Chapter 38 Pyoderma
Pyoderma refers to any pyogenic infection of the skin and is most commonly used in reference to bacterial skin infections. However, fungal organisms (especially yeast) have also been recognized as potentially significant opportunists in the development of surface pyoderma in the dog (see Chapter 41). Pyoderma is a common problem in clinical practice.
• Primary pyoderma refers to a skin infection that does not recur after the appropriate treatment. These infections are most likely the result of a transient and non-recurrent insult to the skin.
• Secondary pyodermas are far more common and are associated with a persistent or recurrent underlying problem that alters the skin’s resistance to infection. Until the underlying problem is identified and corrected, the infection usually responds only temporarily to therapy and subsequently recurs.
• Pyodermas are caused by bacterial colonization or invasion of the skin by coagulase-positive staphylococci, usually Staphylococcus intermedius. In chronic, recurrent, or deep pyodermas, secondary bacterial invaders may also be present, especially Pseudomonas spp., Proteus spp., and Escherichia coli. When deep pyoderma occurs, anaerobic bacteria such as Bacteroides spp., Peptostreptococcus spp., Fusobacterium spp., Porphyromonas spp., and Clostridium spp. may be further opportunistic pathogens. Recently, two additional staphylococci have been isolated from cases of recurrent pyodermas, namely Staphylococcus schleiferi subsp schleiferi and Staphylococcus schleiferi subsp coagulans, both of which are frequently methicillin-resistant staphylococci.
SURFACE PYODERMAS
Acute Moist Dermatitis (Hot Spot) (Pyotraumatic Dermatitis)
Etiology
Self-trauma to the skin, due to an underlying pruritic or painful process, can result in a focal surface pyoderma referred to as acute moist dermatitis. Underlying conditions that may be associated with the development of acute moist dermatitis are listed in Table 38-1.
Table 38-1 CONDITIONS ASSOCIATED WITH HOT SPOTS
| Disease Category | Examples |
|---|---|
| Allergic skin diseases | Flea allergy dermatitis |
| Atopic dermatitis (atopy) | |
| Cutaneous adverse food reactions (food allergy) | |
| Allergic contact dermatitis | |
| Secondary staphylococcal hypersensitivity | |
| Ectoparasites | Canine scabies |
| Cheyletiellosis | |
| Demodicosis | |
| Otitis externa | Allergic otitis externa |
| Ceruminous otitis externa | |
| Environmental causes | Irritant contact dermatitis |
| Poor grooming | |
| Burs or plant awns in the skin or haircoat | |
| Musculoskeletal disorders | Hip dysplasia |
| Degenerative joint disease | |
| Arthritis and other arthropathies | |
| Anal sac problems | Impacted anal sacs |
| Anal sacculitis |
From Rosser EJ, Sams A: Pruritus. In Allen DG (ed): Small Animal Medicine. Philadelphia: JB Lippincott, 1991, p 704.
Clinical Signs
• Acute moist dermatitis is usually a single alopecic lesion that is circumscribed, erythematous, thickened, and erosive. An exudative film occurs over the surface, and peripheral hairs are matted onto the lesion. The lesion develops subsequent to the dog’s chewing and licking at a focal area of pruritus or pain, and it develops within a matter of hours. The lesion is usually painful.
• Lesions that appear clinically similar to an acute moist dermatitis (pyotraumatic dermatitis), but develop in the absence of a history of self-trauma, are often associated with a deeper bacterial folliculitis and/or furunculosis and are most commonly observed on the side of the face, or cheek region (also referred to as pyotraumatic folliculitis). The breeds more commonly affected by this deeper form of an acute moist dermatitis are golden retrievers, Saint Bernards, Bouviers, and Newfoundlands. In these cases, satellite popular lesions can usually be detected surrounding the area of acute moist dermatitis once the area has been clipped.
Diagnosis
• History includes questioning the owner about any pruritic skin disease, painful process, or environmental irritant that might indicate the reason for the dog’s self-trauma of the area (see Table 38-1). In instances of recurrent acute moist dermatitis, identify the underlying problem to prevent any further recurrences.
• Biopsy lesions that appear clinically similar to an acute moist dermatitis, that develop in the absence of a history of self-trauma, and that respond poorly or are non-responsive to initial treatment. This is to determine if the lesion is associated with a deeper bacterial folliculitis and/or furunculosis, which requires a more aggressive treatment regimen.
Treatment
Topical Therapy
• First gently clip and thoroughly cleanse the area with an antiseptic shampoo, such as povidone-iodine (Betadine, Purdue Frederick) or chlorhexidine (Hexadene, Allerderm/Virbac; ChlorhexiDerm, DVM Pharmaceuticals). Because the lesion is often very painful, this step may require sedation or general anesthesia.
• Dry the lesion by applying an astringent, such as Burow’s solution (Domeboro powder and water; Bayer) or hamamelis extract (DermaCool with Lidocaine, Allerderm/Virbac), and then apply a nystatin-neomycin sulfate-thiostrepton-triamcinolone acetonide cream (Panalog Cream, Fort Dodge; Animax Cream, Pharmaderm; Dermagen Cream, Butler). Repeat these treatments q12h, for 5 to 10 days.
Systemic Therapy
• Corticosteroids are indicated in the treatment of hot spots because the lesion is often painful or pruritic and because the most common underlying causes are allergic skin diseases. Begin treatment with a short-acting, injectable corticosteroid. Since prednisolone and prednisone are no longer available in non-repositol injectable forms, dexamethasone solution—2 mg/ml (Aspen) at 0.05 mg/kg IM (not to exceed 1 mg/dog)—may be given for a rapid anti-inflammatory and anti-pruritic effect. The next day administer oral prednisolone or prednisone at 0.5 mg/kg q12h for 5 to 7 days, then 0.5 mg/kg q24h for the next 5 to 7 days.
Skin Fold Pyoderma
Etiology
• Deep skin folds, where the skin rubs against itself and causes irritation and maceration, can result in a surface pyoderma referred to as a skin fold pyoderma (intertrigo). These skin folds create a moist, dark, and warm environment with poor air circulation, which retains skin secretions and desquamated keratinocytes that promotes subsequent bacterial (S. intermedius) or yeast (Malassezia pachydermatis) overgrowth and inflammation.
• Pyoderma can occur in any skin fold in any breed of dog, but intertrigo is most commonly associated with the skin folds in certain breeds of dogs. Table 38-2 lists the anatomic sites of the more common skin fold pyodermas and their breed predispositions, and it includes lip fold, facial fold, vulvar fold, tail fold, body fold, and leg fold pyodermas.
Table 38-2 SKIN FOLD PYODERMAS
| Anatomic Site | Breed Predisposition | Comments |
|---|---|---|
| Lip fold | Cocker spaniel | Lower lip fold, halitosis |
| Springer spaniel | ||
| Saint Bernard | ||
| Irish setter | ||
| Facial fold | Brachycephalic types | Between nose and eyes |
| Shar-Pei | Lateral facial region | |
| Body fold | Shar-Pei | Also any breed with pendulous mammary glands, obese patients |
| Vulvar fold | None | Obese females, juvenile vulva, spayed early in life |
| Leg fold | Chondrodystrophic types (basset hound, dachshund) | Obese patients |
| Tail fold | Bulldog | “Corkscrew tails,” anal odor |
| Boston terrier | ||
| Pug |
Clinical Signs
• Skin fold pyoderma is characterized by inflammation and mild exudation. This pyoderma is best identified by simply widening the skin fold. The area is often malodorous.
Diagnosis
• Direct impression skin cytology: Press a clean glass microscope slide over the exudative area, and then gently heat fix and stain with Diff-Quik (Dade Behring). Examine microscopically under oil immersion (1000×) to best identify and quantitate the presence of cocci versus rods versus yeast type of opportunistic organisms (see Chapter 37). This will aid in the selection of the most appropriate active ingredient in your topical therapy, especially in chronic, recurrent cases.
Treatment
• First gently expose and cleanse the skin fold with a benzoyl peroxide shampoo (OxyDex Shampoo, DVM Pharmaceuticals; Pyoben Shampoo, Allerderm/Virbac; Benzoyl-Plus, EVSCO Pharmaceuticals).
• Dry the area manually and apply a topical mild astringent, such as Burow’s solution (Domeboro powder and water; Bayer).
• When only bacteria are found on direct impression skin cytology, follow with a twice-daily application of a benzoyl peroxide-containing gel (OxyDex Gel, DVM Pharmaceuticals; Pyoben Gel, Allerderm/Virbac) into the skin fold region for 10 to 14 days. When only yeast organisms or both bacteria and yeast organisms are found on direct impression skin cytology, follow with a twice-daily application of a miconazole- and chlorhexidine-containing preparation (Malaseb Pledgets, DVM Pharmaceuticals) into the skin fold region for 10 to 14 days.
• In cases involving a more severe inflammatory response, treat for the first 2 to 3 days with twice-daily applications of a nystatin-neomycin sulfate-thiostrepton-triamcinolone acetonide cream (Panalog Cream, Fort Dodge; Animax Cream, Pharmaderm; Dermagen Cream, Butler) into the skin fold region. Once the inflammation has subsided, institute the benzoyl peroxide or miconazole and chlorhexidine preparation.
SUPERFICIAL PYODERMAS
• Superficial pyoderma is a bacterial invasion of the epidermis that can manifest itself in one of two ways. First, the bacteria can penetrate the stratum corneum with the subsequent formation of subcorneal pustules and is referred to as impetigo (puppy pyoderma). Second, the bacteria can invade the opening of the hair follicle causing inflammation and is referred to as folliculitis.
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