Actinomycosis is a rare, slowly progressive bacterial infection caused by various species of the Actinomyces genus, most notably Actinomyces israelii. This condition is characterized by the formation of indurated, abscess-filled masses that often develop into chronic, pus-draining channels called sinus tracts. Actinomycosis is serious because it spreads locally through tissue planes, often leading to extensive tissue damage. The infection is difficult to diagnose in its early stages due to its subacute, non-specific presentation, which can mimic other diseases like cancer or tuberculosis.
Understanding the Cause of Actinomycosis
The bacteria responsible for actinomycosis are typically harmless residents, or commensals, within the human body. Actinomyces species colonize the mucous membranes of the mouth, throat, gastrointestinal tract, and the female genital tract. Since the bacteria are already present, the resulting infection is endogenous, meaning it arises from within the person’s own body.
Infection begins when the protective mucosal barrier is disrupted, allowing the bacteria to move into deeper, normally sterile tissues. Common causes of disruption include dental procedures, tooth decay, trauma, surgery, aspiration of oral secretions, or the presence of a foreign body like an intrauterine device (IUD). Actinomyces are anaerobic or microaerophilic, thriving in environments with low or no oxygen. Tissue damage reduces oxygen tension, creating the ideal low-oxygen conditions necessary for the bacteria to multiply and establish an infection.
Symptoms Based on Location in the Body
The clinical presentation of actinomycosis is highly varied, depending on the site of the initial barrier breach and subsequent spread. The infection is chronic and slow-growing, often taking weeks or months for noticeable symptoms to appear. The hallmark lesion across all forms is an indurated, “woody” mass that eventually forms multiple, interconnected abscesses and draining fistulas.
Cervicofacial Actinomycosis
The cervicofacial region, including the face, neck, and jaw, is the most frequent site of infection, accounting for 50–70% of cases. This form is often called “lumpy jaw” because it starts as a slowly growing, hard, non-tender lump under the skin or oral mucosa. The infection progresses to form sinus tracts, which are tunnels that open onto the skin and discharge a purulent fluid. This discharge often contains “sulfur granules,” which are yellowish, rounded clumps of tangled Actinomyces filaments and cellular debris.
Thoracic Actinomycosis
Thoracic actinomycosis, which affects the chest and lungs, usually results from the aspiration of oral secretions containing the bacteria. Symptoms are non-specific and mimic other serious pulmonary diseases like tuberculosis or lung cancer. Patients may experience a chronic cough, chest pain, fever, and weight loss. In advanced stages, the infection can spread directly to the pleura, ribs, and chest wall, potentially leading to chronic draining sinuses on the skin of the chest.
Abdominal Actinomycosis
Abdominal actinomycosis is difficult to diagnose because its symptoms are vague and non-specific, often involving the intestines, especially the cecum and appendix. This form often follows abdominal surgery, trauma, or a perforated viscus like a ruptured appendix. Common symptoms include low-grade fever, chronic abdominal pain, changes in bowel habits, and the sensation of an abdominal mass. The infection can form fistulas between the bowel and the skin, or between different organs.
Pelvic Actinomycosis
Pelvic actinomycosis is associated with the long-term use of intrauterine devices (IUDs), which can cause chronic trauma to the endometrium and provide a nidus for bacterial colonization. Symptoms can resemble pelvic inflammatory disease, including lower abdominal or pelvic discomfort, abnormal vaginal bleeding, and a foul-smelling vaginal discharge. The infection can form tubo-ovarian abscesses or pelvic masses that may resemble gynecologic malignancies, making accurate diagnosis a challenge.
Diagnosis and Long-Term Treatment
Diagnosing actinomycosis is challenging due to the infection’s slow progression and its capacity to mimic other diseases. Imaging studies, such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI), are used to determine the extent of the lesion and locate deep-seated abscesses or masses. Definitive confirmation requires the identification of the bacteria or the characteristic sulfur granules from infected tissue.
A tissue biopsy, aspiration of fluid from an abscess, or collection of discharge from a sinus tract are the preferred methods for obtaining a diagnostic sample. Culturing Actinomyces is difficult because the bacteria are fastidious anaerobes, grow slowly, and companion bacteria often overgrow them. The presence of sulfur granules, which are examined microscopically, provides strong presumptive evidence for the infection.
The treatment regimen requires high-dose, prolonged antibiotic therapy. Penicillin or amoxicillin is the standard treatment choice, often started intravenously for several weeks, followed by an oral regimen. This protracted treatment, typically lasting from 6 to 12 months, is necessary because the bacteria form dense, walled-off colonies that are difficult for the medication to penetrate. If large abscesses or necrotic tissue have formed, surgical intervention may be required to drain them, remove the diseased tissue, and allow the antibiotics to reach the infection site. For pelvic cases associated with an IUD, removal of the device is also necessary to eradicate the infection.