The topic of allergies is very complicated, with multifaceted conditions difficult to diagnose, and are a major frustration for the client and veterinary staff.  The major symptom in all cases is pruritus (itchy) skin. The patient exhibits scratching, rubbing, licking, and/or chewing. Additional symptoms such as:  inflammation, self-trauma, hair loss, lesions and/or skin changes, may also be present.  The areas affected could include the muzzle, ears, flanks, groin, forelegs, or feet.

The initial focus of any itchy patient is to determine the underlying causes of the pruritus.  It is only after all other causes have been excluded that the veterinarian can determine that the condition is due to an allergic reation. Other causes of skin infection and itchy skin can include:

The first step in the diagnosis is to obtain a detailed history of the animal. The history should include previous health conditions, eating habits, dietary history of all things ingested (food, treats, human food, medicaions, supplements), activity level, and areas where the activities take place as well as noting other pets in the household.

Secondly, a thorough physical exam is required.  During the course of this exam, the veterinarian may choose to run certain tests based on the findings during the physical exam. The tests could include skin scrapings, bacterial and/or fungal cultures, and blood work.  If another disease process is suspected, further testing and follow up would be appropriate.  If an underlying cause is found then the pet will be treated appropriately.  The patient will undergo anti-inflammaory and/or antimicrobial therapy to decrease inflammation and manage secondary infections. To control self-trauma, an antihistamine or oatmeal based shampoo my be prescribed.  Devices such as e-collars, t-shirts, and socks or booties may be advised to prevent further self-trauma.  

Flea Allergies - In cases of flea allergy, the paitent is reactive to saliva of the flea. Pruritus is localized to the area of the flea bite(s) and generally ear disease is not present. Treatment consists of treating the patient and its environment for fleas. All pets in contact with the patient must undergo treatment to eradicate the burden of fleas in its environment.

Atopic Dermatitis - This is inflammation of the skin cause by sensitivity to allergens in the environment.  This dermatitis may have a seasonal or genetic component (breed may be genetically predisposed to sensitivities). Atopic dermatitis presents itself with pruritus, recurrent bacterial (ie. staphylococcal), or yeast dermatisis (ie. malassezia), and in dogs specifically, ear infections (otits externa).  Otitis externa is rarely seen in cats. In some cases, cats may exhibit asthma-like respiratory tract disease. Dust mites, pollens, mould spores, danders, and insects are the most common sensitivities. Treatment may consist of one or more of the following:  anti-inflammatory therapy, antimicrobial therapy, allergen avoidance, and/or Allergen Specific Immunotherapy (ASIT). Anti-inflammatory and/or antimicrobial therapy can be prescribed to keep the animal comfortable during episodes or to control flare-ups. An attempt should be made to determine the triggering allergen. If there is no known underlying cause and the dermatitis is year round, a food trial should be considered. Allergy testing should only be carried out after all other causes have been ruled out.  Allergy testing is best performed when the allergy load is highest and prior to any medication therapy.  Once the allergen(s) has been determined, ASIT can be administered.  This is a process of administering gradually increasing quantities of an allergen extract in order to desensitize the patient to the offending allergen(s). One-third of the patients given ASIT have an excellent response, while 1/3 have a good response, and 1/3 have a poor, or no response, to the therapy.

Food Allergy - This is a non-seasonal inflammation of the skin caused by sensitivity to allergens in food.  Adverse food reactions can develop over time.  The patient becomes sensitive to a specific protein, or food additive, in the diet.  The pruritus is distributed similar to that of atopic dermatitis and these two diseases are clinically indistinguishable if symptoms are non-seasonal.  Once all other underlying causes for pruritis are ruled out, and anti-bacterial and antimircrobial therapy has cleared the inflammation, the pet is put on a food trial.  A diet with a novel protein is selected and must be fed for 6 to 8 weeks.  there must be strict adherence to the diet - no other foods, treats, supplements, etc. can be fed during the trial.  The client is advised to keep a diary to record the food fed and symptoms present. If truly a food allergy, improvement may be seen as early as two weeks into the trial.  If at the end of the trial, there is significant improvement, the patient is reintroduced to the previous diet.  Re-occurrence of symptoms is definitive of food allergy.  If there is only a partial improvement, a second trial with another novel protein diet may be warranted. If no improvement with the diet trial, then a food allergy is ruled out.

Further Notes: