Actinomycosis

Organism

• Caused by Actinomyces israelii (most commonly)
• Gram-positive, filamentous, non–acid-fast anaerobic bacteria
• Commensal in the oral cavity, gastrointestinal tract, and female genital tract
• Becomes pathogenic when mucosal barriers are breached (e.g. surgery, trauma, perforation)

Pathophysiology

• Requires devitalised or hypoxic tissue and anaerobic conditions to establish infection
• Leads to chronic, indolent infection characterised by:
  • Granulomatous inflammation
  • Dense fibrosis and induration
  • Multiple abscesses and sinus tract formation
• Produces characteristic “sulphur granules”
  • Yellowish microcolonies of organisms seen in pus or tissue

Common surgical sites and mimics

• Cervicofacial (50–60%)
  • “Lumpy jaw” — often post-dental procedures or trauma
• Thoracic
  • Pulmonary or chest wall masses, may mimic malignancy or TB
• Abdominal and pelvic (15–20%)
  • Mimics malignancy, Crohn’s disease, diverticulitis, tubo-ovarian abscess
  • Often follows perforated appendicitis, bowel surgery, or IUD use

Clinical features

• Chronic indurated mass with multiple discharging sinuses
• Minimal systemic toxicity despite extensive disease
• May cross tissue planes and anatomical boundaries
• Intraoperatively may appear as dense fibrotic mass with abscesses or sinuses

Diagnosis

• Clinical suspicion important due to non-specific imaging and slow growth
• Imaging may show mass-like lesion, abscesses, fistulae, or sinus tracts
• Sulphur granules in pus (seen on microscopy)
• Culture of aspirates/tissue (requires prolonged anaerobic incubation)
• Histopathology: filamentous bacteria in granules within inflammatory tissue

Treatment

• High-dose penicillin or amoxicillin for prolonged duration (6–12 months)
  • Alternatives: doxycycline, clindamycin if penicillin-allergic
• Surgical drainage or debridement may be required
  • Especially for large abscesses, sinuses, or to exclude malignancy
• IUD removal if pelvic actinomycosis suspected

Prognosis

• Excellent with prolonged antibiotic therapy and surgical control if needed
• Recurrence possible with incomplete treatment or poor source control