Sat, 06/11/2022 - 11:01am

Itching for Answers

Everything you need to know about hot spots and allergy testing


What is a hot spot?


The medical terms for hot spots are acute moist dermatitis and pyotraumatic dermatitis. They appear suddenly as areas of swollen, red, oozing skin. These sores arise as a result of the dog biting or scratching at the skin in an attempt to relieve pain and itching.

Historically, the condition was known as “summer eczema,” as many cases occur that time of year. It has also been classified as a surface skin infection. Although bacteria may be found in the lesions, true hot spots are not just skin infections, and they do not clear up with antibiotic therapy alone.

A hot spot takes form rapidly. The area becomes red, swollen, intensely itchy and sometimes oozes blood-tinged fluid. It may start as a small sore and enlarge quickly. I have seen them range in size from one inch in diameter to covering a large dog’s entire head.

Hot spots develop more commonly in long-haired breeds, but not exclusively. The lesions are usually painful, so caution is advised when examining your dog. The affected areas are often near the underlying cause. They often erupt on the side of the face on dogs with ear infections.


What causes hot spots?


The exact etiology, or cause, of acute moist dermatitis is unknown. Anything that can start an itch-scratch cycle may predispose a dog to this condition. The dog is so intensely itchy that the area is traumatized by scratching and biting in a short period of time. Severe hot spots can develop within hours in some dogs.

Most hot spots appear as an allergic reaction. Flea bites, food and environmental allergies are the most common underlying causes. Parasite infestations of the skin, such as scabies and demodex mange mites, can also trigger a reaction. Ear infections, anal-gland impaction and trauma to the skin from grooming may also set things in motion.

The key to preventing hot spots is identifying the cause. An aggressive flea-control program, especially for flea-allergic dogs, will greatly reduce the incidence of dermatitis. Specific treatment of other allergies, parasite infestations or ear infections is necessary to prevent recurrence. Any other situations that initiate the itch-scratch cycle, including anal-gland disease, clipper burn or foreign bodies in the fur, should be treated.


How are hot spots treated?


The reaction causing the hot spot on the skin will keep spreading and enlarging until the fur is removed by clipping and the sore is cleaned. The clipped area should extend slightly past the line of the hot spot. As mentioned previously, hot spots can be painful, so sedation or even general anesthesia may be required to clip and clean.

Next, the lesion should be cleaned with a disinfectant such as betadine or chlorhexidine. Topical medications in the cream or spray form should be applied to keep the lesion dry.

Depending upon the severity of the dermatitis, oral or injectable steroids, such as prednisolone or dexamethasone, can be administered and prescribed. Oral systemic antibiotics are not usually necessary unless a secondary bacterial infection of the skin is present.

The dog may need to wear an Elizabethan collar to stop the cycle of biting and scratching. Once these hot spots are clipped, cleaned and treated, they clear up quickly. Dogs that do not respond to treatment or suffer with recurring hot spots may require more extensive diagnostic tests to determine the underlying cause.


Why does my dog have allergies?


While not usually life-threatening, allergies can be uncomfortable for dogs as well as their owners. Most symptoms are associated with skin problems, but some allergies, if left untreated, can lead to chronic respiratory conditions. Excessive licking and compulsive scratching will cause fur loss and sores on the skin. Dogs with respiratory allergies frequently sneeze and wheeze.

Most allergies develop in the second year of the dog’s life. During the first year, the dog will be exposed to many types of allergens, mostly through contact with the skin. A smaller number of allergies may be caused by food, usually the protein source, and inhalant particles they breathe in.

In the second year of life, the dog’s immune system will overreact to the foreign substances called antigens and initiate the release of immune cells. These, in turn, release inflammatory substances, such as histamine, which produce the symptoms of itching and sneezing. Rarely is a dog allergic to just one thing.

Many allergic dogs are born with a weaker skin barrier, which allows the antigens to penetrate the skin more easily. These dogs also have a poorer immune response because of which secondary bacterial skin infections occur.


How can I find out what my dog is allergic to?


The first step to determining the cause of your dog’s allergies is a thorough physical check-up by your veterinarian. Careful examination of the skin may reveal the presence of external parasites such as fleas and mites. Additional procedures, including skin scrapings and biopsies, help identify other types of infections that may be present.

Once external parasites and infections are ruled out, your veterinarian may recommend testing for specific allergens. Dog allergens fall into several groups: contact allergies, which include many grasses, plants, dust mites and molds; flea allergies, since many dogs are highly allergic to flea bites; food allergies, which are usually a reaction to different types of proteins, and inhalant allergies, which are reactions to allergens in the air that are breathed in through the nose or mouth.

Allergy testing is done either with a blood test or with intradermal testing, which is sometimes also called skin testing. For many dogs, both tests are needed.


What is involved in an intradermal test?


The dog is lightly sedated, and the fur is clipped from an area on the side of the chest. Approximately 60 small injections are given just under the skin, like a “TB test,” If the dog is allergic, a red bump, or “hive,” will form at the site of one or more injections. This type of testing is more traditional, more involved, and more expensive than blood testing, but it also more sensitive and has very few false positive reactions.


What is involved in an allergy blood test?


Allergy blood testing simply involves drawing a blood sample and sending it to a laboratory. The results come back in two to three weeks. This type of testing does not require sedation and is less expensive. It does require careful interpretation, and certain laboratories have more sensitive tests than others.

Neither skin testing nor blood testing is consistently better. For many dogs, the results would be comparable on either test, but for some dogs, either the blood test or skin test provides more information. It is hard to predict in advance which will be best for an individual dog. Overall, the accuracy of these tests is about 75 percent.

Allergy tests evaluate a dog’s reaction to tree, weed and grass pollens, dust components, mold spores and fleas. These are the major allergies of dogs and account for 99 percent of allergy problems. In rare cases, it may be necessary to test for unusual things like allergies to cats, humans or insects.

Tests are available for food allergies, but such tests are unreliable. If food allergies are suspected, the best test is a food-exclusion diet consisting of one or two components for several months.

Certain medications will interfere with allergy testing. Any cortisone pills, ointments, sprays, ear drops or eye drops must be stopped at least two to four weeks before testing. Antihistamine pills must not be taken for at least seven days before testing. Check with your veterinarian to see whether any medications or flea-tick-heartworm products are OK to give before your dog is tested for allergies.



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