Pyoderma

Etiology

• Pyoderma in dogs and cats is most commonly caused by an overgrowth of resident or transient bacteria that normally colonize the skin. In dogs, the primary pathogen is Staphylococcus pseudo-intermedius, which can overgrow and become pathogenic under certain conditions.​

• In cats, the primary bacterial cause of pyoderma is typically Staphylococcus spp., although other bacteria can play a role as secondary pathogens.​

• Pyoderma can be classified based on the depth of infection:

  • Surface pyoderma includes conditions like:

    • Acute moist dermatitis (hot spots)

    • Fold pyoderma (intertrigo)

    • Bacterial overgrowth syndrome

  • Superficial pyoderma (bacterial folliculitis) extends into the hair follicle and epidermis.

  • Deep pyoderma is more serious, extending into the dermis, and carries a higher risk of bacteremia.

• The risk of superficial pyoderma is greatly influenced by bacterial adherence to keratinocytes, particularly in warm, moist areas of the skin such as:

  • Lip folds

  • Facial folds

  • Axillary areas

  • Interdigital areas

  • Tail folds

  • Pressure points like elbows and hocks

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Clinical Findings

• In Dogs:

  • Superficial pyoderma often presents with:

    The trunk and ventrum are the most commonly affected areas.

    • Multifocal alopecia

    • Follicular papules or pustules

    • Epidermal collarettes

    • Crusts and scales

  • Deep pyoderma (more serious and less common) presents with:

    Other manifestations of deep pyoderma include acral lick granulomas and pyotraumatic dermatitis.

    • Pain

    • Crusting

    • Odor

    • Exudation of blood and pus

    • Erythema, swelling, ulcerations, hemorrhagic crusts, and draining tracts

    • Areas such as the bridge of the muzzle, chin, elbows, hocks, and interdigital areas are more prone to deep infections.

• In Cats:

  • Superficial pyoderma is less common but often seen in allergic skin diseases or conditions like feline chin acne. Miliary dermatitis can be a clinical manifestation.

  • Deep pyoderma in cats presents with:

    Recurrent or non-healing deep pyoderma may indicate underlying systemic diseases like feline immunodeficiency virus (FIV), feline leukemia virus (FeLV), or atypical mycobacteria.

    • Alopecia

    • Ulcerations

    • Hemorrhagic crusts

    • Draining tracts

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Diagnosis 

• Diagnosis is made through clinical signs, bacterial culture, and ruling out other causes of folliculitis (e.g., demodicosis or dermatophytosis). Key diagnostic techniques include:

  • Skin cytology: Valuable for identifying inflammatory cells and bacteria. It is often used to detect Malassezia dermatitis as a concurrent infection.

  • Bacterial culture and susceptibility testing: Essential in cases of recurrent pyoderma, deep pyoderma, or infections with resistant organisms (e.g., methicillin-resistant Staphylococcus).

  • Wood’s lamp examination: Used to rule out dermatophytosis.

  • Skin scrapings: Deep scrapings can help rule out follicular demodicosis.

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Treatment

• Effective treatment of pyoderma depends on identifying and managing the underlying cause. Key aspects include:

  • Empirical antibiotic therapy is often initiated, but bacterial culture and susceptibility testing are critical for recurrent or resistant infections.

  • Topical therapy (e.g., shampoos, creams, gels, and ointments) can be effective for mild or localized cases of superficial pyoderma and can be used adjunctively for deep pyoderma. Common active ingredients include:

    • Chlorhexidine (2%–4%): Bactericidal by disrupting bacterial membranes.

    • Benzoyl peroxide (2.5%–3%): An oxidizing agent that ruptures bacterial cell membranes.

    • Ethyl lactate (10%): Both bactericidal and bacteriostatic.

    • Sodium hypochlorite (0.005%): Anti-inflammatory and effective against both Gram-negative and Gram-positive bacteria.

• For systemic therapy, first- and second-tier antibiotics are used:

  • First-tier drugs (empirically used if no history of MRSA):

    • Clindamycin

    • First-generation cephalosporins

    • Amoxicillin-clavulanate

    • Potentiated sulfonamides

  • Second-tier drugs (used based on bacterial culture and sensitivity):

    • Fluoroquinolones (e.g., ciprofloxacin)

• Duration of therapy should extend at least 7–10 days beyond clinical resolution for superficial pyoderma and 14–20 days for deep pyoderma.

• Immunomodulators (such as bacterins) may be considered for recurrent cases, although their exact mechanism of action is unclear. They are used in conjunction with initial antimicrobial therapy for the first 4–6 weeks.

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Underlying Causes of Recurrent Pyoderma

• Recurrent pyoderma is often due to failure to identify and manage underlying causes, including:

  • Allergies (e.g., atopic dermatitis, flea allergy, food allergy)

  • Endocrinopathies (e.g., hypothyroidism, hyperadrenocorticism)

  • Keratinization disorders

  • Follicular dysplasias

  • Ectoparasites

  • Poor grooming or hygiene

• Identifying and addressing these triggers is essential to prevent recurrence.

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