Actinomycosis

Actinomycosis is a chronic suppurative granulomatous infection caused by Actinomyces species (mainly A. israelii), anaerobic or microaerophilic Gram positive filamentous bacteria that are normal oral and gastrointestinal commensals.

• Infection follows disruption of mucosal barriers: dental infection or extraction (cervicofacial), aspiration (thoracic), abdominal surgery, appendicitis, and intrauterine contraceptive device use (pelvic).
• Occurs at any age, men more often than women (except pelvic disease).
• Risk factors: poor dental hygiene, diabetes, alcoholism, immunosuppression, bisphosphonate related jaw osteonecrosis, and radiotherapy.

• Cervicofacial ("lumpy jaw", 50%): painless, firm, indurated swelling at the angle of the mandible, then abscess and draining sinus tracts with yellow "sulphur granules".
• Thoracic (15 to 20%): cough, fever, chest pain, and haemoptysis; consolidation or mass mimicking cancer or TB, with extension through the chest wall (empyema necessitans).
• Abdominopelvic (20%): mass in the ileocaecal region or pelvis (with IUD), fistulae, and abscesses.
• CNS (brain abscess) and disseminated forms are rare.

• Microscopy of pus: sulphur granules with Gram positive branching filaments; culture under anaerobic conditions (hold for 14 days), and 16S rRNA PCR.
• Histology: filamentous organisms, granulomas, neutrophils, and fibrosis.
• CT or MRI for extent; biopsy to exclude malignancy.
• Exclude nocardiosis, tuberculosis, malignancy, mycetoma, fungal infection, and Crohn disease.

• Prolonged antibiotics: penicillin G 18 to 24 million units per day IV in divided doses (or ampicillin 50 mg/kg every 6 hours) for 2 to 6 weeks, followed by oral penicillin V 2 to 4 g per day or amoxicillin 500 mg to 1 g three times daily for 6 to 12 months (shorter, 3 to 6 months, for uncomplicated cervicofacial disease).
• Alternatives: doxycycline 100 mg twice daily, ceftriaxone 2 g daily, clindamycin 600 mg every 8 hours, and erythromycin.
• Surgical drainage and debridement of abscesses, sinus tracts, and necrotic tissue; removal of intrauterine device in pelvic disease.
• Dental care and eradication of local sources.
• Monitor with imaging for resolution; relapse is common after short courses.