"Scratch that itch" - A Seminar organised by the SNC
Dr. Neil McEwan, MRCVS
The Southern Newfoundland Club held
a seminar on 05 February 2011 focused on skin conditions. The speaker was Dr. Neil McEwan, MRCVS who is the Senior Lecturer in Veterinary Dermatology at Liverpool University. He also works as part of
a small team at a purpose-built small animal teaching hospital specialising in skin conditions. His work consists of referral work, teaching students and some research (largely clinical research). The
following is a summary of his presentation prepared by Pippa Woodward-Smith.
Skin conditions are very common in small animals and exceptionally common in dogs with 25% of the cases presenting at vets surgeries relating to skin related conditions, ear infections or anal glands
disease, in comparison with 10Ė12% relating to dermatological conditions in people and 6Ė8% in cats.
When presented with chronic skin conditions, how do they diagnose the cause? There are several ways but mostly they use two methods: 1) "Aunt Mimi" and 2) "Find the pony".
"Aunt Mimi" was a reference to an aunt who wore particularly distinctive outfits! In a similar way some conditions are easily identified by pattern recognition of clinical signs, history and
results of diagnostic tests. Others require carrying out a lot of clinical tests to arrive at a diagnosis by sifting through all the information collated from the tests and ruling out certain conditions
(hence "Find the pony") which can take a long time.
An important question in diagnosis is to determine if the skin condition is caused by a contagious parasite, such as fleas, sarcoptes, or cheyletiella, or a contagious infection such as ringworm. Contagious
skin conditions can affect other dogs in the household or even people.
The physical examination of the animal will start at the front of the animal and work to the back documenting the distribution, type of lesions and whether there is any symmetry or pattern to the lesions.
There are two types of lesions recorded: primary skin lesions, such as pustules or hot spots and secondary lesions such as ulceration or skin erosion (often caused by autoimmune disease). Other common
secondary lesions in skin conditions include alopecia (loss of fur), comedones (black heads which often indicate dermodectic mange i.e. mites) and whiteheads on pustules (often a bacterial infection).
Secondary bacterial infections are very common with skin conditions. The cause of many skin problems is often an allergy that leads to secondary bacterial infections. The most common skin problems in
dogs (in order) are:
- Infections - Staphylococcus or Malassezia (yeast)
- Endocrine (hormonal)
- Neoplastic (skin tumours)
Interestingly, the most common skin problems in cats are similar but they are not as prone to secondary infections as dogs. They also donít tend to suffer
from endocrine skin problems.
Canine Atopic Dermatitis
The most common cause of skin complaint is canine atopic dermatitis, which is diagnosed in 60% of the cases seen by Dr McEwan. It is usually chronic and not curable. This is a genetically predisposed
inflammatory and pruritic allergic skin disease with characteristic clinical features. Interestingly it is very similar to the same condition in humans. It is commonly associated with antibodies being
produced in response to environmental allergens. The genetic predisposition of the disease is extremely complex and there are probably several genes involved, but this research is in its early days.
There is no test to diagnose this condition diagnosis depends on excluding other causes of itch. Therefore diagnosis and investigation includes looking at history e.g. where is the itch, distribution
of the lesions, age of onset, whether it is chronic, whether it is seasonal? Skin conditions typically first present between 6 months to 3 years of age and often affects the feet, ears and undercarriage.
Interestingly, conditions are usually symmetrical e.g. all feet or both back feet.
As the underlying cause is often allergies, allergy testing of the blood and skin can be useful. Skin tests involve an injection of a small amount of various likely allergens (diluted) under the dermis
to test for a reaction, being a raised red spot. To establish what is a positive reaction for that individual two control injections are carried out: one a positive control with a histamine which should
cause an allergic reaction in all individuals and a second control using saline which should not cause a reaction.
Allergies for this condition tend to be mites, mould or house dust. Allergy tests are not good at establishing a diagnosis as you can get both false positive and false negative tests i.e. if you get a
positive reaction you can say this is consistent with an allergy but it is not a definitive test and likewise a negative reaction does not rule out atopic dermatitis. This is carried out in conjunction
with all other tests.
Treatment of canine atopic dermatitis is a lifelong plan. No single treatment works in every case, there is usually more than one treatment. Steroids can work well but is not used as a long term treatment
due to side effects. The lifelong plan covers a number of areas: treating the allergy with avoidance of the allergen, immunotherapy (which helps to desensitise the individual to the allergen), use of
anti-inflammatory medication and correct diet; supporting the skin function by the use of special shampoos and essential fatty acids in the diet; and control of secondary infections and flare factors
i.e. bacteria, yeast and parasites.
Pyotraumatic dermatitis (hot spots)
A skin condition many Newfoundland owners are familiar with is Pyotraumatic dermatitis, aka, hotspots or acute moist dermatitis. This is a common problem which can spread very quickly, particularly with
dense coated breeds. There are a number of factors that influence this condition:
- initiating factors - parasites, allergies, otitis and anal sac infections;
- compounding infections - a dense coat, hot weather and humidity;
- secondary bacterial infections; and
- self trauma - scratch, nibble and lick at the area.
Treatment involves clipping of hair around the affected area, remove debris and exudate, prescribe glucocorticoids if very painful, prescribe antibiotics and identify and treat the initiating factor.
Interestingly, there does not seem to be a link with skin conditions to hormones (although hormones will influence the skin). Although stress can make an existing itch problem more itchy it isnít often
a cause. An exception is a similar condition of lick granulomas which are primary lesions similar to hot spots located on the anterior portion at the top of the front or back feet, which does seem to
be associated with stress/boredom.
Otitis is the term given to problems associated with he outer, middle or inner ear. There are a number of factors that influence this condition:
- primary factors - e.g. grass seeds or occasionally food;
- predisposing factors - physiological differences found in particular breeds e.g. Sharpeis have narrow ear canals and environmental/life factors such as swimming; and
- perpetuating factors - infections that stop the problem being resolved e.g. bacterial or yeast infections.
Chronic otitis can cause pathological changes in the ear canal such as calcification of the ear cartilage - which causes the soft cartilage to become bony. Often serious cases of otitis can be cleared
using a high tech ear wash with a scope device that both removes detritus in the ear canal and washes through with saline solution to remove the infection. With chronic otitis where pathological changes
have occurred then it can need more intensive investigations e.g. radiographs or CT scans. If there is a history of chronic ear problems then put them on maintenance regime cleaning once/twice a week.
Dr. McEwan recommended home ear cleaning with one of the various products available in pet shops, simple lavage and massage, to treat and prevent problems. In dogs with no obvious signs of ear problems,
however, he did not recommend regular cleaning.
The presentation finished with some graphic, video footage of cleaning cats and dogs ear canals, although this did not seem to put anyone off the excellent lunch that followed!