“It’s pretty common to see dogs with tumors on their feet,” says John Berg, DVM, a soft tissue surgeon at Tufts’s Foster Hospital for Small Animals. Likewise, the feet “are among the primary areas where dogs become affected by allergies,” according to Tufts veterinary dermatologist Andrea Lam, DVM. Then there are diseases that strike the footpads specifically: liver disease, certain autoimmune diseases, and an illness that compromises blood flow to the foot. If you’re thinking that a dog’s feet carry perhaps more than their fair share of health risk, you’re right.
Istock
Herein, a guide to some of the most common foot problems among dogs — and how to treat them.
Evidence of Allergies in Dog Paws
The reason that evidence of allergies is so often found on a dog’s feet is that there’s not much hair on and between the toes. “Hair acts as a barrier,” Dr. Lam says, so absorption of environmental allergens like pollen, dust, mites, or mold through the skin is easy if the hair coat is sparse. It’s true for any area on a dog’s body where the hair is relatively thin, she says — the ears, under the “arms,” and in the groin area as well.
There’s also an added reason that allergies manifest themselves on a dog’s feet more than on other parts of the body. “Those areas between the digits are such tight, enclosed spaces,” Dr. Lam says, “so a lot of moisture gets trapped. And along with the inflammation caused by allergies, there’s added heat. The increased surface temperature combined with the increased moisture is a perfect set-up for infections secondary to the allergies themselves — bacterial infections or yeast infections” that lead to noticeable lesions of their own. Making matters worse is that a dog made uncomfortable or itchy by allergies will lick or chew his feet and exacerbate the inflammation.
An owner might see, along with swelling, redness or discharge, a rusty color between the toes that results from salivary staining. People often think that’s blood, Dr. Lam says, but “it’s just a reaction when compounds in saliva are oxidized, sort of like rusting. It might be particularly noticeable if a dog is white or blonde. But foot lesions can be very subtle,” she cautions, “and sometimes if you’re not looking for it, you might miss it.” That’s why it’s good to take your dog for regular wellness exams. A close look at the feet is part of the physical.
If the veterinarian does diagnose allergies, it needs to be determined whether they are allergies to substances in the environment or allergies to particular food ingredients. Most of the time they will be allergies to things in the environment, which affect 10 percent of dogs. Compared to that, food allergies are exceedingly rare.
If a definitive diagnosis shows that the problem is indeed allergies to environmental substances, the dog will be put on one or more of the following: steroids to reduce inflammation during flare-ups; cyclosporine to suppress the overreactive immune system that is causing the symptoms; and allergen-specific immunotherapy, namely allergy shots. Frequent baths with a soft, moisturizing shampoo may also be recommended.
Suspected food allergies that cause reactions in the skin of a dog’s foot can be diagnosed and treated by a vet board-certified in nutrition, although a veterinary dermatologist and sometimes your dog’s own vet can work with food allergies, too. Finding the culprit is a process of trial and error.
Of course, if a secondary bacterial or fungal infection has developed because of an environmental or food allergy, antibiotics or anti-fungal medications must be given.
Diseases Affecting the Footpads of Dogs
Allergies generally affect the skin on a dog’s foot and toes, and also between the toes, but some conditions break out on a dog’s footpads — those black shock absorbers under their toes and on their “palms.” Because dogs don’t wear shoes, a problem with their footpads can really affect their gait, in addition to making them very uncomfortable. “We might see thickening of the pads — or erosion,” says Dr. Lam. Footpad diseases can also sometimes signal that something is wrong with an internal organ. “Diseases affecting the footpads are generally more concerning than allergies,” Dr. Lam says, “because they can be a serious sign of internal disease.” Three conditions in particular are on the radar of veterinary dermatologists like Dr. Lam.
Pemphigus Foliaceus: This is an autoimmune disease — one of the most common that dogs get — in which the immune system attacks the little proteins that hold together a dog’s skin cells. As a result, says Dr. Lam, “the skin cells flow apart prematurely and little pustules form on the surface of the foot pads.” But you never see the pustules, she says, only crust developing on the footpads, because the dog is constantly walking. The pressure of the footsteps breaks open the pustules as they form. The condition has to be treated not just because it can prove painful but also because it leaves a dog prone to secondary infections. Once the skin is vulnerable, it’s all too easy for pathogens to make their way inside the body.
Pemphigus foliaceus is diagnosed with a biopsy. “If there’s a lesion on a toe pad, we just use sedation,” Dr. Lam says. “But if there are lesions on the main pad we do anesthesia. We try not to take the biopsy from where a dog bears weight because that’s more painful, with a longer recovery time.”
Once the disease is diagnosed, it’s treated with immune-suppressant drugs. And once the problem has abated, the dog remains on the drugs for life but at a lower, maintenance dosage than during the initial treatment phase. At lower doses, the drugs work more like anti-inflammatories than immune suppressants.
Hepatocutaneous Syndrome: This is one of those footpad diseases that signals something is wrong internally. Manifested by a thickening of the pads, it usually means there’s a problem with the liver, specifically, that the liver is not utilizing proteins the way it’s supposed to. The liver helps break down proteins into amino acids, after which they are reassembled to create new proteins as needed. Some of those proteins are necessary to help build skin. But with hepatocutaneous syndrome, several amino acids are greatly reduced in circulation. Lesions on the footpad are one of the first signs to develop, often long before your dog would start to feel sick from a compromise in the workings of his liver.
Diagnosis includes a blood workup to check liver enzymes. An abdominal ultrasound can be very helpful as well. “The liver looks a very specific way when this disease is occurring,” Dr. Lam says. In rare cases, the disease is found not to indicate a problem with the liver but with the pancreas, which secretes hormones that guide in protein breakdown and synthesis. “We don’t know what causes it in either organ,” comments Dr. Lam. “It’s idiopathic,” meaning arising from unknown origin.
Unfortunately, she adds, “the prognosis is very poor.” The treatment is to give amino acids intravenously and perhaps supplemental protein powders to provide the system with the right proportions of amino acids, but “on average, dogs live six months after diagnosis. I did once manage a case for two years after diagnosis,” Dr. Lam reports, but such a life expectancy with hepatocutaneous syndrome is not to be expected. One thing that helps dogs remain more comfortable after diagnosis is treatment of any secondary bacterial or fungal infections that arise because of breaks in the compromised skin of the footpads.
Ischemic Dermatopathy: In dogs with this condition, blood flow to the skin has been compromised. The disease “presents as erosions or ulcers in the central portion of the footpad,” whether the pad for any of the digits or the central pad, Dr. Lam says. They look “very, very circular, almost like somebody took a hole punch to the pads. It’s very striking.”
Usually, ischemic dermatopathy comes on for reasons unknown, but in some cases it has been linked to the rabies vaccine. Dr. Lam is quick to point out that the disease is very uncommon, whatever the cause. “I see the rabies-induced kind once or twice a year,” she says, “and never even heard of it in Canada,” her country of origin, where she went to veterinary school. Even in California, where she did a residency and where the condition was diagnosed more commonly, she came across a case only once every two to three months.
Because the disease is so visually distinct, a biopsy for diagnosis is generally not necessary. “We can start treatment based on how things look,” says Dr. Lam. The therapy consists of steroids to help reduce pain and inflammation at the beginning. But long-term, she comments, “we usually use pentoxifylline.” It has anti-inflammatory properties of its own, but even more important, it makes the dog’s red blood cells very flexible, bendable. That allows them to “change their shape and creep into all the little blood vessels that may have been damaged,” Dr. Lam says, filling in the little circular erosions in the process.
In some cases, says Dr. Lam, “we tell the owner that the dog is not a good candidate for rabies vaccines. And in some states that’s permitted by law. If it’s not, we have to support the dog with medication for ischemic dermatopathy prophylactically. They’re on a maintenance dosage pretty much for life, and the month before the vaccine, we’ll up it.”
Tumors in Dogs’ Feet
“A tumor on a dog’s foot may be benign or malignant, but either way, it usually needs to be removed for the dog to maintain his ability to get around,” says Dr. Berg, the editor-in-chief of Your Dog as well as a soft tissue surgeon. As far as malignant, or cancerous, tumors, one type that fairly commonly affects a dog’s feet is called squamous cell carcinoma. A carcinoma is a cancer that arises from epithelial tissue, including tissues that make up various body linings like the skin or mucous membranes. Squamous cell carcinomas may also originate in the bone of a dog’s toe that houses the nail bed. Each toe has three bones, just like a person’s fingers or toes. The nail beds are located in the bone closest to the nail, which is called p3.
A breed that has a tendency to be affected by squamous cell cancer of the nail bed is the standard poodle. Black ones in particular are prone. But the owner of any dog whose nail falls out without any trauma to the spot should be suspicious and take his pet to the vet to see if the cause might be squamous cell carcinoma of the nail bed. The good news is that squamous cell carcinomas don’t tend to metastasize, so they have a good prognosis after surgery to amputate the affected toe.
Sometimes the cancer affects multiple digits in different feet, not by metastasizing but simply by arising in several spots. “I had a dog once that over time developed at least four of these,” Dr. Berg says. “Because a dog wouldn’t be able to walk if you removed every digit, we ended up prophylactically removing the p3 bone of every one of his digits. His gait remained intact, and he didn’t develop any more tumors.”
Other common canine cancers that affect dogs’ feet include mast cell tumors (originating in the skin or subcutaneous fat just under the skin); soft tissue sarcomas (sarcomas arise from connective tissue like nerves, muscles, and tendons); and osteosarcaroma (bone cancer).
The difficulty is that except for the smallest tumors, they’re difficult to excise. “There’s not much extra skin on the foot,” Dr. Berg explains. “It’s tight, so it’s not easy to do a wide incision, cut away the tumor, then close the incision.”
That’s why veterinary surgeons generally end up doing amputations of toes, where many of the tumors occur. It may sound drastic, but dogs function extremely well without a toe and are absolutely normal except for the slight cosmetic change.
Of course, when ampution of a toe is suggested to most owners, they become concerned about their dog’s being able to bear his own body weight as he moves about. “We always say that in dogs, the weight-bearing toes are digits three and four,” Dr. Berg points out. Those digits, corresponding to our middle finger and our ring finger, are the main ones involved in walking and running. Their counterpart to our thumb — the dewclaw — doesn’t even touch the ground. “It’s vestigial” in dogs, Dr. Berg says, meaning it’s an anthropologic leftover from an earlier time, serving no purpose today. The dog’s counterpart to our index finger and pinky are thought not to be as critical for ambulation as digits three and four.
But even amputation of one of the weight-bearing digits will not result in a dog’s loss of ability to get around. Once the incision heals, the gait will be perfectly normal. Indeed, Dr. Berg says, dogs that lose two toes will return to normal function, although it takes a little longer — up to a few weeks. He points out that “it’s better to do that, however, than to let a tumor get out of control where the only option is to remove an entire leg.” Sometimes two toes have to be removed when a tumor grows where they come together, at the webbing near their base, so to speak.
Common Trauma to the Foot
Sometimes a foot problem is not about cancer or an allergy or even a footpad disease but results from a car accident or other injury, such as a bad burn.
If it’s the big central pad of the foot — the equivalent of our palm — removal may not be an option because it becomes much more difficult to bear weight on the foot without it. “One thing we’ll sometimes do,” Dr. Berg says, “is take the pad tissue from some of the toes to rebuild the tissue of the central foot pad. The big pad doesn’t have to be removed often, but if you have to excise more than about 30 percent of it, you need to be able to replace what’s missing for the dog to be able to ambulate properly.”
Sometimes the solution to foot trauma is much simpler. If there’s a laceration, for instance, it can be sutured. Certain fractures can be tended to as well. A fractured toe usually gets amputated because it’s too complicated — and expensive — to reset the bone for healing. But a dog who suffers a fracture of certain other bones in the foot might get different treatment — a procedure to put the bone back into proper position and give the dog his full range of motion.
