and cats?
Dr. Angus: There is always an underlying cause
in a bacterial skin infection. You can’t treat bacterial folliculitis as a diagnosis rather than a
clinical sign.
Dr. Fadok: It’s important to have a short-term
plan for treating the active infection and a longterm plan devoted to preventing recurrence.
But identifying the underlying cause is, ultimately, that key to success.
ALLERGIC DERMATITIS
& SKIN BARRIER DYSFUNCTION
Dr. DeBoer: Many dogs have “mild” or atypical allergic disease, maybe resulting in recurrent
inflammatory yeast otitis. Once the infection is
gone, the dog seems comfortable, but the presence of the allergic disease causes the infections
to come back. Those dogs need some kind of
management for chronic allergic disease.
This is our wakeup call.
We have to get a grip
on the underlying cause
of these resistant
diseases, and we have
to implement effective
topical therapy. Each
time the infection
comes back, we’re
going to have to culture
it. Otherwise we’ll lose
the one or two
antibiotics we have left.
—Dr. Fadok
Dr. Angus: Until we learned about epidermal
barrier dysfunction as a key mechanism in the
pathogenesis of atopic disease, we didn’t understand why dogs get so many skin infections.
Now we understand that epidermal barrier defect is almost inseparable from the progression
of atopic dermatitis with age and Staph coloniclinician’s forum • 2
For me, the “Aha!”
moment that
connected bacterial
pyoderma and atopic
disease in dogs was
reading human
research that showed
diminishing ceramide
levels in both lesional
and non-lesional atopic
skin compared with
non-atopic skin. One of
the factors implicated
was sphingosine:
zation on the skin. Early recognition of the role
of staphylococci and yeast in atopic dermatitis
should translate to aggressive management to
reduce colonization of the skin. Topical emollients and ceramides and pro-ceramides should
also be used to repair that epidermis.
So we start to progress from a normal-looking
dog to an armadillo in our West Highland white
terriers and Scottish terriers. That lichenification appearance of the skin is a response pattern
to what I suspect to be a really defective epidermal barrier.
Dr. Thomas: Can you elaborate on the
connection between the skin barrier
and allergic dermatitis?
WHY TOPICAL THERAPY?
Dr. Angus: First, the stratum corneum is a
very important permeability barrier. It prevents the exit of water, but also prevents entry
of allergens and irritants, along with things like
yeast and staphylococci. Second, studies have
shown that the epidermis produces antimicrobial peptides that are important to preventing
infection. I think of it as a permeability barrier
and an antimicrobial barrier.
Dr. Thomas: How can we measure if
there is actually a defect in the skin?
Dr. Fadok: We infer the presence of a defect
based on hot, dry skin or excessive scale formation. A tool we traditionally used in research is
assessment of transepidermal water loss.
sphingosine levels
Dr. Angus: One thing to look at is what happens to the skin when you create a defect in the
barrier. You get increased epidermal turnover
and more rapid proliferation of the keratinocytes. As the skin barrier worsens, it adapts by
getting thicker. Atopic dog skin certainly looks
different from normal skin, particularly if you
have added in a couple of secondary infections.
went down, Staph
3 Keys to Managing Bacterial Folliculitis
colonization went up.
1. Not all pyoderma is bacterial, so confirm
your diagnosis. Demodicosis, pemphigus
foliaceus, dermatophytosis, and
Malassezia dermatitis are all frequently
mistaken for bacterial folliculitis.
atopic patients had a
two-fold reduction in
epidermal sphingosine
compared with nonatopic individuals. As
­—Dr. Angus
2. Bacterial skin infections always have an
underlying cause. Treating only the
infection without managing the underlying
disease is like treating pneumonia with a
cough suppressant.
3. A dog can never be bathed too often.
Topical therapy is critical to not only
resolving the current infection but also
preventing relapse. Appropriate antibiotic
therapy should be coupled with frequent
bathing: two to three baths per week
during active infections, and then once a
week thereafter for prevention.
3 • clinician’s forum
Dr. Thomas: How important is topical
therapy for the management of these
complicated skin diseases?
Dr. Fadok: It’s absolutely critical that we teach
owners the importance of bathing their dogs
with skin disease. Often I think there are old
misconceptions that bathing will damage the
coat or the skin, but we didn’t always have the
quality products we have now. If an owner is
willing to bathe multiple times a week, great—
but now we have a topical product for every client. We’ve got sprays, mousses, and for focal
lesions wipes and spot-ons. I think that’s of
great value.
Dr. Angus: Many clients will only use antiseptic shampoo during the active infection, and
then go back to their regular grooming routine
once every six to eight weeks. But with chronic allergic skin disease, continuing to bathe
that dog once a week is a very important.
Dr. Plant: Actually, 20 years ago, we really did
view topical therapy as a kind of adjunct therapy. But there were many times where I’d treat a
patient with pyoderma with antibiotics and
think the owner is probably not going to bathe
this big plush-coated dog in January when it’s
snowing outside. So I’d skip the bathing, thinking the antibiotics will do the job. I’ve really
turned around 180 degrees. Topical therapy has
become really important with the advent of antimicrobial-resistant Staph strains. A lot of times,
owners don’t realize the importance of the topical therapy until they stop doing it.
Dr. Angus: It’s vital that we engage with our
clients to understand what obstacles they’re
facing to the therapies that we recommend.
You can’t tell somebody in their 80s with an
Akita to bathe their dog twice a week and expect that they are going to be able to comply.
Provide solutions. Tell the client: Bring your
dog to us and we can provide that service.
“Well, it costs too much.” We could package
ten baths and charge you for seven. We also
We’re discovering that atopic
dermatitis is a group of
diseases that may vary
substantially from breed to
breed. It explains in part why
it’s so difficult to treat.
—Dr. DeBoer
have mousses and sprays that are certainly better than doing nothing.
Dr. Fadok: I usually bathe them there before
they go home, and it’s great.
Dr. Thomas: For which dermatologic
conditions do you strongly encourage
your clients to use topical therapy?
Dr. Angus: Directly applying therapeutics to
the skin allows us to use these topicals like a
drug instead of relying solely on systemic therapy. The condition that comes to mind most
readily is MRSP. I’m now convinced that bathing is not just an adjunctive therapy, it’s essential
to helping them get better. Sometimes we’re left
with something like amikacin injectables as the
only rational systemic antibiotic. I would much
rather bathe that dog. A less-common disease
where I frequently use topical therapy is demodicosis. The act of bathing and cleaning the
skin, getting the crust off, opening up the hair
follicles, and draining the skin can be very important. Less commonly, sebaceous adenitis responds very well to topical therapy.
Dr. DeBoer: Is it sufficient to get a topical
product of any kind onto the skin, or is it necessary to have the detergent action of the bath?
Dr. Fadok: Initially, a bath is critical because
the sudsing helps to remove the crusts and matted hairs and things that tend to accumulate on
the skin. But if we do that in our clinic, we take
the onus off the client. Then we can send them
home with a topical antiseptic, or if we’re not
treating an infection, a topical lipid. Then we
could follow up with a spray or a mousse.
5 Common Underlying
Causes of Bacterial Folliculitis
• Demodicosis
• Endocrine skin diseases including
iatrogenic or endogenous Cushing’s
disease, or hypothyroidism
• Poorly controlled flea allergy dermatitis
• Atopic dermatitis associated with either
environmental or food allergens or both
I’ve really turned
• Other allergic skin disease
around 180 degrees.
Topical therapy
Dr. Fadok: There’s a bewildering array of topicals available. If you’re going to buy an antiinfective shampoo, get one with lipids, a good
veterinary product that contains chlorhexidine.
Dr. Angus: One of the reasons we all use chlorhexidine shampoos is because it’s the one product that has residual antiseptic activity.
Dr. DeBoer: I agree, chlorhexidine! However,
we have to recognize that there’s no evidence
that 4 % chlorhexidine is better than 2 %. When
you’re selecting a chlorhexidine shampoo, look
at its emollient capabilities, barrier repair, and
how well it lathers. We want to select products
clients are going to enjoy using on their pet.
Dr. Angus: If they’re coming back to get more,
that’s self-reinforcing. You do need to have more
than one product on your shelf, because invariably you will get that one in a thousand bad reaction. And sometimes chlorhexidine isn’t the
answer. The product that the veterinarian has
the most confidence in is the one clients are going to use, because that will come across.
SELECTING A TOPICAL PRODUCT
Dr. Thomas: How do you choose the
right product for the condition?
has become really
important with
the advent of
antimicrobial-resistant
Staph strains.
—Dr. Plant
Tips for a Good Bath
• Use tepid or cool water
• Use mild grooming
shampoo first if coat
debris is plentiful
• Begin medicated
shampooing of affected
areas; then proceed to
rest of body
• Aim for 10 minutes of
contact time with the skin
• Rinse affected areas last
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