Deep Pyoderma

• Less common than superficial pyoderma
• Occurs mainly in dogs
• Affects infundibulum, isthmic portion of hair follicles and surrounding dermis and subcutis
• Heals with scarring
• Local lymph nodes are often affected
• Often secondary to immunosuppression, follicular hyperkeratosis or demodicosis
• May also be a sequele to superficial pyoderma
• Grossly:
  • Crusted papules, pustules, alopecia, abscesses, nodules, fistulas, ulcers, haemorrhagic bullae
  • In dogs may look similar to pyotraumatic dermatitis
• Microscopically:
  • Pyogranulomatous folliculitis and furunculosis
  • Nodular or diffuse dermatitis
  • Panniculitis
• May involve a foreign bodey reaction to follicular contents and draining sinuses develop
• If chronic, scarring and loss of adnexa
• Bacteria often isolated include Staphylococcus spp., especially S. intermedius in dogs, Streptococcus spp., Corynebacterium pseudotuberculosis, Pseudomonas, Pasteurella, Proteus, E.coli

Subcutaneous Abscesses

• Purulent exudate within dermis and subcutis
• Commonly occurs in cats due to contamination of penetrating wounds
• Surrounding wall of collagen and fibroblasts may develop
• Common bacteria (often normal mouth flora)
  • Pasteurella multocida, Fusobacterium spp., beta - haemolytic streptococci, Bacteroides