Springer, Roxanna. “Itchy Skin – Why? What? Next?” 31.2 (June 2003) : 20-22. A discussion of canine skin problems, their causes, and some treatment suggestions. Skin disorders
Itchy skin (pruritis) is a problem for many dogs, including mixed breeds and wild canids. The associated scratching, rubbing, chewing, or licking is a problem for many dog owners. Why is skin itchy? What do we do about it?
Pruritis indicates inflamed skin from any number of causes such as a grooming injury, a parasitic infestation, or a disease within the dog’s body. Sometimes, the owner or veterinarian doesn’t see the scratching, rubbing, chewing, or licking but only the evidence of self-trauma with missing or matted hair that might hide inflamed or irritated skin. Pruritis has complications such as skin infections (pyoderma), ear infections, hot spots, and conjunctivitis. Teeth can be worn down because of excessive chewing.
Canine skin is thinner and more sensitive to damage than is human skin. Intact, healthy skin is the ultimate barrier against infections. When the skin surface is broken (easily in the armpits and groin), any problem quickly increases in size and seriousness. Multiple causes can be unrelated and only discovered during treatment for known causes. For example, acral lick dermatitis, commonly known as lick granuloma, has many causes (e.g., al ergies, arthritis, skin tumors, inflamed nerves, fungal infections, ectoparasites, and psychological factors like boredom or stress).
There are four etiologiesofpruritis: parasitic, al ergic, bacterial/fungal, and other (e.g., seborrhea and autoimmune/immune-mediated diseases). Severe itching -- constant, keeps the dog and owner awake -- suggests atopy, scabies (highly contagious), fleas (the most common cause), food al ergies, or a cutaneous yeast infection. These might be gradual or show up suddenly. Diagnostics include skin scrapes, fungal parasite cultures, and skin tests. Skin biopsy is used when an immunological disease is suspected or when other symptoms and history are unusual. Parasites causing pruritis include fleas (the leading cause) and ticks, maggots/grubs, and mites. Scabies (caused by sarcoptic mange mites) diagnosis is difficult with skin scrapes often negative. Sometimes, a scabicidal therapy of lime sulfur or ivermectin must rule out this cause. Pruritic allergies have six types: parasitic (e.g., reactions to bug saliva), atopic, food, contact, drug, and ‘bacterial hypersensitivity.’ Diagnostics for al ergies include skin and blood tests or hypoal ergenic dietary trials. Intradermal skin tests are similar to al ergy tests used for humans, al owing identification of individual al ergens and measurement of their strength in immunoglobulins (e.g., IgG, IgM, IgE). Blood testing is a newer procedure, sometimes not measuring certain immunoglobulins and not identifying specific al ergens. Al tests have their weaknesses (e.g., subjectivity, influence by other treatments, sedation).
A much bigger problem than discomfort from the flea bites, however, is al ergy to fleas – about 14% of dogs are so affected. With convenient and effective methods of flea control, this problem should diminish in frequency.
Atopy is the next most common al ergic dermatitis -- affecting about 10% of dogs. Usual y showing up when a dog is one to three years old, atopic dermatitis is an inherited tendency to develop IgE antibodies in response to seasonal al ergens inhaled or absorbed through the skin. Diagnosis can be difficult because most dogs with atopy are also al ergic to fleas. Sometimes, the only manifestation of atopy is ear canal infection. Skin scraping, bacterial and fungal cultures, and hypoal ergenic test diet precede complex and expensive intradermal skin testing or blood testing for atopy.
Food al ergy is the third most common cause of al ergic pruritis, occurring at any age and in any season. Current thinking is that ‘adverse food reaction’ might be a better description of the condition, with itchy skin perhaps the most frequent symptom. Hypoal ergenic diet trial is the best method to determine food al ergies and requires strict adherence to specific limited and novel ingredients for several months. The original diet should also reintroduce to assure that any improvement is due to the food change and not
simply chance. Many dogs having food al ergies may also have atopy, making diagnosis and treatment difficult.
Contact dermatitis al ergies are sensitizations and delayed reactions to chemicals or other irritants found in many substances (e.g., soaps/shampoos, flea col ars, wool/synthetics/leather, plastic/rubber dishes, grasses/pol ens). Common irritation contact dermatitis causes itchiness and inflammation only at the site of contact, while less common al ergic contact dermatitis rashes can spread beyond the contact area. Also, whereas only one exposure can cause irritation dermatitis, multiple or constant exposures to al ergens are necessary to cause al ergic contact dermatitis.
Drug al ergy and bacterial hypersensitivity are rare.
Ringworm fungal infection itself is not an itchy skin condition, but secondary bacterial skin infections can occur in scabs that provoke licking and scratching. Other causes of pruritis include primary and secondary seborrhea and autoimmune and immune- mediated diseases. Primary seborrhea is incurable, so secondary seborrhea should be ruled out first. Autoimmune diseases (e.g., pemphigus) involve autoantibodies attacking normal skin cel cohesiveness. Immune-mediated skin diseases (e.g., lupus erythematosus) are systemic attacking the skin as wel as other locations including kidneys. With many symptoms and causes, there are also many treatments, especial y after 25 years of veterinary dermatology. Associated skin inflammations must be treated first to reduce the scratching threshold. Essential fatty acid fish products help as do a variety of shampoos that rehydrate skin, treat bacterial infection, and control seborrhea. Antihistamines provide itch relief for 20-40% of atopic dogs. Dogs not responsive to these treatments are treated with immunotherapy injections of solutions specifical y designed for the individual dog ‘s particular al ergens and their representative effects on the dog. Injections taper off in frequency when hyposensitization begins taking effect.
Treatment success depends on accurate, timely, and complete reporting by the dog’s owner on symptoms and recent changes or events in the dog’s environment. Fol ow-up monitoring is essential as eradication or control of one etiology might not affect others. Also, there are complications to note with some treatments, especial y with long-term steroid use.
The 5 Minute Veterinary Consult (Til ey& Smith, copyright 1997), pp.134-5
Dog Owner’s Home Veterinary Handbook (Giffin & Carlson, 2000), Chapter 4 The Skin and Coat
“Adverse Food Reactions,” by Manette Kholer, DVM, DogWorld, June 2003, p.14
Animal Dermatology Clinic of San Diego (www.animaldermatologysd.com)
http://www.tatescreekanimalhospital.com/senior_pets.htm#SKIN%20AND%20COAT%20CARE%20FOR%20SENIOR%20PETS
Special thanks to Kirk Feinberg, DVM for his help with this article and care of our dogs over the years.
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