Introduction

• Cause: inflammation of subcutaneous fat.
• Signs: sinus tracts, nodules and fistulae.
• Diagnosis: history, signs, histopathology.
• Treatment: surgery, antibiosis, immunosuppressive glucocorticoids, vitamin E.
• Prognosis: varies according to cause.

Pathogenesis

Etiology

• Focal ischemia:
  • Trauma, eg road traffic accident, surgery, especially abdominal.
  • Vasculitis.
  • Pressure.
• Infection:
  • Mycobacteria.
  • Proteus.
  • Nocardia.
  • Fungal infection.
• Immune-mediated disease:
  • Systemic lupus erythematosus Systemic lupus erythematosus.
  • Drug eruptions Skin: toxic epidermal necrolysis.
  • Neoplasia related, eg secondary to pancreatic adenocarcinoma Skin: 'idiopathic' furunculosis (German Shepherd Dog).
• Idiopathic.
• 
  Nutritional
• Vitamin E deficiency.

Predisposing factors

• May develop after subcutaneous injection.
• May develop <7 days following surgery.

Pathophysiology

• Inflammation of subcutaneous fat.
• Damage to fat cells releases lipid into extracellular space.
• Lipid is converted to fatty acids and these are potent inducers of inflammation.
• Granulomatous reactions to fatty acids develop.
• Can be sterile or associated with infection.

Timecourse

• Weeks.

Diagnosis

Treatment

Outcomes