actinomycosis

Actinomycosis is a chronic granulomatous infection caused by Actinomyces species, principally Actinomyces israelii, which are anaerobic, Gram-positive, branching filamentous bacteria that are part of the normal mucosal flora of the oral, gastrointestinal, and female genital tracts. Disease occurs when mucosal barriers are breached, allowing local infection and spread into adjacent tissues, often forming sinus tracts and discharging sulfur granules.

Clinically, actinomycosis presents with indolent swellings, mass-like lesions, and draining sinus tracts. The cervicofacial region is the most commonly affected area, often after dental disease or trauma; thoracic, abdominal and pelvic, and central nervous system forms occur less frequently and may mimic malignancy or other infections.

Diagnosis is challenging; culture requires strict anaerobic conditions and prolonged incubation and can be negative. Histopathology showing sulfur granules—dense colonies of filamentous bacteria within inflammatory debris—and the Splendore-Hoeppli phenomenon supports the diagnosis. Imaging can reveal invasive, mass-like lesions; microbiology should distinguish Actinomyces from nocardia, which is partially acid-fast.

Treatment involves prolonged antibiotic therapy. The standard regimen is high-dose intravenous penicillin G for 2–6 weeks, followed by long-term oral antibiotics (penicillin V or amoxicillin) for 6–12 months. Alternatives for penicillin allergy include doxycycline, tetracycline, erythromycin, or clindamycin. Surgical drainage, debridement, or resection may be necessary for extensive disease or to manage abscesses and fistulas.

Prognosis is generally favorable with appropriate therapy, though relapse can occur if treatment is shortened. Early recognition and management of underlying dental or mucosal breaches help reduce risk.