Dermatologic Causes of Lameness
One of the best parts about practicing sports or rehab medicine is not having to deal with skin disease… mostly. Feet are the exception, where suddenly skin disease is now a source of lameness - where the Venn diagrams for sports medicine and dermatology intersect.
Here is a brief summary of the most common skin conditions affecting the feet of dogs. Choosing the proper treatment for these conditions may go beyond the purview of most of the readers here, but we should all be aware of these conditions and their potential causes, enough to help the client understand what they are dealing with.
Pododermatitis is an umbrella term to describe dermatologic inflammatory disorders of the feet. Acute manifestations frequently involve edema, comedones, hemorrhagic bullae, nodules, draining tracts, ulcerations, crusting, and pain. Chronic cases might display hair loss, hyperpigmentation, thickening and/or scarring of the skin.
Pododermatitis isn’t a diagnosis unto itself, but rather a descriptive term for lesions resulting from a number of potential causes, including bacterial or parasitic infection, immune or metabolic disorders, neoplasia, and genetic disease. Underlying allergic disease is one of the most common causes, and may be indicated by skin lesions or itchiness elsewhere on the body, particularly around lip margins or ear canals.
Feet appear predisposed to inflammatory disease because of the repetitive trauma they routinely receive facilitates pathogen invasion of the skin. Because they bear more weight, the front feet are often more affected than the back feet. Similarly, an increased body condition score is also correlated with pododermatitis. Rough terrain also appears to be a factor contributing to this disease.
Foot conformation is another significant factor contributing to the manifestation of pododermatitis. Dogs with a certain conformation of the webbing between the toes, such as Pekingese and Westies, appear predisposed to foot trauma and the accumulation of debris. Similarly, dogs with more splayed feet, such as labs and border collies, are more prone to rolling of the sides of the pads and traumatizing the adjacent skin.
A subcategory of pododermatitis is a condition called interdigital furunculosis, more commonly known as interdigital cysts. They manifest as large, often hemorrhagic or draining nodules or pustules between the digits of the dorsal aspect of the foot. They affect the forefeet more frequently, especially between digits 3 and 5.
They can be secondary to a foreign body such as a foxtail or other barbed plant matter migrating from the underside of the foot, but generally such lesions only appear on a single foot. If multiple feet are affected, then other causes, the same causes that can lead to other forms of pododermatitis, are much more likely.
Foot conformation and haircoat also play substantial a roll in interdigital cyst formation; short haired dogs are predisposed. Trauma to follicles on the underside of the foot cause an inflammatory response that is driven upward, manifesting dorsally between the digits. In addition to the causes already discussed, degenerative orthopaedic foot disease leading to secondary flattening of the feet and rolling of the toes, is also a predisposing cause.
In the same way that pododermatitis is a descriptor of symptoms, and not a diagnostic term, so is vasculitis. The term, “vasculitis” refers to a number of conditions that result in inflammation of the blood vessel walls. When vasculitis affects capillaries, local blood flow is reduced. Some causes of vasculitis, such as fungal disease or lupus, can affect multiple organs. Others only affect the skin, and a subset of those only affect the feet.
Similar to pododermatitis, there are many underlying reasons why a patient may have vasculitis, including infections, immune reactions, neoplasia, immune mediated disease, or idiopathic causes. Extremities such as the ear tips, nail beds, tail tips, and foot pads are frequently affected
Foot symptoms include abnormal nail growth, bruising, hair loss, swelling, and pigment loss. Some patients present with repeated blistering of the foot pads, despite being restricted to minimal exercise. For mild cases of vasculitis affecting the skin only, treatment with pentoxifylline is frequently effective.
Corns (digital keratomas)
Corns, the scourge of greyhounds, have no confirmed cause. Some may be the result of trauma or foreign body reaction, and others may be the result of viral papilloma infection. Corns present as painful, clearly demarcated regions of conically shaped hyperkeratosis on the underside of footpads. Weight bearing pads, particularly digits 3 and 4, are the most commonly affected. There are other lesions that might look like corns but are none painful; true corns are always a source of pain or lameness.
Although greyhounds are far and beyond the breed most likely to experience corns, other purebred sighthounds and crossbreeds can develop them as well. The have also been reported in Labrador retrievers. Males are more likely to get them compared to females.
Surgically removing corns sometimes helps, but often they recur. As a result, there are a number of different treatment options, but no clear superior treatment. An excellent resource on treatment options can be found here: https://www.greyhoundhealthinitiative.org/corns/
About the Author:
Dr. David Lane owns and operates Points East West Veterinary Services based out of Squamish, BC (Canada). https://www.pointseastwest.com/ He is a specialist in canine sports medicine and rehabilitation therapy. His research on the clinical effectiveness of combining chiropractic techniques with acupuncture therapy in dogs is the first of its kind. He was the first researcher to demonstrate the link between lower back pain and canine urinary incontinence; that treating back pain can reduce or eliminate symptoms in the majority of dogs. He also developed and published a minimally invasive surgical technique for resolving biceps tendon injury in dogs.
Current areas of interest include documenting success rates when using stem cells to repair partially torn tendons, and developing a treatment algorithm for addressing injury to the biceps tendon.
His work with sporting dogs has brought him to numerous regional and national events, as well as travelling with the national team to the World Agility Championships in Spain and the Netherlands.