Canine pododermatitis is a common clinical presentation that usually presents as either paw licking or lameness with variable additional, nonspecific clinical signs. There are many causes for pododermatitis and widely differing diseases can present in similar ways, so a careful systematic approach and definitive diagnosis are essential. This lecture will review the more common causes of pododermatitis in the dog and, by means of case presentations, outline the clinical approach. It is beyond the scope of this lecture to discuss treatment of such a wide range of conditions. Table 1 lists the more common causes of pododermatitis.
Approach to Pododermatitis
A methodical, systematic approach is required. This should include detailed history taking including age of onset, seasonality, presence or absence of signs suggestive of systemic involvement, and whether other areas of the integument are involved. Aspects of management should be explored.
A full physical examination should be performed along with careful examination of not just the paws but also the entire integument.
Hair plucks, skin scrapes, trichograms and cytology are indicated in most cases along with culture and sensitivity testing in cases of deep pyoderma. Biopsy procedure may be required to obtain samples for tissue culture and histopathological examination. Depending on the presentation, further tests include complete blood counts, serum biochemistry and endocrine analysis, diet trials, intradermal testing and/or allergen IgE serology.
Pododemodicosis may be juvenile or adult onset and can be a sequela to treatment of generalised demodicosis. Typically, cases present with a history of foot licking and, in more severe cases, lameness. The paws alone may be affected or there may be more widely distributed disease. Signs include erythema, scaling, crusting, hyperpigmentation, comedones, patchy alopecia, and variable swelling with or without secondary deep pyoderma. Regional lymphadenopathy may be marked. This condition may be misdiagnosed as atopic dermatitis due to the presence of pedal pruritus. Demodicosis should always be the first rule out in any case of pododermatitis involving haired skin.
Canine atopic dermatitis (CAD) frequently presents with pedal pruritus. This is a complex pruritic and inflammatory skin disorder of young dogs with well-recognised breed predilections. The onset is usually from 6 months to 3 years of age. Initial clinical signs are of nonlesional pruritus, typically affecting one or more areas including the face, ears, paws, limbs, ventrum and perineum and saliva staining in white-haired dogs. As disease progresses, self-trauma can lead to significant alopecia that can be confused with demodicosis. More chronic lesions may present with swelling, excoriation and secondary pyoderma and Malassezia dermatitis. The diagnosis is made on the combination of history, clinical signs and ruling out other pruritic skin diseases but diet trials and intradermal/serological testing would be indicated to identify putative causative allergens for avoidance and/or allergen immunotherapy.
Malassezia dermatitis is a common cause of pododermatitis and pedal pruritus. It results from overgrowth of the yeast Malassezia pachydermatis, although occasionally other Malassezia spp. may be involved. Clinical signs include pedal pruritus, erythema, greasy exudation, scaling and alopecia over the dorsal interdigital webs and between the footpads along with brown staining over the proximal nails. Diagnosis is made on cytology.
Malassezia dermatitis usually arises secondary to an underlying condition such as atopic dermatitis, and identification and management of the infection may be key to controlling pruritus.
Pyoderma is also a common cause of pododermatitis. Most cases involve Staphylococcus pseudintermedius but a wide range of other gram-positive and gram-negative organisms may be isolated. Clinical signs vary depending on the depth of infection. Superficial infections tend to affect the interdigital webs resulting in erythema and pruritus. Pustules, papules and collarettes are usually not seen. Signs of deep pyoderma include paw licking, lameness, swelling, haemorrhagic bullae, draining tracts and crusting involving the interdigital webs, the plantar aspects of the paw and the footpad margins. Pyoderma is a secondary disease and is always recurrent unless the underlying cause can be identified and corrected.
Chronic Inflammatory Pododermatitis
There are cases where, despite thorough workup, a definitive underlying cause cannot be identified. Such cases have been defined as idiopathic pododermatitis3 and are often refractory to therapy. A form of lymphoplasmacytic pododermatitis that responded to immunomodulatory therapy has been reported, although the authors conceded that this was probably a reaction pattern rather than a defined clinical entity.4 Another study described a group of cases with the formation of comedones and cysts over the plantar interdigital skin which periodically rupture and lead to repeated episodes of pyogranulomatous dermatitis and draining tracts. A laser surgical technique was described for treatment.5
In the author's experience, apparently idiopathic cases are often multifactorial and may involve poor foot conformation, deep pyoderma, allergies, and underlying immunosuppressive disorders. Signs include marked soft tissue swelling resulting in weight bearing on haired skin, interdigital abscessation and draining tracts.
A thorough workup is required and every attempt should be made to identify factors contributing to disease. Once infections have been treated, some cases benefit greatly from anti-inflammatory or immunomodulatory therapy with glucocorticoids or ciclosporin. Partial or complete fusion podoplasty may be required if cases are refractory to medical therapy.
Diseases Resulting in Footpad Involvement
Pemphigus foliaceus is an uncommon, sterile, autoimmune, pustular skin disease resulting from the production of autoantibodies targeting desmosomal proteins. This results in the process of acantholysis and subcorneal pustule formation. The disease typically affects middle aged to older dogs. Breed predispositions include the Japanese Akita, Chow Chow, cocker spaniel, Labrador retriever and Dachshund.6 The nasal planum, face, pinnae and footpads may all be affected, although lesions may be generalised. Occasionally, disease is confined to the footpads7 with scaling, crusting, erosions and hyperkeratosis. Differential diagnoses include superficial necrolytic dermatitis, zinc responsive dermatosis, dermatophytosis and cutaneous lymphoma.
Other Autoimmune Diseases8
Other autoimmune diseases that typically present with footpad ulceration include pemphigus vulgaris, lupus erythematosus, erythema multiforme, toxic epidermal necrolysis, mucous membrane pemphigoid, epidermolysis bullosa, and vasculitis. They may be secondary to underlying systemic disease or drug eruptions and severe presentations may be potentially life threatening.
Hepatocutaneous syndrome (necrolytic migratory erythema, superficial necrolytic dermatitis, metabolic epidermal necrosis).9
Hepatocutaneous syndrome is a necrotising skin condition of dogs associated with internal disease, most commonly a hepatopathy but glucagonoma, feeding mycotoxin contaminated foodstuffs and anticonvulsant therapy have been reported. It is hypothesized that keratinocyte damage due to cellular starvation or nutritional imbalance leads to skin lesions.
This is a disease of older dogs that present with erosions, ulcerations, erythema, alopecia, crusting and scaling over the muzzle, periocular skin, elbows, hocks, ventrum, scrotum and footpads. Concurrent lethargy, inappetence, weight loss and diabetes mellitus are common. Footpad involvement results in fissuring, erosions, crusting and pain.
Congenital Footpad Hyperkeratosis and Fissuring
Congenital footpad hyperkeratosis is recognised in the Dogue De Bordeaux, and Irish and Kerry Blue terriers. There may be involvement of the nasal planum. Congenital nasal parakeratosis has been reported in the Labrador retriever which results in thick hyperkeratosis of the dorsal aspect of the nasal planum with or without footpad involvement.
These conditions are genodermatoses and tend to present in young dogs. Fissuring and secondary infection leads to pain on walking and reluctance to exercise on hard ground.
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