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Canine surface pyoderma
THE canine pyodermas are cutaneous, pyogenic infections that are often classified according to their depth within the skin as surface, superficial or deep.
In surface pyoderma, infection is confined to the interfollicular epidermal layers of the skin, frequently leading to erosions and ulcers. Superficial pyoderma is characterized histologically by pustule formation within the epidermis or hair follicle. In deep pyoderma, the infection extends from the hair follicle to involve dermal tissue; the term “furunculosis” is used to denote an inflammatory destruction of the hair follicle. Canine pyoderma is most often associated with staphylococcal infection, principally S. pseudintermedius (formerly S. intermedius). Decisions on the type of treatment, as well as duration, are often made based on depth of pyoderma. Topical treatment options are usually sufficient for surface pyodermas, whereas deeper infections normally require systemic antibacterial therapy. The most common forms of surface pyoderma are pyotraumatic dermatitis and intertrigo.
Pyotraumatic dermatitis (synonyms: acute moist dermatitis, hot spot) is characterised clinically by the rapid development of well circumscribed, erosive and erythematous, often slightly raised areas covered in serosanguinous to purulent exudate and matted fur. The pathogenesis of pyotraumatic dermatitis is poorly understood. In the standard text of small animal dermatology, it is classified as a surface pyoderma1. The term pyoderma denotes a cutaneous, pyogenic bacterial infection. However, later in the same text, it is stated that the lesion is produced by self-inflicted trauma and is colonised by bacteria but that it does not represent a skin infection. Thus, there is no consensus on the role of bacterial infection in the pathogenesis of these common lesions. In a study of the histopathological features of pyotraumatic dermatitis, two distinctive histopathological patterns were recognised2. One was characterised by a superficial inflammatory pattern with epidermal ulceration and a perivascular to diffuse neutrophilic infiltrate in the superficial dermis. The other pattern showed similar epidermal changes but with additional deep necrotising and suppurative folliculitis and evidence of bacteria in areas of folliculitis. The authors suggested that the second pattern was caused by pyoderma as a complicating factor in pyotraumatic dermatitis lesions. This deeper form, termed “pyotraumatic folliculitis”, frequently occurs on the face or neck and is characterised clinically by the presence of satellite papules and pustules. Lesions with and without folliculitis and/or furunculosis were also reported in a more recent study by Holm et al3. Although the lesions of pyotraumatic dermatitis are clinically quite distinctive, they must be differentiated from pyotraumatic folliculitis, since the treatment and clinical course is quite different. Flea allergy is frequently seen as the underlying cause of self-trauma but other causes of pruritus include infestations with lice and other ectoparasites, atopic dermatitis, food hypersensitivity, otitis externa or pain that causes the dog to chew, lick or scratch the skin. It has been suggested that breeds with dense undercoats are in a higher risk group owing to poor skin ventilation. Warm, humid weather has also been implicated as a risk factor. Anal sacculitis is a possible trigger for lesions around the tail base.
Intertrigo, or skin fold dermatitis, develops in areas of friction between two skin surfaces. The lesions are common in breeds with prominent skin folds, such as the Chinese Shar-Pei and Basset hound. Facial fold dermatitis is common in brachycephalic breeds, such as the Pug and Pekingese and lip fold dermatitis is prevalent in spaniels. Other affected areas include the tail and vulvar fold. This especially affects obese dogs, which can develop additional skin folds, for example along the ventral midline; but also in axillary and inguinal areas. Furthermore, pre-existing folds tend to become deeper in these individuals. In addition to skin surface damage caused by friction, microbial overgrowth is increased in skin folds with poor air ventilation, and trapped moisture caused by skin secretions, tears, saliva or urine. Concurrent diseases that decrease skin immunity, such as hormonal disorders and allergies, further promote growth of yeasts and bacteria, so skin fold dermatitis is frequently malodorous.
Clipping of the hair and cleansing are essential parts of the treatment to increase skin ventilation, remove infectious debris and enable proper assessment of the affected area. In some cases, this is sufficient to stop self-trauma and enable healing, although most cases require additional antimicrobial and antipruritic treatment. A wide array of topical and/or systemic treatments can be used in varying combinations for pyotraumatic dermatitis, but despite being very common lesions, few studies have been published that critically evaluate these options. One large clinical trial in the UK compared a topical gel containing fusidic acid and betamethasone (Fuciderm, Dechra) applied twice daily, with systemic treatment using clavulanic acid potentiated amoxicillin and parenteral dexamethasone4. Fuciderm was shown to be equally effective when compared with seven days of the systemic treatments. Another study compared a topical combination treatment consisting of neomycin and prednisolone with either component used alone. The antibiotic alone was found to be more effective than the glucocorticoid alone but the combined product was found to be superior in efficacy when treating pyotraumatic dermatitis5. Failure of a pyotraumatic dermatitis lesion to respond rapidly to topical antibiotic/steroid combinations should prompt an evaluation of compliance and the original diagnosis; lack of response might indicate pyotraumatic folliculitis with deep bacterial infection. Palpation of the affected area helps in determining when deeper infection is present but this can be difficult to assess clinically. Cobb et al showed slower resolution of lesions affecting the head and neck compared to lesions affecting other areas of the body and suggested that deeper infection is more frequently present in lesions affecting these areas, as previously reported by Reinke et al2,4.
Clipping of the hair in skin fold infections is indicated in long-haired breeds to remove matted fur that traps debris to the skin surface and impairs ventilation. In short-coated breeds, clipping can cause a sharp stubble that traumatises the skin on the opposing side of the fold, causing irritation. As in pyotraumatic dermatitis, cleaning of the skin is essential and the same type of topical antimicrobial products can be used for treatment of bacterial infection. Yeast infection with Malassezia pachydermatis is also frequently seen in intertrigo, either alone or in combination with bacterial infection, and for these cases preparations with additional antifungal efficacy should be selected. A 2% miconazole and 2% chlorhexidine shampoo (Malaseb, Dechra) is often effective if the owners can bathe the lesional area. The most effective way of treating intertrigo is by removal or reduction of affected skin folds. Weight reduction can be important, and surgery needs to be considered in severe, relapsing cases.
Treatment of surface pyoderma is based on addressing the underlying cause, establishment of ventilation, antimicrobials to address the microbial component of the disease and sometimes glucocorticoids to reduce pruritus and self-trauma. In difficult cases of intertrigo, surgical removal of the folds might be necessary, but many cases respond to topical treatment and subsequent preventive measures. Topical antibiotic and glucocorticoid preparations have been shown to be more effective as treatment for pyotraumatic dermatitis than either component given alone, justifying the use of such topical combinations in this disease5.
This article was kindly provided by Dechra Veterinary Products, makers of Fuciderm Gel.
1. Scott, D. W., Griffin, C. E., Miller, W. H. (2000) Muller and Kirk’s Small Animal Dermatology. 6th ed. Philadelphia: W. B. Saunders.
2. Reinke, S. I., Stannard, A. A., Ihrke, P. J. and Reinke, J. D. (1987) Histopathologic features of pyotraumatic dermatitis. J Am Vet Med Assoc 190 (1): 57-60.
3. Holm, B. R., Rest, J. R. and Seewald, W. (2004) A prospective study of the clinical findings, treatment and histopathology of 44 cases of pyotraumatic dermatitis. Veterinary Dermatology 15 (6): 369-376.
4. Cobb, M. A., Edwards, H. J., Jagger, T. D, et al. (2005) Topical fusidic acid/betamethasone-containing gel compared to systemic therapy in the treatment of canine acute moist dermatitis. Vet J 169 (2): 276-280.
5. Schroeder, H., Swan, G. E., Berry, W. L. and Pearson, J. (1996) Efficacy of a topical antimicrobial anti-inflammatory combination in the treatment of pyotraumatic dermatitis in dogs. Veterinary Dermatology 7 (3): 163-170.