Pyoderma

Surface pyoderma shows as redness, exudation and hair loss, as in hot spots and skin-fold dermatitis. Superficial pyoderma in dogs produces follicular papules and pustules, epidermal collarettes, crusts and patchy hair loss, most often on the trunk and underside; cats show crusted papules (miliary dermatitis) or eosinophilic plaques. Deep pyoderma is painful and smelly, with haemorrhagic crusts, ulcers, nodules, blood-stained or purulent discharge and draining tracts, commonly on the muzzle, chin, elbows, hocks and between the toes.

Pyoderma means a bacterial skin infection. In dogs, Staphylococcus pseudintermedius is the staphylococcus in more than 90% of superficial pyoderma and about 60% of deep pyoderma, with S. aureus and S. coagulans making up most of the rest; in cats S. aureus and S. pseudintermedius are the usual staphylococci. Dogs normally carry staphylococci on the skin without disease, and infection develops only when an underlying problem damages the skin barrier, so pyoderma is always secondary. Depth defines the disease: surface pyoderma involves only the upper epidermis, superficial pyoderma the epidermis and hair follicles, and deep pyoderma breaks through the follicle into the dermis and subcutis, where streptococci, Gram-negative bacteria and anaerobes are found in around 40% of cases.

Pyoderma is common in dogs, and superficial bacterial pyoderma is the most frequent reason dogs receive antimicrobials; it is uncommon in cats, where it tends to accompany allergies, parasites or chin acne. The underlying triggers include allergic disease (atopic dermatitis, food reactions, flea allergy), ectoparasites (sarcoptic mange, demodicosis, cheyletiellosis), endocrine disease such as hypothyroidism and hyperadrenocorticism, keratinisation disorders, dermatophytosis, skin folds, friction and trauma. Meticillin-resistant staphylococci (MRSP, MRSA) are a concern, especially after repeated antibiotic courses, and MRSA or other potentially zoonotic organisms in deep lesions call for precautions when sampling.

Dermatophytosis is ruled out with Wood's lamp examination and fungal culture or PCR, and demodicosis with skin scrapings and hair plucks; both can also underlie pyoderma. Pemphigus foliaceus forms sterile, immune-mediated pustules. Malassezia dermatitis, cheyletiellosis, mucocutaneous lupus erythematosus and leishmaniosis are also considered. Cytology showing neutrophils with intracellular cocci supports bacterial pyoderma.

Skin (epidermis, hair follicles, dermis, subcutis), skin folds, muzzle, chin, elbows, hocks, interdigital spaces, trunk and ventral abdomen

Identify and control the underlying cause (allergy, parasites, endocrine disease, skin folds); prefer topical antiseptics, reserving systemic antibiotics chosen by culture; proactive topical antiseptic therapy when the cause cannot be resolved.

Surface pyoderma should resolve in 7-14 days with topical care; superficial and deep forms need longer and rechecks. Recurrence is common when the underlying cause is missed, treatment is too short, or the drug is wrong.