Canine skin conditions can be caused by many different diseases. Symptoms include itchiness, hair loss, bald spots and inflamed skin. The most common causes of canine skin disease are atopy (an allergic response to an environmental allergen), flea allergy dermatitis and food allergies. The skin of a dog can only respond to disease in a limited number of ways. Therefore, many skin diseases look very similar. Specialized testing is necessary to differentiate one skin disease from another and make a definitive diagnosis.
Instructions
Obtain a history from the owner of the dog. Specifically, obtain information about how long the condition has been present and whether the dog has suffered similar conditions in the past and, if so, when. Note what diet the dog is eating and any other medications the dog receives. Find out if the owners have noticed skin lesions on other pets or on human members of the household. Basic information about the dog, such as age, sex and breed should also be recorded.
Perform a physical examination, noting the appearance and locations of the skin lesions. Look for evidence of fleas.
Perform blood testing if systemic disease is suspected based on history and physical examination findings. Blood testing may include a complete blood count, blood chemistries, total T4 values, free T4 by electrodialysis and/or TSH (thyroid stimulating hormone) levels.
Perform a skin scraping by using a scalpel or other sharp object to gently scrape the surface of the skin. Pinch the skin gently before scraping to release any mites from the hair follicles. Place the tissues collected from the skin scraping on a microscope slide with a drop of immersion oil. Examine the slide microscopically for mites. Identify the type of mite, if found.
Perform a skin cytology test by collecting cells from the surface of the skin using a cotton-tipped applicator rolled gently against the skin or tape pressed firmly against the skin surface. Place the sample on a microscope slide and stain the slide with a Diff-Quik type stain. Examine the slide for evidence of bacteria, yeast organisms or blood cells.
Perform a fungal culture by collecting samples of hair and scabs and placing them on a dermatophyte test media (a special type of agar which encourages the growth of fungal organisms and changes color when disease-causing fungi are present). If there is fungal growth with a color change in the test media, samples of the fungus should be collected for identification.
Administer topical flea preventive medication monthly to rule out flea allergy dermatitis. Using selamectin as the monthly topical medication will also help rule out sarcoptic mange. Dogs must be tested for heartworms prior to beginning selamectin. Oral products such as nitenpyram or spinosad may need to be used concurrently in severe flea infestations.
Once skin infections and parasites (fleas and mites) have been eliminated, perform a feeding trial if the dog is still itchy. One diet option for a feeding trial is a novel protein diet containing protein and carbohydrate sources which the dog has never eaten before. Another option for a feeding trial is a hydrolyzed diet in which the protein source has been broken into fragments too small for the immune system to recognize as an allergen. Continue the diet for six to eight weeks, withholding any treats, snacks or flavored medications.
If the dog shows improvement during a feeding trial, ultimate diagnosis of food allergy is obtained by switching back to the original diet and watching for the symptoms to recur. Once the dog is returned to the trial diet, symptoms should resolve again. In reality, if the feeding trial is successful, many pet owners choose to simply continue the trial diet rather than challenge with the original diet.
If diagnosis has still not been reached and the skin condition persists, perform a skin biopsy by removing several small areas of diseased skin surgically and submitting them for biopsy. The biopsy should be interpreted by a dermatopathologist experienced with performing skin biopsies and diagnosing skin disease.
Perform allergy testing and institute hyposensitization therapy. Allergy testing can be done by skin testing (injecting small amounts of potential allergens into the skin and observing for reactions to those allergens) or by blood testing (testing the blood with specific antigens to identify the allergens). Once the testing is completed and the allergens are identified, they can be incoorporated into a hyposensitization program.