Itching (Pruritus) in Dogs
Pruritus is defined as an unpleasant sensation within the skin that provokes the desire to scratch. Itching is a sign, not a diagnosis or specific disease. The most common causes of itching are parasites, infections, and allergies. There are many skin diseases that do not initially cause itching. Itching may develop because of secondary bacterial or yeast infections. It is possible that by the time itching develops the initial cause is long gone.
A dog with pruritus will excessively scratch, bite, or lick its skin. Itching may be general or confined to one area. Your veterinarian will perform a thorough skin history and physical examination. Parasites, including mites and fleas, are the first possible cause your veterinarian will seek to exclude.
Next, your veterinarian will look for infectious causes of skin disease. Concurrent bacterial and yeast infections are common causes of itching. Infections are often accompanied by hair loss, scaling, odor, and fluid discharge. Excessive scratching of feet and face are common in animals with concurrent yeast and bacterial infections. If such an infection is suspected, your veterinarian will often prescribe a 21- to 30-day course of antibiotics.
If the itching goes away, then the cause was a microbial infection. However, if the dog’s itching is unchanged or only somewhat better, the most likely underlying cause may be an allergy. The most common causes of allergic itching are insect bites, food allergy, and a reaction to allergens in the environment, such as pollens, molds, or dust (see Allergies in Dogs : Airborne Allergies (Atopy)). Sensitivity to insect bites is readily identified. Dogs that have seasonal itching are likely reacting to seasonal allergens. Dogs with year-round allergic itching may have a food allergy. Food allergy is confirmed or excluded based on response to a diet trial (see also Allergies in Dogs : Food Allergies). During a diet trial your dog is fed a diet that does not include the foods it has normally consumed. Your veterinarian will specify a diet, often one containing fish or other meats not previously fed. To help your veterinarian isolate the food allergy, you will need to follow the prescribed diet fully and carefully and avoid providing treats that do not comply with the diet. Allergy testing and intradermal skin testing show only antigen exposure patterns. These tests are used to determine the contents of an immunotherapy vaccine, but are ineffective in identifying food allergy.
Successful treatment depends on identification of the underlying cause. Dogs whose cause of itching cannot be identified, or those in which treatment of the underlying disease does not eliminate the itching, will require medical management. Commonly prescribed anti-itching medications include antihistamines, glucocorticoids, and essential fatty acids.
Treating itchiness with antihistamines is common, but their success in treating itching is highly variable. The most commonly used antihistamines include hydroxyzine hydrochloride, diphenhydramine, amitriptyline hydrochloride, cetirizine, and fexofenadine. A 7- to 10-day thera-peutic trial of any one antihistamine is required to see maximal benefit. Your veterinarian will assess your dog’s condition and prescribe antihistamines if appropriate.
Glucocorticoids are anti-inflammatory steroids. They are often considered the most effective drugs in the management of itching. However, these drugs can cause adverse side effects, including excessive hunger, thirst, and urination. These drugs also suppress the function of the adrenal glands and increase the risk of diabetes and secondary urinary tract infections. Thus, these medications are prescribed only in limited circumstances. The use of glucocorticoids to control itching caused by infections is inappropriate.
Essential fatty acids are rarely effective as sole anti-itch agents; however, they often can be successful when used in combination with antihistamines or steroids because they may enhance the effectiveness of antihistamines or allow a smaller than usual dose of steroids.