33-33: Actinomycosis

Actinomyces israelii and other species of Actinomyces occur in the normal flora of the mouth and tonsillar crypts. They are anaerobic, gram-positive, branching filamentous bacteria (1 mcm in diameter) that may fragment into bacillary forms. When introduced into traumatized tissue and associated with other anaerobic bacteria, these actinomycetes become pathogens.

The most common site of infection is the cervicofacial area (about 60% of cases). Infection typically follows extraction of a tooth or other trauma. Lesions may develop in the gastrointestinal tract or lungs following ingestion or aspiration of the organism from its endogenous source in the mouth. Interestingly, T whipplei, the causative agent of Whipple disease, is an actinomycete and therefore is related to the species that cause actinomycosis.

A. Symptoms and Signs

1. Cervicofacial actinomycosis

Cervicofacial actinomycosis develops slowly. The area becomes markedly indurated, and the overlying skin becomes reddish or cyanotic. Abscesses eventually draining to the surface persist for long periods. “Sulfur granules”—masses of filamentous organisms—may be found in the pus. There is usually little pain unless there is secondary infection. Trismus indicates that the muscles of mastication are involved. Radiography may reveal bony involvement. Cervicofacial or thoracic disease may occasionally involve the CNS, most commonly brain abscess or meningitis.

2. Thoracic actinomycosis

Thoracic involvement begins with fever, cough, and sputum production with night sweats and weight loss. Pleuritic pain may be present. Multiple sinuses may extend through the chest wall, to the heart, or into the abdominal cavity. Ribs may be involved. Radiography shows areas of consolidation and in many cases pleural effusion.

3. Abdominal actinomycosis

Abdominal actinomycosis usually causes pain in the ileocecal region, spiking fever and chills, vomiting, and weight loss; it may be confused with Crohn disease. Irregular abdominal masses may be palpated. Pelvic inflammatory disease caused by actinomycetes has been associated with prolonged use of an intrauterine contraceptive device. Sinuses draining to the exterior may develop. CT scanning reveals an inflammatory mass extended to involve bone.

B. Laboratory Findings

The anaerobic, gram-positive organism may be demonstrated as a granule or as scattered branching gram-positive filaments in the pus. Anaerobic culture is necessary to distinguish actinomycetes from nocardiae because specific therapy differs for the two infections. Histopathology examination of affected tissue and bone is useful in identifying organisms that are fastidious and slow to culture.

Penicillin G is the drug of choice. Ten to 20 million units are given via a parenteral route for 4–6 weeks, followed by oral penicillin V, 500 mg four times daily. Alternatives include ampicillin, 12 g/day intravenously for 4–6 weeks, followed by oral amoxicillin, 500 mg three times daily, or doxycycline, 100 mg twice daily intravenously or orally. Response to therapy is slow. Therapy should be continued for weeks to months after clinical manifestations have disappeared in order to ensure cure. Surgical procedures such as drainage and resection may be beneficial. With penicillin and surgery, the prognosis is good. The difficulties of diagnosis, however, may permit extensive destruction of tissue before the diagnosis is identified and therapy is started.