Diagnosing Hair Loss and Scratching in Dogs

Dog Scratching
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Skin disease is the most common reason dogs visit the veterinarian, and hair loss and scratching are two of the most common manifestations of canine skin disease. To be able to successfully diagnose and treat your dog for scratching and hair loss, your veterinarian will likely need to perform some basic laboratory testing.

Many different conditions can cause skin disease, but the skin of the dog reacts to disease in a limited number of ways. As a result, many of the diseases that cause skin problems in dogs cause similar symptoms that look identical to one another.

Collecting an Informative History

Your veterinarian will begin the search for the cause of your dog's hair loss by asking you some basic questions. Prepare to answer these questions:

  • When did your dog start to lose hair?
  • Is your dog itchy?
  • Has your dog suffered from similar problems in the past? If so, when?
  • Is your dog currently taking any medications? Herbal supplements?
  • What is your dog eating at meals and in the environment?
  • Have you noticed symptoms other than scratching or hair loss?
  • Are there other pets in your home and, if so, are they experiencing similar problems?
  • Are family members noticing any abnormal skin lesions?

Physical Examination

Your dog will have a physical examination from head to toe, looking for evidence of parasites (such as fleas, ticks, and lice), skin lesions (such as red spots, scabs, sores) and overall health. The examination will include the eyes, ears, teeth and other body parts as well. This is because skin disease can sometimes be a manifestation of disease in an internal organ system or other parts of the body.

The results from the history and physical examination will lead your veterinarian in determining which diseases are most likely causing the hair loss and itching for your dog. The results will also help in determining which diagnostic tests should be performed.

Specific Tests for Skin Disease

If your dog is suffering from skin disease and has been losing hair or scratching, there are several tests your veterinarian may recommend performing. These include:

  • Skin scrapings to look for evidence of the mites that cause mange
  • Skin cytology looking for evidence of yeast and bacterial infections in the skin
  • Fungal cultures that check for ringworm (not a worm) and other fungal infections
  • Skin biopsies if skin cancer or other serious skin disease is suspected

In some cases, if your veterinarian suspects that a more systemic (whole-body) disease is causing your dog's skin disease, a blood screen may be recommended. A blood screen usually consists of a complete blood count (CBC) and a chemistry profile.

The complete blood count looks closely at the red blood cells and white blood cells in a blood sample. The blood chemistry profile allows the evaluation of kidney function, liver enzymes, protein levels, and electrolyte levels. In dogs with skin disease, blood screening may also include tests that evaluate the thyroid function, including total T4, free T4, and/or thyroid-stimulating hormone (TSH).

Diagnosing Skin Disease With Flea Control

If your dog is scratching and losing hair, one of the first things your veterinarian will likely recommend is a reliable form of flea prevention if you are not already using flea control. This is because fleas can be notoriously difficult to find on dogs, even when fleas are the main trigger for the condition. If fleas are not the cause, controlling them is still important, as any fleas are likely to make an original skin problem much worse.

Diagnosing Skin Disease Caused by Food Allergy

After fleas have been treated and ruled out as the cause of the itching, your veterinarian may recommend doing a food trial. A food trial involves feeding your dog a special diet for two months to bring your dog's immune system back to a non-reactive baseline.

This special diet is called a novel protein diet or a hydrolyzed (chemically digested) diet; it is devoid of all protein and carbohydrate ingredients that are the most common triggers of food allergy in dogs. Normal protein triggers are beef, milk products, chicken, and eggs, while common carbohydrate triggers are wheat, corn, and soy.

Once the dog's immune system has calmed down, these ingredients can be tried one by one to see if they induce skin reaction. If so, itching symptoms will appear within about three days. Most food-allergic dogs will show sensitivity to more than one kind of protein or carbohydrate.

Allergy Testing and Immunotherapy (Hyposensitization)

If other causes of hair loss and scratching have been ruled out and if your veterinarian is relatively certain that your dog is suffering from atopy (an immune system that is sensitive to something in your pet's environment), then allergy testing may be recommended.

Allergy testing can determine which substances your dog is allergic to. The treatment for acquired allergy is immunotherapy, also called hyposensitization. This involves injecting a solution of the allergen (the substance causing the allergy) into your pet over a period of time in an attempt to train your pet's body to not respond abnormally to the allergen.