Actinomycosis

Actinomycosis is an uncommon subacute or chronic bacterial infection that causes both suppurative and granulomatous inflammation. Characteristics include localised swelling with suppuration, abscess formation, fibrosis and sinus drainage of pus containing "sulphur granules".

Actinomycetes are normal colonising organisms of the oral cavity and may also be present in the lower gastrointestinal and genito-urinary tracts. They should be considered facultatively pathogenic commensals, requiring a break in the mucous membranes or devitalised tissue to invade deeper body structures and cause illness.

Actinomycosis is almost invariably a synergistically-mixed infection of several species of actinomyces and other bacteria - some would consider the plural actinomycoses more correct because of this polyaetiology. Actinomyces israelii and A. gerencseriae are the most commonly encountered organisms in the human forms of the disease. Infections tend to develop in tissue adjacent to mucous membranes; oral and cervicofacial infections are most common but any body site can be infected and, rarely, disseminated spread can occur.

Actinomycosis is a great 'mimic', and symptoms and signs may initially be thought to be due to other diseases, particularly malignancy.¹ Failure to consider the diagnosis can lead to unnecessary surgery and delay in adequate treatment.

• Actinomyces infection is commonest between the ages of 25 and 50 with a male preponderance of 3:1.
• Infections have become rare in developed countries, probably due to improved dental hygiene and the use of antibiotics.
• Site of infection:
  • 50 to 70% of cases occur in the head and neck.
  • 15 to 20% are thoracic.
  • 10 to 20% are in the abdomen or pelvis.

Risk factors

• Poor oral hygiene with dental decay.
• Previous abdominal surgery.
• Areas of devitalised tissue, e.g. head or neck malignancies that have been treated with radiotherapy.³

HIV does not seem to increase risk significantly.⁴

Presentation will vary according to the site of infection.

Head and neck

History:

• Check for dental surgery, trauma to the mouth, foreign bodies (e.g. fishbones or bone splinters), poor oral hygiene with dental decay or periodontal disease.
• Chewing is difficult if there is involvement of the muscles of mastication.
• Fever is variable.

Examination may show some of the following:

• Nodular lesions at the angle of the jaw, slowly increasing in size and number to form sinuses that open on to the cheek or under the mandible.
• Nodules are not tender except possibly in the early stages. Later they become hard.
• Multiple sinuses may occur with exacerbations and remissions.
• There is livid discolouration of the skin over the lesion.
• Lymph nodes are not palpable.
• Trismus is present if the muscles of mastication are involved.

Thorax

Thoracic lesions are much less common than the cervicofacial form of the disease. They tend to occur following aspiration or inhalation of material from the mouth or a contaminated foreign body.
History may reveal:

• Fever
• Dry or productive cough
• Shortness of breath, chest pain or haemoptysis
• Weight loss, fatigue, anorexia

Examination may show:

• Cachexia
• Abnormal breath sounds
• Sinus tracts draining from the chest wall

Abdomen

History generally includes previous abdominal surgery. Symptoms are non-specific and include:

• Low-grade fever
• Weight loss
• Fatigue
• Change in bowel habit
• Vague abdominal discomfort
• Nausea and vomiting
• Sensation of a mass

Examination may show:

• Cachexia
• A mass (most often in the right lower quadrant but sometimes in the left lower quadrant) - firm to hard, non-tender and often fixed to the underlying tissue
• Sinus tracts with drainage from either the abdominal wall or the perianal region

Pelvis

• Usually an IUCD has been fitted, particularly old plastic devices, and present over many years. Infection with a first generation IUCD was common but it is much rarer with copper containing devices or IUS. The fact that copper devices and the IUS have to be changed every 5 years may be important.
• Symptoms include lower abdominal discomfort, abnormal vaginal bleeding or discharge.
• Examination tends to reveal an adnexal mass.

This depends upon the site but includes:

• Malignancy
• Tuberculosis
• Appendicitis⁵
• Other causes of abdominal masses
• Crohn's disease
• Diverticular disease
• Pelvic inflammatory disease (PID)

Blood tests

• FBC may show anaemia and mild leukocytosis.
• Inflammatory markers (e.g. ESR) are often elevated.
• Blood chemistry is normal unless there is hepatic involvement, in which case alkaline phosphatase will be raised.

Microbiology

• Pus, sinus discharge, deep needle aspiration or biopsies provide suitable specimens. Swabs, sputum and urine specimens are not helpful.
• Rapid transportation to the laboratory, ideally in an anaerobic transport medium, gives the best results.
• Gram staining reveals the typical beaded, branched, Gram-positive filamentous rods.
• Culture requires incubation under anaerobic conditions for at least 48 hours, but the isolation and confident identification of actinomycetes may take considerably longer.
• Nucleic acid probes and polymerase chain reaction (PCR) methods are becoming available for more rapid identification.
• The preliminary diagnosis of actinomycosis also can be made by examining sulphur granules microscopically (crush between 2 slides with 1% methylene-blue solution stain). Sulphur granules (up to 1 mm diameter) macroscopically are yellow/red/brown particles with a cauliflower appearance at low magnification. Note: whilst these granules are characteristic, they are not pathognomonic.

Imaging

• CXR may show a poorly-defined mass, pneumonitis or cavitation +/- pleural involvement. Hilar lymph nodes are uncommon. A mass may extend across fissures or pleura, invade the adjacent chest wall or cause destruction of ribs. Radiologically, actinomycosis may be difficult to differentiate from TB or bronchial carcinoma.
• CT scans of any site usually reveal an infiltrating mass with focal areas of decreased attenuation that enhance with contrast. The mass tends to invade surrounding tissues.

Histology

• CT or ultrasound-guided fine needle aspiration (FNA) or biopsy can be used to obtain clinical material for diagnosis.
• Actinomycosis is characterised by a mixture of suppurative and granulomatous inflammation, connective tissue proliferation and the presence of sulphur granules.

Drugs

• Penicillin is the drug of choice. Resistance is rare. High doses have to be given for prolonged courses.
• In those who are allergic to penicillin, options include tetracyclines, erythromycin, doxycycline and clindamycin. However, response to tetracyclines and ciprofloxacin is poor and a beta lactam antibiotic, perhaps with beta lactamase inhibitors, should be the first choice.⁶
• Parenteral therapy may be required for severe infection, usually for 1-2 weeks, before switching to the oral route for up to a year's course. The exact duration and route of treatment will depend upon the response of the individual.⁷

Surgical

Surgery may be required for incision and drainage of abscesses, excision of sinus tracts and fibrosis, decompression and relief of obstruction.

• Osteomyelitis of the mandible, ribs, and vertebrae
• Brain abscess, chronic meningitis, cranial and spinal infections of the dural spaces
• Endocarditis
• Disseminated actinomycosis
• Hepatic abscess¹¹

Actinomycosis is increasingly being recognised as a major factor and poor prognostic indicator in infected osteoradionecrosis and bisphosphonate-associated osteonecrosis of the jaws.¹²

• If diagnosed early and treated adequately, cervicofacial and cutaneous actinomycosis have a good prognosis.
• Thoracic, abdominal and systemic manifestations of the disease remain serious conditions requiring aggressive antibiotic treatment and surgery.
• The outcome can on occasion still be fatal.

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• NHS Choices; Actinomycosis