Abdominal Actinomycosis

Abdominal actinomycosis is a chronic suppurative infection caused by Actinomyces species, usually Actinomyces israelii, which are Gram-positive, filamentous, non-spore-forming anaerobes that live as commensals in the mouth, colon and female genital tract. Infection follows loss of mucosal integrity.

Abdominal disease accounts for about 20% of all actinomycosis (cervicofacial is the most common form, with thoracic disease next).

Predisposing factors

• Perforated or gangrenous appendicitis, diverticulitis and bowel perforation

• Abdominal surgery and trauma

• An intrauterine contraceptive device in place for over 5 years (pelvic disease)

• Immunosuppression, diabetes, poor dental hygiene and malignancy

The organism forms sulfur granules (clumps of filaments in a matrix) in abscesses. The disease is slowly progressive, crosses tissue planes, forms sinuses to the skin and invades the abdominal wall. It is often mistaken for malignancy (hence the term "great mimicker").

The ileocecal region and appendix are the usual sites.

Complications: abdominal wall fistulae, hepatic abscess (by portal spread), psoas abscess, bowel obstruction, and recurrence after incomplete therapy.

• Insidious abdominal pain, a firm and fixed mass (often in the right iliac fossa), low-grade fever, weight loss and malaise over weeks to months

• Chronic draining sinuses on the abdominal wall releasing sulfur granules

• Prior surgery, appendicitis or IUD use

• Pelvic disease: pelvic mass, vaginal discharge, and unilateral adnexal tenderness with an IUD

• Hepatic involvement: fever, right upper quadrant pain and raised alkaline phosphatase

• CT with intravenous contrast: an infiltrative soft tissue mass with enhancing walls and central low-attenuation areas, spread across tissue planes into the abdominal wall, little lymphadenopathy, and fistulae.

• Anaerobic culture of pus or tissue, held for 14 days (inform the laboratory). Cultures are positive in only about 25 to 50%, and prior antibiotics reduce yield.

• Histology with Gram and Grocott stains: sulfur granules with club-like filaments at the periphery and a surrounding neutrophil rim.

• 16S ribosomal RNA PCR on tissue to improve detection.

• Colonoscopy and tissue biopsy to exclude Crohn disease and carcinoma, and a cervical or IUD culture for pelvic disease.

Prolonged antibiotics are the core of treatment. Surgery treats abscess and fistula.

Intravenous induction

• Benzylpenicillin 18 to 24 million units a day IV in divided doses every 4 hours (or by continuous infusion) for 2 to 6 weeks, until clinical response.
• Children: benzylpenicillin 200,000 to 300,000 units/kg a day IV in 4 divided doses (maximum 24 million units).

Oral continuation: amoxicillin 1 g orally three times daily (or phenoxymethylpenicillin 1 g orally four times daily) for 6 to 12 months in total. Stop only when imaging shows resolution. Children: amoxicillin 30 mg/kg three times daily (maximum 1 g).

Penicillin allergy

• Doxycycline 100 mg orally twice daily.
• Ceftriaxone 2 g IV once daily (for those without anaphylaxis).
• Clindamycin 600 mg IV every 8 hours, then 450 mg orally every 8 hours.
• Renal dose adjustment is needed for high-dose penicillin (accumulation can cause seizures).

Surgery: percutaneous or open drainage of abscesses, excision of sinus tracts, and resection of the involved segment of bowel where there is obstruction or the mass cannot be distinguished from malignancy. Cefazolin 2 g IV before incision with metronidazole 500 mg IV.

Pelvic disease: remove the IUD, and give the same antibiotic course.

Monitoring: CRP and imaging at 4 to 6 weeks and every 3 months. Relapse occurs in under 10% when the course is complete.

Counsel on completing the long antibiotic course, dental review, and avoiding IUDs that remain over 5 years.