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Veterinary Focus

Issue number 28.1 Other Scientific

How to treat canine pododermatitis

Published 06/08/2020

Written by Rosanna Marsella

Also available in Français , Deutsch , Italiano , Polski , Português , Русский and Español

Dogs with sore feet may at first sight be mundane and easy to treat, but pitfalls await the unwary; Rosanna Marsella takes a personal look at what can be a remarkably complex clinical disorder and gives some useful tips for diagnosis and treatment

How I approach… Canine pododermatitis

Key Points

Canine pododermatitis can be primary or secondary in nature, and the clinician should follow a logical approach to ascertain the underlying etiology.


Identifying the distribution and type of primary lesions are essential in making a diagnosis.


Demodex mites should always be considered as a possible cause of pododermatitis.


Some causes of pododermatitis affect not only the haired skin but also the nails, which can help in the differential diagnosis of the underlying disease.


Canine pododermatitis is a very common presentation in veterinary dermatology, but since it can result from many different causes it is important to have a logical and sequential diagnostic approach in order to successfully identify the primary disease responsible. With the correct diagnosis, clinical management becomes easier and more targeted. However, as with many dermatological cases, secondary infections and chronic skin changes frequently complicate the clinical picture, whatever the underlying disease, so it is always important to consider the primary, secondary and perpetuating factors for pododermatitis (Table 1). 

Primary factors

Pruritic

  • Atopic dermatitis
  • Food allergy
  • Contact allergy
  • Flea allergy
  • Demodicosis
  • Hookworm dermatitis1

Non-pruritic

  • Hypothyroidism
  • Demodicosis
  • Dermatophytosis1,2
  • Leishmaniasis2
  • Immune-mediated (e.g., vasculitis2, symmetric lupoid onychodystrophy2)
  • Autoimmune (e.g., pemphigus foliaceus)
  • Metabolic (e.g., necrolytic migratory erythema1)
  • Neoplastic (e.g., mycosis fungoides1)
Secondary factors
  • Bacterial infection
  • Malassezia infection
Perpetuating factors
  • Fibrosis/scarring
  • Interdigital cysts

Table 1.  Causes of pododermatitis.

1 Diseases that can also manifest with hyperkeratosis of the footpads
2 Diseases that can affect the nails

Whilst primary causes of pododermatitis may be pruritic or non-pruritic, secondary infection is frequent and will often cause pruritus, so it is not uncommon for many dogs with pododermatitis to present with pruritus as one of the main complaints. It is therefore important to treat any infection and then re-evaluate for pruritus to effectively identify the triggering disease.

How are the lesions distributed?

Primary causes of pododermatitis are diseases that can directly target the feet, although many of them may also affect other body regions. It is therefore important to identify the distribution of lesions on clinical examination. This allows the clinician to appropriately rank the various differential diagnoses in order of likelihood.

Some diseases affect all four feet, while others only the front feet, at least initially. An example of the former is contact allergy, an example of the latter is atopic dermatitis, which typically starts on the forepaws and then progresses to all four feet. Flea allergy, on the other hand, tends to primarily affect the back feet.

What do the primary lesions look like? 

Figure 1. Pruritic papules on the palmar-plantar aspect of all four feet is a typical clinical presentation if a carpet or a grass causes a contact allergy. © Rosanna Marsella
Figure 1. Pruritic papules on the palmar-plantar aspect of all four feet is a typical clinical presentation if a carpet or a grass causes a contact allergy. © Rosanna Marsella

It is important to know what type of primary lesions are associated with each disease (e.g., papules, pustules, bullae). For example, contact dermatitis is associated with a primary papular eruption, so if the contact allergy is to either a carpet or a grass. pruritic papules on the palmar-plantar aspect of all four feet would be the expected clinical presentation 1. Other contact areas that are also frequently affected are the muzzle, perineal area and ventral abdomen (Figure 1) (Figure 2a) (Figure 2b).

Figure 2a. Another contact area that is also frequently affected is the muzzle. © Rosanna Marsella
Figure 2a. Another contact area that is also frequently affected is the muzzle. © Rosanna Marsella
Figure 2b. Another contact area that is also frequently affected is the ventral abdomen. © Rosanna Marsella
Figure 2b. Another contact area that is also frequently affected is the ventral abdomen. © Rosanna Marsella

An example in which the primary lesion is a pustule is pemphigus foliaceus. As pustules are fragile, many patients have crusts as remnants of dried-up pustules (Figure 3). Pemphigus foliaceus in dogs typically affects the face (as a “butterfly“ pattern affecting the periocular region, the bridge of the nose and nose itself) and the inner surface of the pinnae 2. Layers of dry pustules may be noticeable on the footpads (Figure 4), especially on the edges of the pads. 

Figure 3. A dog with pemphigus foliaceus. As the pustules are fragile, crusts (remnants of dried up pustules) may be seen. © Rosanna Marsella
Figure 3. A dog with pemphigus foliaceus. As the pustules are fragile, crusts (remnants of dried up pustules) may be seen. © Rosanna Marsella
Figure 4. Layers of dry pustules may be noticeable on the footpads if a dog has pemphigus foliaceus. © Rosanna Marsella
Figure 4. Layers of dry pustules may be noticeable on the footpads if a dog has pemphigus foliaceus. © Rosanna Marsella

Another extremely important primary cause of pododermatitis is Demodex mites. In fact, demodicosis should always be included on the list of differential diagnosis for canine pododermatitis 3, as this disease can manifest in a variety of ways. It can present with erythema and pruritus, and may look very similar to an allergic foot; many affected dogs also have a pruritic face and can easily be mistaken as being allergic (Figure 5). Because of this, any pruritic foot should be scraped for Demodex spp. before assuming that it is allergy and therapy such as glucocorticoids or oclacitinib is initiated. Comedones are another manifestation of demodicosis (Figure 6); they have a characteristic gray discoloration and are due to plugging of the hair follicles by large number of mites. Their presence should always alert clinicians to perform a skin scape, although if the foot is too swollen and painful (Figure 7), hair plucks may be considered, with the understanding that the sensitivity of hair plucks is inferior to a deep skin scrape. As the result of folliculitis, most (but not all) affected dogs present with hair loss. Interestingly, long-haired breeds such as Yorkshire and Maltese Terriers do not appear to develop alopecia as often as short-haired breeds. 

Figure 5. A dog with Demodex mange. Many affected dogs have a pruritic face and can easily be mistaken as being allergic. © Rosanna Marsella
Figure 5. A dog with Demodex mange. Many affected dogs have a pruritic face and can easily be mistaken as being allergic. © Rosanna Marsella
Figue 6. Many dogs with demodicosis develop comedones, with a characteristic gray discoloration. © Rosanna Marsella
Figue 6. Many dogs with demodicosis develop comedones, with a characteristic gray discoloration. © Rosanna Marsella
Figure 7. Some dogs with demodicosis develop extremely painful interdigital lesions. © Rosanna Marsella
Figure 7. Some dogs with demodicosis develop extremely painful interdigital lesions. © Rosanna Marsella

What else helps with diagnosis?

When considering other causes of pododermatitis, it is important to remember that some diseases involve both haired skin and footpads, while others do not. For example, atopic dermatitis affects only the haired skin, but autoimmune diseases like pemphigus foliaceus may also affect the footpads and present with crusting and hyperkeratosis. There are many differential diagnoses for pododermatitis and hyperkeratosis. One of the most important is superficial necrolytic dermatitis (SND), which targets both the footpads and other areas of the body such as the genitalia and the commissures of the mouth (Figure 8) (Figure 9) 4. This is a disease of geriatric animals and is linked to metabolic dysfunction and amino acid deficiency. The footpads in this disease show cracking and fissures, rather than the dry layers of pustules seen with pemphigus. The appearance of the lesions, the different distribution of lesions and the age of the patient are all clues which help the clinician to rank the diseases and prioritize between the likelihood of pemphigus foliaceus and SND.

Rosanna Marsella

The distribution and appearance of the lesions, along with the presence or absence of pruritus, are real pointers as to the possible underlying etiology.

Rosanna Marsella

Figure 8. A dog with superficial necrolytic dermatitis. The footpads in this disease show cracking and fissures rather than dry layers of pustules as in the case of pemphigus. © Rosanna Marsella
Figure 8. A dog with superficial necrolytic dermatitis. The footpads in this disease show cracking and fissures rather than dry layers of pustules as in the case of pemphigus. © Rosanna Marsella
Figure 9. Superficial necrolytic dermatitis can also target the commissures of the mouth (a) and the genitalia (b). © Rosanna Marsella
Figure 9. Superficial necrolytic dermatitis can also target the commissures of the mouth (a) and the genitalia (b). © Rosanna Marsella

For both diseases skin biopsy is diagnostic, and it is important to stress the importance of a definitive diagnosis by biopsy rather than simply relying on clinical impression, as the treatments are completely different. In pemphigus foliaceus acantholytic cells and superficial pustules are hallmarks of the disease, while parakeratosis, spongiosis and epidermal hyperplasia of the basal cell layer (“red-white-blue” layers) are considered characteristic for SND. In pemphigus, treatment with glucocorticoids and other immunosuppressive agent are the standard of care, whereas in SND glucocorticoids are usually contraindicated, as many affected dogs are either diabetic or borderline diabetic. In these cases it is crucial to investigate the underlying metabolic disease and to institute appropriate nutritional therapy with amino acids, zinc and essential fatty acids.

Figure 10. Some cases of Trychophyton infection can develop dramatic lesions which may look very similar to pemphigus foliaceus clinically. © Rosanna Marsella
Figure 10. Some cases of Trychophyton infection can develop dramatic lesions which may look very similar to pemphigus foliaceus clinically. © Rosanna Marsella

It is important to stress that acantholytic cells, traditionally considered a hallmark of pemphigus, can also be caused by other diseases such as contact allergy and dermatophytosis. In any disease where a severe neutrophilic inflammatory infiltrate develops, acantholysis may ensue as a consequence of the proteolytic effect of degenerating neutrophils. Since some cases of Trychophyton may resemble pemphigus foliaceus clinically (Figure 10) it is important to consider this as a differential diagnosis; misdiagnosis of dermatophytosis as pemphigus could be problematic, as glucocorticoids are inappropriate for ringworm cases. In these patients systemic antifungal therapy is necessary for many months, and itraconazole (5 mg/kg PO q24H) is commonly used as it concentrates in keratin and has residual activity after discontinuation of therapy. Terbinafine (20 mg/kg PO q12H) is also an excellent choice, due to its keratinophilic properties and its ability to persist in the keratin for extended periods of time.

What else can affect the feet? 

Figure 11. Vasculitis typically presents on the feet with ulcers in the center of the pads. © Rosanna Marsella
Figure 11. Vasculitis typically presents on the feet with ulcers in the center of the pads. © Rosanna Marsella

Other diseases that can affect the feet are syndromes such as vasculitis and erythema multiforme. Vasculitis is a type III hypersensitivity that can be due to many causes and is triggered by a variety of antigenic stimuli 5. The immune complex deposition may occur on the feet and ears, as well as other areas of the body. It may be initiated by drugs, vaccines, or infectious causes such as tick-borne diseases. The typical presentation on the feet is the presence of ulcers in the center of the footpads (Figure 11), the ulcer size varying depending on the severity and the size of the blood vessels affected. Diagnosis is based on clinical presentation and biopsy of an early lesion. It is important for the clinician to identify and treat (where possible) the underlying cause. Many of these cases require glucocorticoids at immunosuppressive doses in combination with pentoxifylline, and some patients necessitate prolonged treatment to completely extinguish the immunologic response. 

Figure 12. The classic lesions of erythema multiforme are erythematous macules with a paler central area; they can affect many areas of the body, including the feet. © Rosanna Marsella
Figure 12. The classic lesions of erythema multiforme are erythematous macules with a paler central area; they can affect many areas of the body, including the feet. © Rosanna Marsella

Erythema multiforme should also be included in the category of immune-mediated diseases that can cause pododermatitis. This is a clinical syndrome rather than a specific diagnosis, and again the clinician needs to identify the triggering disease in order to be successful with therapy. The classic lesions are erythematous macules with a paler central area (Figure 12); they may be found on many areas of the body, including the feet. It is important to take a thorough history of medications and vaccines, keeping in mind that drugs can trigger this type of cutaneous reaction, even if well tolerated previously. Definitive diagnosis is by biopsy, in which individual apoptotic cells are evident. Immunosuppressive treatments are typically prescribed while addressing the triggering cause.

Don’t ignore the nails!

Some causes of pododermatitis not only affect the haired skin but also the nails 6. Various changes to the normal nail structure may be noted (Table 2). Two classic examples are symmetric lupoid onychodystrophy and dermatophytosis (Figure 13). In parts of the world where Leishmania is present, this disease should be considered if onycogriphosis (hypertrophy and abnormal claw curvature) is noted. Table 3 offers a more complete list of diseases that can present with pododermatitis and affected nails. 

Figure 13. Microsporum gypseum infection in two dogs; some cases of dermatophytosis can involve the nails, with secondary pododermatitis. © Rosanna Marsella
Figure 13. Microsporum gypseum infection in two dogs; some cases of dermatophytosis can involve the nails, with secondary pododermatitis. © Rosanna Marsella

Onychoclasis
Breaking of the claw
Onychocryptosis
Ingrown claw
Onychodystrophy
Abnormal claw formation
Onychogryphosis
Hypertrophy and abnormal claw curvature
Onychomadesis
Sloughing of the claw
Onychomalacia
Softening of the claw
Onychorrhexis
Longitudinal striations associated with brittleness and breakage of the claw
Onychoschizia
Splitting and/or lamination of the claw, usually beginning distally
Paronychia
Inflammation of the nail fold
Table 2. Terminology for common abnormalities of the nail.

 

Symmetrical lesions
  • Dermatophytosis
  • Symmetric lupoid onychodystrophy
  • Inflammation extending to the nail bed
    • Bacterial
    • Demodicosis
    • autoimmune (e.g., pemphigus)
    • drug eruptions
    • metabolic diseases (e.g., necrolytic migratory erythema)
  • Keratinization defects (e.g., primary seborrhea of the Cocker Spaniel)
  • Congenital and hereditary defects
    • dermatomyositis of Shetland Sheepdogs and Collies
    • acrodermatitis of Bull Terriers
  • Nutritional deficiency (e.g., zinc)
  • Vasculitis
  • Idiopathic onychomadesis (German Shepherd dogs, Whippets, English Springer Spaniels)
  • Idiopathic symmetric onychodystrophy (Siberian Husky, Rhodesian Ridgeback, Dachshund)
  • Leishmaniasis
  • Malassezia
Asymmetrical lesions
  • Bacterial – most common; always a secondary issue
  • Trauma
  • Neoplasia (e.g., squamous cell carcinoma, melanoma, mast cell tumor, keratoacanthoma, inverted papilloma)
Table 3. Differential diagnoses for diseases of the claws.

Figure 14. Symmetric lupoid onychodystrophy in young dogs. The abnormal nails are painful and friable, and slough easily. © Rosanna Marsella
Figure 14. Symmetric lupoid onychodystrophy in young dogs. The abnormal nails are painful and friable, and slough easily. © Rosanna Marsella

Symmetric lupoid onychodystrophy has been reported in Labradors, German Shepherds, Rottweilers and Boxers 7 and has some features of lupus, although affected dogs do not have systemic disease. Cases are usually young animals, with sudden-onset nail loss (Figure 14) which is associated with variable degrees of pain and pruritus. Paronychia may be seen. Secondary bacterial infections are common and contribute to the pain and pruritus. The natural course of the disease involves partial re-growth of friable, abnormal nails that continue to be sloughed. Blood work (i.e., complete blood cell count (CBC), chemistry panel and antinuclear antibody (ANA)) is unremarkable, and diagnosis is obtained by amputation of P3 and histopathology. Therapy includes the use of high doses of essential fatty acids or glucocorticoids. Tetracycline and niacinamide have been used as they have immunomodulatory properties, but improvement may not be seen for a couple of months. Pentoxifylline (15-20 mg/kg PO q8H, given with food to minimize GI problems) has been found to help in some cases; the improvement may be due to the multiple immune-modulatory properties of the drug. Secondary infections need to be addressed at the same time. In some cases this disease has been linked to a food reaction, and some dermatologists recommend an elimination trial to rule out the possibility of food as a precipitating factor. Removal of P3 and the claw on affected digits may be necessary in some cases.

What about chronic changes and perpetuating causes?

As noted earlier, whatever the primary cause of pododermatitis, scarring and foreign body reaction to free keratin in the dermis can develop due to infection and the destruction of hair follicles (furunculosis). The inflammatory response built against bacteria and fragments of hairs leads to swelling, pain and fibrosis over time (Figure 15). Some dogs tend to develop cystic lesions as the body attempts to wall off foreign material (Figure 16) 8. These nodules are frequently a source of recurrence as they can act as a starting point for new bouts of infection. Short-coated dogs are more prone to this type of reaction; it is believed that the short prickly hair in the interdigital spaces tend to mechanically drive the bacteria into the skin on the opposite side. These cases can be frustrating to treat and often require long courses of oral antibiotics and topical whirlpool therapy with antimicrobial agents like chlorhexidine or benzoyl peroxide. Culture and sensitivity is strongly encouraged in these cases to identify the most effective antibiotic, although clindamycin or fluoroquinolones are usually a good choice, as they achieve excellent penetration into the deep layers of the dermis. Additionally, many cases benefit from glucocorticoids and topical antibiotics such as mupirocin. Glucocorticoids can help decrease the fibrosis and excessive inflammatory response, which sometimes hinders the resolution of the pododermatitis. Soaking with agents that may facilitate the opening and draining of these nodules (e.g., magnesium sulfate) is also beneficial. In severe cases laser surgery 9 or podoplasty may be necessary. 

Figure 15. Secondary changes in pododermatitis can involve a severe inflammatory response against bacteria and fragments of hairs, leading to swelling, pain and fibrosis. © Rosanna Marsella
Figure 15. Secondary changes in pododermatitis can involve a severe inflammatory response against bacteria and fragments of hairs, leading to swelling, pain and fibrosis. © Rosanna Marsella
Figure 16. Some dogs tend to develop cystic lesions secondary to pododermatitis as the body attempts to wall off foreign material. © Rosanna Marsella
Figure 16. Some dogs tend to develop cystic lesions secondary to pododermatitis as the body attempts to wall off foreign material. © Rosanna Marsella

So what’s the diagnostic approach?

When considering the numerous causes of pododermatitis, an initial clinical approach should minimally include cytology, deep skin scraping and a fungal culture (Table 4). Cytology can be done with a tape or a swab depending on the condition of the skin. Dry skin is better evaluated with tape impressions, while areas of exudate are suitable for direct impressions or swabs. Samples are easily stained and analyzed for the presence and type of inflammatory infiltrate, the presence of bacteria and yeasts and possibly acantholytic cells. Diagnosis of fungal infections is made by Dermatophyte Test Medium (DTM) culture of the nails (shavings or clipping taken from the most proximal portions of the nail). 

 

Clinical approach to pododermatitis case – First visit
  • Treat any secondary infection based on cytology. Bacterial culture may be needed, based on clinical history and prior response to antibiotic.
  • Perform deep skin scrapings; if positive, start therapy for Demodex; note that negative hair plucks may not completely rule out demodicosis.
  • Consider biopsy if necessary.
  • Perform fungal culture (DTM of hair, skin and possibly nails, depending on clinical presentation).
  • Do blood work (CBC and chemistry panel) if indicated, especially in older dogs and in particular if SND is a consideration.
Clinical approach to pododermatitis case – Recheck visit
  • If infection is still present, repeat culture and sensitivity tests.
  • If infection is resolved, consider primary lesions and rank differential diagnoses and formulate a diagnostic plan based on distribution and presence of pruritus.
  • Remember that some conditions will necessitate biopsy (e.g., autoimmune, immune-mediated) but that allergic skin diseases are not diagnosed by biopsy.
  • Consider conducting an elimination diet trial
Table 4. The essential aspects to consider when presented with any dog with pododermatitis can be summarized as follows.

Blood sampling (CBC and biochemistry panel) may be indicated in older dogs, and in particular if SND is a consideration, whilst the decision to biopsy or not will depend on the signalment, clinical signs and history. Bear in mind that some conditions (e.g., autoimmune or immune-mediated disease) will necessitate biopsy for diagnosis, whereas other conditions (e.g., allergic skin disease) cannot be diagnosed by biopsy. Based on the distribution and presence of pruritus, the clinician should then the rank differential diagnoses and formulate a diagnostic plan.

The clinical approach to pododermatitis requires good subject knowledge and accurate identification of primary, secondary and perpetuating factors. Omitting basic tests at the initial evaluation can mean common problems are overlooked, and appropriate treatment for secondary infections is essential. Ultimately, since many diseases can look similar, it is crucial to obtain a diagnosis rather than simply attempting to treat the clinical signs.

References

  1. Marsella R. Contact allergy. In: Veterinary Allergy Noli C, Foster A, and Rosenkrantz W (eds), Chichester, Wiley Blackwell 2014;185-190.
  2. Vaughan DF, Clay Hodgin E, Hosgood GL, et al. Clinical and histopa­thological features of pemphigus foliaceus with and without eosino­philic infiltrates: a retrospective evaluation of 40 dogs. Vet Dermatol 2010;21(2):166-174.
  3. Duclos D. Canine pododermatitis. Vet Clin North Am Small Anim Pract 2013;43(1):57-87.
  4. Outerbridge CA. Cutaneous manifestations of internal diseases. Vet Clin North Am Small Anim Pract 2013;43(1):135-152.
  5. Innerå M. Cutaneous vasculitis in small animals. Vet Clin North Am Small Anim Pract 2013;43(1):113-134.
  6. Santoro D. An approach to disease of the claws and claw folds. In: BSAVA Manual of canine and feline dermatology, 3rd ed. Jackson H, Marsella R (eds); Gloucester, BSAVA 2012;121-125.

  7. Mueller RS. Diagnosis and management of canine claw diseases. Vet Clin North Am Small Anim Pract 1999;29(6):1357-1371.
  8. Duclos DD, Hargis AM, Hanley PW. Pathogenesis of canine interdigital palmar and plantar comedones and follicular cysts, and their response to laser surgery. Vet Dermatol 2008;19(3):134-141.
  9. Perego R, Proverbio D, Zuccaro A, et al. Low-level laser therapy: case-control study in dogs with sterile pyogranulomatous pododermatitis. Vet World 2016;9(8):882-887.
Rosanna Marsella

Rosanna Marsella

Dr. Marsella is a Diplomate of the American College of Veterinary Dermatology and full Professor at the University of Florida. Read more

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