Anyone who has seen a cat constantly scratching or chewing on itself probably has seen a cat with skin allergies, which medically are referred to as “atopy” or “atopic dermatitis.” Whether caused by exposure to plants or pollens, flea or other insect bites or ingredients in food, skin allergies can cause mild irritation to dramatic sores from self-trauma and resulting secondary infections. The precise cause of feline skin allergies is difficult, but usually not impossible, to diagnose. Veterinarians have several tools at their disposal to assist them. These include observation of the cat’s symptoms (especially whether they are seasonal), assessment of its response to treatment, standard blood work and elimination of other possible causes of the clinical signs. If an immune-mediated hypersensitivity reaction is suspected but confirmation remains difficult, a “patch test” series may be performed.
Diagnosis Based on Clinical Signs
Skin allergies in cats cause classic clinical signs, usually intense itchiness (pruritis). Many veterinarians are comfortable making a presumptive diagnosis of skin allergies based upon the cat’s clinical presentation. If treatments to alleviate the cat’s symptoms are administered and the problem resolves, no further tests should be necessary. For example, if a flea-infested cat is scratching vigorously to the point of self-trauma and the scratching goes away with appropriate topical and environmental treatment, it is reasonable to assume that the condition was caused by flea-bite hypersensitivity. Similarly, if a pruritic cat stops scratching with a change in the owner’s laundry detergent, it is reasonable to consider that the prior detergent was the offending allergen.
Most veterinarians presented with a severely itchy cat will take a complete history and conduct a thorough physical examination, looking especially for evidence of external parasites, bacteria and/or yeast. They may take skin scrapings, examine plucked hairs microscopically and look closely at a number of samples taken from the ears and elsewhere on the cat’s skin. Fungal cultures may or may not be appropriate.
Testing for Skin Allergies
A standard complete blood count, serum chemistry panel and a urinalysis are often used to screen for possible underlying medical conditions that could be causing or contributing to the cat’s clinical signs. In atopic cats, unlike in dogs, the blood work often discloses a condition called “eosinophilia,” which your veterinarian can discuss with you if necessary. Other laboratory tests also are available, including measurement of serum antibodies to particular allergens and an intradermal “patch test.” The skin patch test involves injection of tiny amounts of a number of different allergens into the cat’s skin, and observing and measuring the skin reaction (called a “wheal”), if any, to those distinct allergens. Skin biopsies can be taken to help rule out other causes of clinical signs as well, although biopsies will not reveal allergic causes.
If food allergies are suspected (they are fairly common in our companion animals and are especially probable if the cat’s signs are nonseasonal), your veterinarian may recommend an elimination diet. In a nutshell, this means putting the cat on a bland diet with few ingredients (often rice and chicken), observing the cat’s skin reaction, if any, to the food, and then gradually adding in other foods to assess how the cat reacts to them. This process can take many months, but if the cat is found to be allergic to certain food ingredients, the time is well spent.