Q: My friend’s dog is a 5-year-old Springer spaniel. Recently she developed red, round blotches on her belly. Now, the number of blotches has increased since my friend first spotted them. His dog doesn’t appear to be in any pain, but I have encouraged him to take the dog to his veterinarian. So far, he hasn’t heeded my advice. Am I being an alarmist or could these blotches indicate a serious illness?
A: There are many possible causes for red round blotches on a dog’s skin. To properly treat rashes the first step is to obtain an accurate diagnosis. An important aspect of diagnosing skin disorders is to get a complete history. The type of information that is helpful includes: How long has the rash been present? Is the rash worsening? Has your dog ever had a similar rash and if yes at what time of year? Is your dog itchy? How severe is the itching? Do you have any other pets? Are any of them itchy? How is the general health of your dog? Is your dog currently taking medication? Have any oral or topical medications been tried for this rash? Did they help?
A complete history can give your veterinarian clues to what could be causing the red blotches. Very commonly red lesions that are not itchy can be caused by a bacterial infection (pyoderma). Less likely are fungal infections, commonly referred to as ringworm (dermatohytosis). Allergies can also lead to red blotches but in these cases your dog will be quite itchy.
After taking a thorough history your veterinarian will do a physical examination. The exam will take notice of the type and extent of the lesions. Are they only on the belly or are there other areas of involvement such as the feet or ears? The type of lesion and the locations of the lesions are further clues that are used to arrive at a diagnosis.
There are several common diagnostic tests that are used to diagnose the cause of skin rashes. Skin scrapings are performed by gently scraping the skin with a scalpel blade just until slight bleeding occurs. The material obtained is put onto a glass slide with mineral oil and examined under a microscope. Several types of parasitic mites (demodex, scabies, cheyletiella) can be found by skin scrapings. To diagnose fungal infections hairs are plucked from the lesions and the areas on the edges of the lesions. The hairs are placed onto special medium and then observed for 14 days to see if a fungal organism grows. A third diagnostic test is skin cytology. This can be done by touching clear scotch tape to the lesions or by rubbing a Q-tip on the lesions and then rolling the Q-tip onto a glass slide. The material on the slides is stained and then examined under the microscope. The type of cells identified and the presence or absence of bacteria are used to make a diagnosis.
After a complete examination of your dog and the appropriate diagnostic testing, a veterinarian will be able to prescribe the proper course of treatment.