The most reliable way to diagnose demodectic mange is by taking multiple skin scrapings. Of course, the veterinarian will first get a history from the owner about the dog’s health and symptoms and then will conduct a thorough physical examination. Skin scrapings are just what they sound like: physical scrapings of the areas of patchy hair loss. The veterinarian will squeeze the affected areas to encourage the mites to come out of the hair follicles. He then will use a sharp sterile scalpel blade to scrape fairly deeply into at least 4 or 5 of those sites, to the point of drawing a small bit of blood. The samples of the scrapings will be placed onto glass slides and examined under a microscope. Demodex mites usually can be readily identified through this process. They have a unique shape, size and profile that are easily recognizable microscopically. It is important to examine scrapings from several different locations, because each patchy area may not have the same number of adult mites proliferating at any given time.
In some cases, the veterinarian may recommend taking actual skin biopsies instead of superficial skin scrapings to confirm a diagnosis of demodectic mange. For example, this is commonly done in Shar-Peis, because of their thick, coarse skin. Skin biopsies may also be recommended for dogs whose feet are affected by the mites (this is called pododermatitis).
Adult dogs that present with signs of demodectic mange should also be evaluated for evidence of systemic disease. A systemic illness is one that affects or pertains to the body as a whole, as opposed to one that affects only certain organs, areas or body systems. Typically, the search for systemic disease will involve a urinalysis, routine blood work (a complete blood count and serum biochemistry profile), abdominal and thoracic (chest) radiographs (X-rays) and screening tests for thyroid, endocrine and other metabolic disorders. More advanced testing may also be appropriate.