Actinomycosis is a slowly progressive, suppurative infection characterized by fistula formation. A number of gram-positive, non–spore-forming bacteria from the genus Actinomyces are the etiologic agents. It is encountered worldwide in 3 main clinical forms: cervicofacial, thoracic, and abdominal. Metastatic lesions to other sites are also reported. With appropriate therapy, most patients with cervicofacial or abdominal infection recover completely.
EPIDEMIOLOGY AND PATHOGENESIS
Actinomyces species are part of the normal flora of the human gastrointestinal tract. Actinomycosis is not considered a communicable disease. It affects both immunocompetent and immunocompromised individuals. Diabetes mellitus, malnutrition, and immunosuppression may be predisposing factors. Although uncommon in children, actinomycosis has been reported even in infancy. The disease is not related to occupation, season, or race.
With the use of 16S rRNA sequencing, at least 21 species of Actinomyces have been identified in humans. A israelii, the species that most commonly produces human disease, is part of normal oral flora. A viscosus, A naeslundii, A odontolyticus, A meyeri, and Propionibacterium (Arachnia) propionica are also established etiologic agents. Actinomyces species require an anaerobic or microaerophilic environment for growth and demonstrate gram-positive branching filaments, often appearing as beaded filaments. It has also been shown that Actinomyces species require the presence of other bacteria to multiply. Thus, actinomycosis is frequently polymicrobial in nature, and concomitant bacterial species such as Eikenella corrodens, Aggregatibacter actinomycetemcomitans, Fusobacterium, Capnocytophaga, Staphylococcus, microaerophilic streptococci, and Enterobacteriaceae are often isolated from actinomycotic lesions.
Actinomycosis may present as a chronic indolent process, as an acute rapidly progressive infection, or somewhere between these extremes. However, the most common presentation remains the chronic indolent form. The hallmark of actinomycosis is the spread of infection that fails to respect fascial or tissue planes.
Cervicofacial disease is the most common type of infection in immunocompetent individuals, accounting for 60% of patients with actinomycosis. Predisposing factors include gingivitis, gingival trauma, dental procedures, and tooth-related infections. It presents as a slowly progressive, indurated swelling or mass, usually at the angle of the jaw (lumpy jaw), but it can occur anywhere on the cheek, mandible, or anterior neck. The duration of illness is typically several months. Pain is seldom prominent. A low-grade fever may occur in as many as 50% of patients. Most patients do not appear systemically ill. Inflammatory markers such as the erythrocyte sedimentation rate and C-reactive protein as well as the white blood cell count are often normal.
The clinical progression may be marked by episodes of suppuration that are contained by reactive fibrosis. Although the lesions may be intermittently fluctuant and appear as cold abscesses, they will eventually progress to a hard mass with a lumpy appearance. The disease spreads to adjacent tissues without regard to anatomic structures. Lymphatic spread and associated lymphadenopathy ...