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Hot spots on your pet: what's the skinny?
"Hot spots" is one of the most commonly used layman's terms in veterinary medicine. What does this term mean and what is its origin? Ironically, there is a consensus amongst the veterinary community as to what hot spots refer to, however there is no consensus as to where the term originated.
Hot spots, also known as pyotraumatic dermatitis or acute moist dermatitis, refers to rashes that pop up suddenly on the top layers of an animal's skin. By suddenly, I mean within hours. These rashes resemble a human eczema-type condition as the rash begins to weep. The animals affected appear to have been burned, the areas become very warm to the touch, and are more common in the warmer months. For these reasons the term hot spot is very appropriate.
What leads to hot spots? These painful rashes are usually the result of some allergy or irritation such as a bug bite (including fleas and ticks), contact irritation, a seasonal allergy or a food allergy. Rather than developing a generalized rash, the areas are very focal. The most common sites for hot spots are around the neck and ears, followed closely by the thigh and tail regions. As a matter of fact, it was thought that all dogs with hot spots had underlying ear infections. Therefore, if the ears were infected then the dog would start scratching at that area leading to these types of rashes. A recent study statistically proved not all dogs with hot spots had ear infections as well.
What causes a regular rash to turn into a hot spot? There is a bacteria named Staphylococcus intermedius that releases an exfoliative toxin. An exfoliative toxin refers to a toxin produced by the bacteria that causes the cells of the skin to exfoliate, or fall off (like foliage falling off a tree). The dead skin cells, bacteria and fluid from inflammation make a gooey mess.
Now, don't worry. This particular type of staphylococcus, or "staph" for short, is not an antibiotic-resistant type of bacteria. Staph intermedius is considered normal flora. Normal flora refers to small numbers of bacteria that live on our pet's body at all times and normally do not cause a problem because they are kept in check by the immune system. S. intermedius is one of those bacteria. However, S. intermedius can also be a bit of a naughty bacteria with the right conditions. I like to use the analogy of a sixth grade class and a substitute teacher. If the regular teacher is forced to call in sick on short notice, the students don't change but the situation does, and these normally angelic students may try to take advantage of the situation. Well, that is the same scenario in this situation. Something (usually an allergy or irritation) temporarily compromises the immune system only at the top layer of the skin. Once compromised these "angelic" bacteria immediately recognize this change and take advantage of the situation. They not only proliferate like crazy, but also produce a toxin that turns a minor itch into a disgusting, weeping eczema. This weeping rash is also very itchy, and just like anyone with an itchy rash these dogs are going to scratch it. Unfortunately, the more they scratch the worse it gets, so within a very short period of time the pet turns this into truly a "bloody mess" matted with hair.
How do we treat hot spots? Similarly to the substitute teacher who is feeling a bit overwhelmed by the boisterous class, we call the principal to settle the students down. Although hot spots can be treated with topical medicated ointments it can be difficult (if not impossible) to apply these medications because the rash is so painful. Therefore, we veterinarians will many times use systemic antibiotics with or without cortisone to get this under control.
Once we get the rash under control it is time to figure out what caused it. If the rash is an isolated incident once or twice a year, then just treating it is sufficient. However, if the rash comes back as soon as the medications are finished, it is important to let your veterinarian know. This is not a failure of the medication, but rather time to try to diagnose and treat the underlying cause of the inflammation.
Dr. Kearns is a veterinarian with a special interest in emergency and critical care. He has been in practice for eight years. Dr. Kearns is pictured here with his son Matthew and his cat, The One Eyed Guy.