Features

Pyotraumatic dermatitis is an acute and rapidly developing surface bacterial skin infection that occurs secondary to self-inflicted trauma. A lesion is created when the patient licks, chews, scratches, or rubs a focal area on its body in response to a pruritic or painful stimulus (Box 3-1). This usually is a seasonal problem that becomes more common when the weather is hot and humid. Fleas are the most common initiating stimulus. Pyotraumatic dermatitis is common in dogs, especially in thick-coated, long-haired breeds. It is rarely seen in cats.

BOX 3-1

Causes of Pyotraumatic Dermatitis

Fleas

Other parasites (e.g., pediculosis, cheyletiellosis, scabies)

Hypersensitivity (e.g., atopy, food, flea bite)

Anal sac disease

Otitis externa

Folliculitis (e.g., bacterial, Demodex sp., dermatophytic)

Trauma (e.g., minor wounds, foreign body)

Contact dermatitis

Pyotraumatic dermatitis is an acutely pruritic, rapidly enlarging area of erythema, alopecia, and weepy, eroded skin with well-demarcated margins. Lesions are usually single, but they may be multiple and often are painful. They occur most frequently on the trunk, tail base, lateral thigh, neck, and face. A spreading superficial pyoderma is often present.

Top Differentials

Differentials include superficial pyoderma, demodicosis, and dermatophytosis.

Diagnosis

Treatment and Prognosis

BOX 3-2

Antibiotics for Bacterial Skin Infection*

Antibiotic and Dose

First-Line Drugs

Cefadroxil 22 mg/kg q 8–12 hours

Cefpodoxime 5–10 mg/kg q 12–24 hours

Cefovecin sodium (Convenia) 8 mg/kg SQ

Cephalexin 22 mg/kg q 8 hours, or 30 mg/kg q 12 hours

Cephradine 22 mg/kg q 8 hours

Clavulanated amoxicillin 12.5 mg/kg q 8 hours or 22 mg/kg q 12 hours

Ormetoprim/sulfadimethoxine (Primor) 55 mg/kg once on day 1, then 27.5 mg/kg q 24 hours

Oxacillin 22 mg/kg q 8 hours

Trimethoprim/sulfadiazine 22–30 mg/kg q 12 hours

Second-Line Drugs

Chloramphenicol 30–50 mg/kg q 8 hours

Clindamycin hydrochloride 11 mg/kg q 12 hours

Erythromycin 10–15 mg/kg q 8 hours

^* Antibiotics in bold are the author’s preferred selections because of improved owner compliance.

Author’s Note

FIGURE 3-1 Pyotraumatic Dermatitis.

This moist, erosive lesion on the base of the ear is characteristic of a hot spot.

FIGURE 3-2 Pyotraumatic Dermatitis.

Close-up of the dog in Figure 3-1. The moist, erosive surface of the lesion is apparent. The papular perimeter suggests an expanding superficial pyoderma.

FIGURE 3-3 Pyotraumatic Dermatitis.

Close-up of a hot spot demonstrating the erosive lesion with a moist serous exudate.

FIGURE 3-4 Pyotraumatic Dermatitis.

An early superficial lesion (after clipping) on the lumbar region of a dog with flea allergy dermatitis. The papular perimeter suggests an expanding bacterial folliculitis.

FIGURE 3-5 Pyotraumatic Dermatitis.

This moist lesion developed acutely on the dorsum of this flea-allergic cat.

FIGURE 3-6 Pyotraumatic Dermatitis.

A severe erosive lesion with exudate on the ventral neck of a food-allergic cat.

Features

Impetigo is a superficial bacterial infection of nonhaired skin that may be associated with a predisposing disease or other underlying factors, such as endoparasitism, ectoparasitism, poor nutrition, or a dirty environment. It is commonly seen in young dogs before the time of puberty.

Impetigo is characterized by small, nonfollicular pustules, papules, and crusts that are limited to the inguinal and axillary skin. Lesions are not painful or pruritic.

Top Differentials

Differentials include demodicosis, superficial pyoderma, dermatophytosis, insect bites, and early scabies.

Diagnosis

Treatment and Prognosis

FIGURE 3-7 Impetigo.

Numerous superficial pustules and crusts on the abdomen of this puppy are typical of this disease.

FIGURE 3-8 Impetigo.

More chronic lesions demonstrated by hyperpigmented macules on the abdomen of a puppy. Note that the papular dermatitis is still apparent.

Features

Superficial pyoderma is a superficial bacterial infection involving hair follicles and the adjacent epidermis. The infection is almost always secondary to an underlying cause; allergies and endocrine disease are the most common causes (Box 3-3). Superficial pyoderma is one of the most common skin diseases in dogs but is rare in cats.

BOX 3-3

Causes of Secondary Superficial and Deep Pyoderma

Demodicosis, scabies, Pelodera

Hypersensitivity (e.g., atopy, food, flea bite)

Endocrinopathy (e.g., hypothyroidism, hyperadrenocorticism, sex hormone imbalance)

Immunosuppressive therapy (e.g., glucocorticoids, progestational compounds, cytotoxic drugs)

Autoimmune and immune-mediated disorders

Trauma or bite wound

Other skin diseases

Superficial pyoderma is characterized by focal, multifocal, or generalized areas of papules, pustules, crusts and scales, or epidermal collarettes, or circumscribed areas of erythema and alopecia, that may have hyperpigmented centers. Short-coated dogs often present with a “moth-eaten” patchy alopecia, small tufts of hair that stand up, or reddish brown discoloration of white hairs. In long-coated dogs, symptoms can be insidious and may include a dull, lusterless hair coat, scales, and excessive shedding. In both short- and long-coated breeds, primary skin lesions are often obscured by remaining hairs but can be readily appreciated if an affected area is clipped. Pruritus is variable, ranging from none to intense levels. Bacterial infection secondary to endocrine disease may cause pruritus, thereby mimicking allergic skin disease.

Staphylococcus pseudintermedius (previously Staphylococcus intermedius) is the most common bacterium isolated from canine pyoderma and is usually limited to dogs. Staphylococcus schleiferi is a bacterial species in dogs and humans that is emerging as a common canine isolate in patients with chronic infection and previous antibiotic exposure. Both S. pseudintermedius and S. schleiferi may develop methicillin resistance, especially if subtherapeutic doses of antibiotics or fluoroquinilone antibiotics have been used previously in the patient. Additionally, methicillin-resistant Staphylococcus aureus (human MRSA) is becoming more common among veterinary species. All three types of Staphylococcus may be zoonotic, moving from human to canine or from canine to human; immunosuppressed individuals are at greatest risk.

Top Differentials

Differentials include demodicosis, dermatophytosis, scabies, and autoimmune skin diseases.

Top Diagnosis

Top Treatment and Prognosis

Author’s Note

FIGURE 3-9 Superficial Pyoderma.

Alopecia, papules, and crusts around the eye of this allergic Irish setter are typical of bacterial folliculitis.

FIGURE 3-10 Superficial Pyoderma.

Papular rash on the abdomen of an allergic dog caused by multidrug-resistant Staphylococcus schleiferi. The papular rash typical of pyoderma persisted despite high-dose antibiotic therapy, suggesting the antibiotic-resistant nature of the organism.

FIGURE 3-11 Superficial Pyoderma.

Close-up of the papular rash in Figure 3-10.

FIGURE 3-12 Superficial Pyoderma.

This papular dermatitis forms coalescing lesions as demonstrated by the erythematous plaque. Note the early epidermal collarettes associated with some papules.

FIGURE 3-13 Superficial Pyoderma.

Severe erythematous dermatitis with large epidermal collarettes caused by a multidrug-resistant infection.

FIGURE 3-14 Superficial Pyoderma.

Close-up of the dog in Figure 3-13. Erythematous dermatitis with epidermal collarettes formation is apparent.

FIGURE 3-15 Superficial Pyoderma.

More typical epidermal collarettes in a dog with resolving pyoderma.

FIGURE 3-16 Superficial Pyoderma.

This moth-eaten texture of the hair coat is a characteristic finding in short-coated breeds with pyoderma.

FIGURE 3-17 Superficial Pyoderma.

The moth-eaten alopecia is typical of pyoderma in short-coated breeds.

FIGURE 3-18 Superficial Pyoderma.

Focal papules and crusts caused by pyoderma can be hidden by a dense fur coat. A window was clipped within the fur coat to reveal these lesions.

FIGURE 3-19 Superficial Pyoderma.

Large pustules within an erythematous papular rash are an uncommon lesion in association with pyoderma. Pustules are easily ruptured, making them difficult to find.

FIGURE 3-20 Superficial Pyoderma.

Large coalescing pustules in a dog with underlying hyperadrenocorticism. Cushing’s disease has altered the normal lesion development typically seen in pyoderma.

FIGURE 3-21 Superficial Pyoderma.

This large focal area of alopecia, erythema, and hyperpigmentation with central regrowth of hair is often misdiagnosed as dermatophytosis.

FIGURE 3-22 Superficial Pyoderma.

Partial alopecia and mild papular rash on the foreleg of this dog were caused by secondary bacterial folliculitis associated with hypothyroidism.

FIGURE 3-23 Superficial Pyoderma.

This focal area of lichenification with adherent crust formation on the upper lip of a dog responded to topical mupirocin therapy.

(Courtesy L. Frank.)

FIGURE 3-24 Superficial Pyoderma.

Alopecic dermatitis with a purulent exudate on the lip of a dog. Note how the dog’s normal pigmentation masks the papular dermatitis.

FIGURE 3-25 Superficial Pyoderma.

Crusting papular dermatitis caused matting of the hair in this medium-haired dog. In thick-coated breeds, it may be difficult to see the underlying cutaneous lesions.

FIGURE 3-26 Superficial Pyoderma.

Papular crusting dermatitis with alopecia on the muzzle of a dog.

FIGURE 3-27 Superficial Pyoderma.

Multifocal, punctate lesions on the dorsum are a typical feature of postbathing folliculitis and furunculosis.

FIGURE 3-28 Superficial Pyoderma.

Focal area of alopecia caused by folliculitis in an allergic dog. Cutaneous cytology is necessary.

FIGURE 3-29 Superficial Pyoderma.

Erythema caused by secondary infection in an allergic dog. The lesion is indistinguishable from a Demodex, dermatophyte, or yeast infection.

FIGURE 3-30 Superficial Pyoderma.

Multiple papules, crusts, and epidermal collarettes in a dog with hypothyroidism.

FIGURE 3-31 Superficial Pyoderma.

Close-up of the dog in Figure 3-30. Papular rash with crusting is apparent.

FIGURE 3-32 Superficial Pyoderma.

Severe papular rash with crusting dermatitis in an allergic dog.

FIGURE 3-33 Superficial Pyoderma.

An unusual pyoderma lesion on the head of a dog with allergies.

FIGURE 3-34 Superficial Pyoderma.

Severe erythematous dermatitis without the typical papular, crusting rash, which is more typical of pyoderma.

FIGURE 3-35 Superficial Pyoderma.

Same dog as in Figure 3-34. Erythematous macular lesions without a papular rash are apparent.

FIGURE 3-36 Superficial Pyoderma.

Same dog as in Figure 3-34. Erythematous macular lesions without a papular rash are apparent.

FIGURE 3-37 Superficial Pyoderma.

Atypically shaped erythematous lesions in an allergic dog. Cutaneous cytology identified cocci, and the patient responded to oral antibiotics administered for 3 weeks.

FIGURE 3-38 Superficial Pyoderma.

Generalized dermatitis in an allergic dog. The severe inflammation is similar to staphylococcal scalded skin syndrome in humans.

FIGURE 3-39 Superficial Pyoderma.

Mild erythema and crusting papules on the abdomen of a male dog. Cytology identified cocci and ruled out demodicosis.

FIGURE 3-40 Superficial Pyoderma.

Severe inflammation caused by secondary bacterial infection. Comedones and pustules are visible.

FIGURE 3-41 Superficial Pyoderma.

Papular rash and epidermal collarettes are classic lesions caused by folliculitis. Cutaneous cytology is necessary to determine whether the cause is a bacterium, Demodex, or a dermatophyte.

FIGURE 3-42 Superficial Pyoderma.

Papular rash with epidermal collarettes typical of folliculitis in an allergic dog.

Features

Deep pyoderma is a surface or follicular bacterial infection that breaks through hair follicles to produce furunculosis and cellulitis. Its development is often preceded by a history of chronic superficial skin disease, and it is almost always associated with some predisposing factor (see Box 3-3). Deep pyoderma is common in dogs and rare in cats.

Staphylococcus pseudintermedius (previously Staphylococcus intermedius) is the most common bacterium isolated from canine pyoderma and is usually limited to dogs. Staphylococcus schleiferi is a bacterial species in dogs and humans that is emerging as a common canine isolate in patients with chronic infection and previous antibiotic exposure. Both S. pseudintermedius and S. schleiferi may develop methicillin resistance, especially if subtherapeutic doses of antibiotics or fluoroquinilone antibiotics have been used previously in the patient. Additionally, methicillin-resistant Staphylococcus aureus (human MRSA) is becoming more common among veterinary species. All three types of Staphylococcus may be zoonotic, moving from human to canine or from canine to human; immunosuppressed individuals are at greatest risk.

Deep pyoderma manifests as focal, multifocal, or generalized skin lesions characterized by papules, pustules, cellulitis, tissue discoloration, alopecia, hemorrhagic bullae, erosions, ulcers, and crusts, as well as serosanguineous to purulent draining fistulous tracts. Lesions are often pruritic or painful. They most often involve the trunk and pressure points but can appear anywhere on the body. Lymphadenomegaly is common. If the animal is also septic, other symptoms include fever, anorexia, and depression.

Top Differentials

Differentials include demodicosis, fungal infection, actinomycosis, nocardiosis, mycobacteriosis, neoplasia, and autoimmune skin disorders.

Diagnosis

Treatment and Prognosis

FIGURE 3-43 Deep Pyoderma.

Purulent exudate from a deep ulcerative lesion and draining tract.

FIGURE 3-44 Deep Pyoderma.

Patchy alopecia with focal crusted lesions covering ulcers and draining tracts. Note that deep pyoderma (cellulitis) affects a large region of skin, rather than discrete papules or pustules typical of superficial pyoderma.

FIGURE 3-45 Deep Pyoderma.

This focal area of alopecia and lichenification demonstrates an ulcer and draining tract typical of deep pyoderma. Note that lichenification is caused by the chronicity of the lesion.

FIGURE 3-46 Deep Pyoderma.

This aggressive bacterial infection was causing necrosis of large sections of skin, suggestive of necrotizing fasciitis. Numerous bacterial species, including methicillin-resistant Staphylococcus aureus, were isolated on culture.

FIGURE 3-47 Deep Pyoderma.

Diffuse erythematous dermatitis of the foot. The medial digit is the site of previous surgery; it subsequently became infected with Pseudomonas. Note that dermatitis of surrounding tissue is caused by opportunistic infection at the surgical site.

FIGURE 3-48 Deep Pyoderma.

Severe interdigital dermatitis (alopecia, erythema, lichenification) with a moist exudate and draining tract typical of deep pyoderma.

Features

Chin pyoderma is a bacterial infection that is not true acne, but rather is a traumatic furunculosis. Short, stiff hairs are forced backward through the hair follicle, creating a sterile foreign body reaction that may become subsequently infected. This may be induced by trauma to the chin (e.g., caused by lying on hard floors, friction from chew toys). Chin pyoderma is common in short-coated breed dogs, especially when young (3- to 12-month-old).

Chin pyoderma manifests as nonpainful and nonpruritic comedones, papules, pustules, and bullae, or as ulcerative draining tracts with serosanguineous discharge, on the chin or muzzle. Often hair can be expressed from the lesions when gently squeezed.

Top Differentials

Differentials include demodicosis, dermatophytosis, early juvenile cellulitis, and contact dermatitis.