Actinomycosis is a chronic (slowly progressive) infection caused by various bacterial species of the Actinomyces genus, most commonly Actinomyces israelii. Actinomyces are normal inhabitants of the mouth, gastrointestinal tract, and female genital tract, and do not cause an infection unless there is a break in the skin or mucosa. Actinomyces also appear to require the presence of other accompanying bacteria in order to cause disease.
The disease is characterised by the formation of abscesses and draining sinus tracts (small tunnels which open onto the surface of the skin or mucous membranes and drain pus). The draining pus contains yellow granules called sulphur granules (named from the colour of the granules, not the content).
Historically, actinomycosis was thought to be a fungal disease because of the appearance of the bacteria and the slowly progressive nature of the illness.
Actinomycosis is relatively rare, but the following factors increase the risk of infection:
- Poor oral hygiene followed by dental surgery or trauma
- Impaired immunity e.g. immunosuppressive medications or chronic conditions such as diabetes mellitus
- Inhabitants of tropical countries
Actinomycosis is to be differentiated from actinomycetoma, which is a chronic infection of the skin and subcutaneous tissue, usually involving the foot (see mycetoma). Actinomycetoma is caused by different species of Actinomyces that are found in soil and plant material in tropical regions.
Cervicofacial (neck and head) actinomycosis is the most common form of infection, accounting for 50-70% of cases. Dental surgery, oral or facial trauma, or local tissue damage caused by cancer or radiation therapy commonly precede infection. The infection usually begins with a slowly progressive, non-painful, hard lump in the cheek or around the jaw. This evolves into abscesses and draining sinus tracts. Surrounding tissues become swollen. Fever and other symptoms of systemic infection are sometimes present. Actinomycosis around the jaw can cause trismus (prolonged spasm of the jaw muscles).
Lymph nodes are not usually enlarged and there is generally little pain, unless adjacent structures are compressed. The infection slowly spreads to surrounding tissues and organs such as the scalp, eyes, ears, tongue, larynx, and trachea. Invasion of adjacent bone occasionally occurs. Infection may spread to the meninges (the membranes surrounding the brain and spinal cord) causing meningitis.
Abdominal disease (10-20% of cases) usually follows a break in the gastrointestinal mucosa, e.g. following surgery, appendicitis, diverticulitis, or ingestion of foreign bodies such as chicken or fish bones. This disease is difficult to diagnose as patients often have non-specific slowly progressive symptoms such as fever, weight loss, diarrhoea or constipation, and abdominal pain. Any abdominal organ can become involved by direct spread of the disease. Sinus tracts are occasionally found extending to the skin of the abdominal wall or to the mucosal tissue of the rectum or anus.
Pulmonary disease (15-20% of cases) is usually caused by aspiration (inhalation) of oral or gastrointestinal secretions. The infection presents with slowly progressive non-specific symptoms such as cough, sputum production, breathing difficulties, and chest pain. The infection can slowly spread to involve local structures such as the heart and the chest wall, with sinus tracts occasionally extending to the skin of the chest.
Pelvic actinomycosis is rare and is associated with the use of intrauterine contraceptive devices. Common symptoms of this infection include lower abdominal discomfort, abnormal vaginal bleeding, and vaginal discharge.
Primary cutaneous actinomycosis
Primary cutaneous actinomycosis is very uncommon and affects exposed skin after direct implantation of the organism during an injury.Ï
- Material obtained from aspirating an abscess or sinus tract, or from a biopsy specimen can be cultured in the laboratory; strict growth conditions are required. Often a variety of accompanying bacteria will be present.
- Sulphur granules may be examined under a microscope for features characteristic of Actinomyces; however this is not a conclusive test, as another bacterium called Nocardia has a similar appearance.
Actinomycosis is treated with antibiotics, such as penicillin. Alternative antibiotics include tetracyclines, erythromycin, and clindamycin. Prolonged treatment is often required to prevent relapse. In some cases, surgery may also be necessary to drain deep abscesses and to remove the sinuses.