Furunculosis in dogs is the medical term for a painful inflammation and infection of the deep layers of the skin surrounding the hair follicles. To give you a better idea of what this means for your pup, integrative veterinarian Dr. Julie Buzby explains the causes, symptoms, diagnosis, treatment, and prognosis for three common types of furunculosis.
Most dog parents are familiar with the occasional hot spot, pyoderma in dogs, dog paw yeast infection, or other dog skin issues. The good news is that the majority of these lesions (i.e. abnormal areas) are very superficial in nature. Plus, they typically resolve quickly and easily.
However, some skin lesions can end up being deep bacterial infections that take several weeks to fully clear up. If your dog develops one of these infections, a veterinarian might diagnose him or her with a funny-sounding condition called furunculosis.
What is furunculosis in dogs?
Furunculosis is a deep infection or inflammation of the skin. It occurs in the portion of the skin below the surface and affects the area around the hair follicles as well as the follicles themselves.
As the name may imply, hair follicles are very small pores located within the skin that hair grows out of. When the follicles become infected or inflamed, the contents tend to move outward. The end result is a furuncle, which is a boil or abscess-like lesion that originates from the hair follicle. The term “furunculosis” describes a condition where the dog has furuncles.
What are the types of furunculosis in dogs?
In order to discuss the intricacies of furunculosis, it is easiest to classify it into types based on the location where it occurs. Three common places for furunculosis in dogs are:
- Paws (i.e. interdigital furunculosis)
- Anus (i.e. anal furunculosis or perianal fistulas)
- Along a dog’s back (i.e. post-grooming furunculosis)
That’s not to say that you won’t occasionally see furunculosis on a dog’s chin, nose, chest, or other places. For example, some dogs might have muzzle folliculitis and furunculosis in dogs (i.e. chin acne). This is most common in short-coated young dogs and consists of multiple small red bumps on the chin and lips.
Or a dog might have eosinophilic furunculosis in dogs, which tends to occur in response to an allergic reaction to an insect bite. Those dogs often have ulcerated areas of the skin or bumps that appear quickly around the face and muzzle. Eosinophillic furunculosis treatment for dogs typically involves steroids and possibly antibiotics if there is secondary infection.
However, those types of furunculosis are less common, so our discussion will focus on furunculosis of the paws, anus, and back.
1. Interdigital furunculosis in dogs
Interdigital furunculosis is also known as pododermatitis, podofurunculosis, pedal furunculosis, or interdigital cysts. As the name might imply, it tends to affect the interdigital region, which is the area between the toes.
Most dogs tend to have hair of some length between their toes. When the interdigital hair follicles become irritated or traumatized, the resulting inflammation causes the follicles to dilate. Then the skin itself begins to appear swollen or cyst-like. Even if the inflammation starts out underneath the paw, it tends to migrate to the paw’s upper surface.
Causes and predisposing factors
There are a variety of reasons that certain dogs may be more likely to develop interdigital furunculosis:
Dogs with shorter hair coats such Basset Hounds, Bulldogs, Bull Terriers, Boxers, Great Danes, Mastiffs, and Staffordshire Terriers as are more likely to develop interdigital furunculosis. This makes sense because longer haircoats may be more protective against elements that could irritate the paws. Plus, short bristly hairs tend to be more irritating to the space between the toes.
Dogs with wider paws and a larger distance in between the pads on the paws are more likely to experience interdigital furunculosis. This is because the delicate furred skin between the toes is more likely to contact the ground or rough surfaces when the pup goes to take a step. Large breed dogs like Labrador Retrievers and German Shepherd Dogs can experience this, as can certain small breed dogs like the Pekingese.
Several other factors can also influence the development of interdigital furunculosis in dogs:
- Body weight—interdigital furunculosis is more common in overweight and obese dogs or those who are bearing weight abnormally on a paw
- Excessive paw licking—a dog’s itchy paws may be due to allergies, anxiety, or other factors
- Foreign bodies such as sharp objects or plant material (e.g. foxtails in dogs).
- Parasites such as demodex (the cause of demodectic mange) and hookworms
- Endocrine diseases like hypothyroidism in dogs and Cushing’s disease in dogs
- Fungal or bacterial infections (commonly isolated bacteria include Staphylococcus pseudintermedius and Staphylococcus epidermidis)
Symptoms of interdigital furunculosis in dogs
A combination of these factors can lead to inflammation of the interdigital region and eventually furunculosis. Initially the dog may start out with mild redness (i.e. erythema) in between the toes. The inflammation may gradually intensify and causes the skin to become swollen (i.e. edematous). Pustules and focal nodules that look like little bumps can also appear.
If there is foreign material in the paw, you may notice a bleeding or draining tract where the object pierced the skin. Bacterial furunculosis in dogs can also be a “smelly” condition. Some owners may notice a foul odor around their dog’s paws.
Your pup may also experience itchiness or pain and will try to lick his or her paws frequently. Over time, the chronic irritation from licking and the inflammatory process can lead to thickening of the skin (i.e. lichenification). These changes can make it more difficult to treat secondary bacterial or fungal infections.
If you notice any of these symptoms, it is best to schedule an appointment with your vet. The sooner you can get to the bottom of the issue, the sooner your dog can get some relief.
Diagnosis of interdigital furunculosis in dogs
The vet will carefully examine your dog from head to toe, with a special focus on your dog’s paws. Most of the time, the vet ends up basing the diagnosis of interdigital furunculosis on your dog’s medical history and clinical signs. The vet may also use special skin diagnostics such as skin scrape testing and skin cytology. These tests are a great way to look for bacteria, yeast, inflammatory cells, or parasites like demodectic mange.
If your vet suspects your dog has an underlying endocrine disorder, he or she may want to perform a few specific blood and urine tests. Also, sometimes a dog doesn’t respond to the first line treatments. In those cases, the vet may recommend bacterial cultures and skin punch biopsies to get more information about what is going on.
Interdigital furunculosis in dogs treatment
For furunculosis of a dog’s paw, treatment involves administering systemic antibiotics for up to 12 weeks. Plus, the vet may recommend using the following treatments:
- Medicated shampoos, ointments, sprays, and leave-on mousse products for topical therapy
- Foot soaks as home treatment for interdigital furunculosis in dogs
- Omega-3 fatty acids for dogs for their natural anti-inflammatory properties
- Topical products that contain ceramides and phytosphingosine to help replenish a diseased skin barrier
- Newer allergy medicine for dogs such as Apoquel and Cytopoint, which tend to have fewer side effects than steroid medications
- Prednisone for dogs, or other steroids to alleviate intense inflammation and pain in more severe cases
- PawZ dog boots to protect the paws from further exposure to the elements when going outside (then promptly remove them)—ask your vet if they are right for your dog as putting them on inflamed feet may be more painful than helpful for your dog
- Surgical intervention in severely affected dogs.
With appropriate treatment, the prognosis for dogs with interdigital furunculosis is good. Also, it is unlikely for furunculosis in dogs to be contagious, so you don’t have to worry about your dog passing it to his or her friends.
While the outlook is positive, I do have to warn you that it is still important to follow your vet’s treatment directions. I know that especially if you have a dog who won’t take pills, it can be tempting to stop giving the antibiotics once it seems like your dog is back to normal. However, it is important to treat most dogs for a week or two beyond the resolution of clinical signs.
Infections that coincide with interdigital furunculosis can be very deep. If you stop the treatment before the infection is completely gone, it may come back. Also, stopping antibiotics too soon can promote bacterial resistance.
Another furunculosis treatment tip is to work with your veterinarian to figure out if the underlying cause is something treatable or preventable. For example, managing a dog’s allergies or anxiety may help reduce future episodes of interdigital furunculosis. Or controlling an endocrine disease can restore your dog’s skin health.
#2: Anal furunculosis in dogs
Furunculosis can also develop around a dog’s anus and perianal regions. This is sometimes also referred to as a perianal fistula or perianal furunculosis in dogs. Unlike interdigital furunculosis, anal furunculosis tends to be a chronic inflammatory disease that usually requires repeat therapies, if not lifelong treatment.
Causes and predisposing factors
The true cause of anal furunculosis in dogs is unknown. However, most veterinary experts feel that it is an immune-mediated disease. In other words, the dog’s immune system begins to attack the skin around the anus. There may also be a link between chronic colitis (i.e. inflammation of the colon) and perianal fistulas in German Shepherds.
Anal furunculosis primarily affects middle-aged dogs, and it may be hormonally influenced because it seems to occur more in intact male dogs. German Shepherd dogs appear to be the most commonly affected dog breed. Other affected breeds include the Australian Shepherd, Beagle, Bulldog, Labrador Retriever, Old English Sheepdog, and Staffordshire Terrier.
Symptoms of anal furunculosis in dogs
Unfortunately, the trouble with anal furunculosis is that initial signs can be difficult to detect. This is especially the case in dogs with longer fur in the perianal areas like German Shepherds. Some dog parents may not notice any clinical signs until they see their canine companion scooting his or her hind end across the floor or notice their dog licking the base of the tail repeatedly. Since it is a painful condition, some pups will carry their tails very low or tucked under their bodies.
When looking underneath your dog’s tail, you may observe a small hole or draining tract coming from your dog’s anus, or immediately next to it. Other clinical signs associated with anal furunculosis include the following:
- Straining to defecate (i.e. tenesmus)
- Painful defecation (i.e. dyschezia)
- Bleeding from the anus or bright red blood in the stool (i.e. hematochezia)
- Smelly or pus-like discharge from or around the anus
- Diarrhea or constipation
- Weight loss
- A lethargic dog
If you see these signs, please contact your veterinarian. Because perianal furunculosis can sometimes be confused with a ruptured anal gland or an anal gland abscess, a full clinical examination with your veterinarian is important.
Diagnosis of anal furunculosis
The vet will start by closely examining your dog and finding out a bit more about your dog’s history. This, plus the appearance of the lesions, may give your vet a pretty good idea that the diagnosis is anal furunculosis. However, in order to rule out other potential causes of these symptoms, (e.g. anal gland abscess, food allergy, or a tumor), your vet may recommend:
- A thorough examination with sedation on board. This is helpful because anal furunculosis can be extremely painful, making it difficult (and unfair to the dog) to try to examine the area in an awake dog.
- Skin cytology and culture testing to look for evidence of a secondary infection.
- Biopsy testing to help cross cancer off the problem list.
- General urine and blood testing to rule out infection elsewhere in the body since treatment often involves the use of immunosuppressive medications.
Anal furunculosis treatment in dogs
After reaching a diagnosis of anal furunculosis, the vet will discuss the next steps. The good news is that despite having an unknown cause, many dogs with perianal fistulas respond well to immunosuppressive medications. In the initial phase of treatment, the veterinarian will prescribe a higher dose of the medication until clinical signs resolve. This can take about four months in some cases, but maybe sooner in milder cases.
After the initial treatment phase, the vet will switch your dog to a lower dose of medication for maintenance purposes. Since 33 to 50% of cases recur after finishing treatment, your veterinarian may recommend continuing the maintenance dose of therapy for the life of the dog.
Oral immunosuppressive medications like cyclosporine tend to be the most effective treatment. In some cases, the vet may recommend using topical tacrolimus (another immunosuppressive medication) in conjunction with cyclosporine. And occasionally in mild anal furunculosis cases, topical tacrolimus can be a stand-alone treatment.
As a word of warning, these immunosuppressive medications can also suppress a human’s immune system. It is important to handle them with gloves and then wash your hands after treating your dog.
In addition to immunosuppressives, dogs with anal furunculosis may also benefit from:
- Pain medications to reduce pain and inflammation
- Fiber supplements to ease defecation
- Special diets to manage food allergies
- Surgical intervention as a last resort—it carries the risk of many complications, including anal strictures and fecal incontinence
Prognosis for dogs with anal furunculosis
Although there are good treatment options, ultimately, there is no cure for anal furunculosis in dogs. But the prognosis for these pups is still good when it comes to managing their clinical signs. Thankfully, most cases will start to show some inkling of improvement within the first couple of weeks.
Since many of these dogs require life-long (or at least long-term) medications, regular follow-ups with your vet are important. These appointments allow your vet to ensure the medications are working correctly and make any needed adjustments.
#3: Post-grooming furunculosis in dogs
Unlike interdigital furunculosis and anal furunculosis which had a variety of contributing factors or an unknown cause, post-grooming furunculosis has one distinct trigger—grooming. Post-grooming furunculosis is a skin disease of dogs which, like the name indicates, usually occurs in the first 24 to 48 hours after a grooming.
Causes and predisposing factors
During grooming, the skin or hair follicle may be traumatized or irritated by vigorous scrubbing and/or brushing the fur in a backwards direction. This is problematic because it causes small defects in the skin’s barrier. Normally healthy skin does a great job of keeping bacteria from invading. But when the skin barrier breaks down, bacteria have free access to the hair follicles and deeper layers of the skin.
To further complicate matters, the disease-causing bacteria Pseudomonas aeruginosa can exist in wet environments. Bottles of soap and shampoo or damp grooming tools are the perfect places for it to thrive. Plus, Pseudomonas has special enzymes that help it attach to skin and evade the body’s defenses. This makes these infections difficult to treat.
The combination of a broken down skin barrier and exposure to contaminated grooming products or tools can lead to post-grooming furunculosis.
As you can imagine, this could potentially happen in any age, breed, or gender of dog. More studies indicate that short-coated breeds tend to be prone to developing post-grooming furunculosis. However, one study observed that was most common in Labrador Retrievers and German Shepherd dogs, and another showed it was more common in dogs with medium or long haircoats. So the verdict is still out.
Symptoms of post-grooming furunculosis
As you can see from the picture below of post-grooming furunculosis, most affected dogs have skin lesions that are distributed across the tops of their upper and lower backs.
Sometime the lesions will spread down the sides of the body too. You may notice:
- Small red bumps called papules
- Large, ulcerated plaque-like lesions that are draining small amounts of fluid
- Bleeding areas of skin
- Signs your dog is in pain when you touch the affected areas
- Lethargy and/or fever in the first few days
If you notice these symptoms, please contact your veterinarian promptly. Dogs with post-grooming furunculosis or other deep skin infections affecting a large portion of their skin may be extremely painful. It is important to get them relief as soon as possible.
Diagnosis of post-grooming furunculosis
The history of being recently groomed plus the appearance of your dog’s skin will often help your vet reach a post-grooming furunculosis diagnosis. However, your vet may also recommend additional skin testing like cytology or culture. These tests can help rule out other underlying causes and guide antibiotic selection.
Especially if your dog has a fever or is lethargic, your vet may also decide to run blood tests such as a complete blood count (CBC). Dogs with post-grooming furunculosis may have normal bloodwork or may have elevated white blood cells in response to the infection.
Treatment of post-grooming furunculosis
Since this is a bacterial infection, antibiotics are the mainstay of treatment. Typically, the veterinarian will start your dog on an antibiotic that he or she thinks is likely to be effective against Pseudomonas or other bacteria that tend to cause post-grooming furunculosis. Fluoroquinolone antibiotics like marbofloxacin are often a good first choice while waiting for culture results.
Once the laboratory finishes the skin culture and sensitivity, the vet can use that information to modify the antibiotic selection if indicated. Most dogs need antibiotics for at least four to six weeks. Like with interdigital furunculosis, it is important that treatment extends two weeks past the resolution of clinical signs.
Unlike most other skin conditions, clipping the fur and topical therapies aren’t a good idea for post-grooming furunculosis. Clipping the fur can cause further trauma to the affected hair follicles. And since it is best to keep the skin clean and dry, adding more moisture in the form of topical therapy could make the infection worse. Plus, most dogs are too painful to tolerate anything being applied to their skin.
Since this condition is so painful, your vet may also recommend an anti-inflammatory medication for pain control. These medications can do a nice job with helping your dog be more comfortable.
Thankfully, with therapy, the prognosis for dogs with post-grooming furunculosis is good. Like other furunculosis conditions, it is crucial to attend recheck visits every two to four weeks to ensure that treatment is working. Also, keep in mind that it may take three to four weeks before you start seeing significant improvements in your pup’s condition.
Out of the three types of furunculosis we discussed, this is the one that is most preventable. In order to avoid post-grooming furunculosis you should:
- Keep grooming products clean and dry
- Discard old bottles for soap and shampoo rather than refilling or reusing them
- Properly disinfect clipper blades and scissors
- Use gentle movements with bathing dogs, especially those with short hair coats
- Avoid brushing hairs in the opposite direction or aggressively brushing the coat with a sharp brush
- Bring any skin lesions to your vet’s attention as soon as possible
- Contact the grooming salon if your dog develops post-grooming furunculosis so they are aware of the issue and can take the appropriate steps to prevent it from happening to other dogs
Final thoughts on furunculosis
As a dog parent, we want the best for our dear companions, and it is difficult to see them uncomfortable or in pain from furunculosis. The bad news is that furunculosis can be a bit tricky to treat, primarily because it can linger for weeks on end and requires long courses of medication.
However, by promptly taking your dog to the vet as soon as you notice skin issues and following your vet’s directions to the letter, you can get your dog on the path to recovery. There is light at the end of the tunnel. Although furunculosis looks bad, it typically does respond well to treatment. And soon enough your dog can be back to his or her old happy self!
What questions do you have about furunculosis in dogs?
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