OVERVIEW: What every practitioner needs to know

Actinomycosis refers to the disease entity caused by any one of the organisms of the genus
Actinomyces. These organisms are filamentous gram-positive, facultative anaerobic rods that are frequent commensals of the human gastrointestinal, respiratory, and female genitourinary tract.

Are you sure your patient has actinomycosis? What are the typical findings for this disease?

The classic presentation of actinomycosis typically is the indolent development of a firm mass, which often develops fistulous tracts that drain purulent material or sulfur granules. The masses often take on an extremely firm or “woody” texture such that they are often confused with malignancy. There is, however, a subset of patients who present more acutely, with rapid development of induration, erythema, and suppuration. Clinically, actinomycosis typically takes one of three forms: cervicofacial, thoracic, or abdominopelvic.

Cervicofacial Actinomycosis

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Cervicofacial actinomycosis is overwhelmingly the most common form in pediatrics. It accounts for up to 49.1% of cases in some series, with as many as 75% of patients having symptoms for 6 months or longer. It frequently presents with the indolent development of a painless firm neck or mandibular mass. Sinus tracts may be present.

Thoracic Actinomycosis

Thoracic disease accounts for 15% of all cases of actinomycosis. Common symptoms include a chest wall mass (49%), chronic cough (40%), pain (36%), fever (35%), weight loss (35%), and chest wall–draining sinuses (15%). Hemoptysis is described in 55% of adults but is uncommon in children (9%).

Abdominopelvic Actinomycosis

Abdominopelvic actinomycosis involves the development of intraabdominal abscesses secondary to these organisms. The abscess most commonly develops in the ileocecal region (right lower quadrant)and presents as a hard, irregular right lower quadrant mass on examination. It may suppurate with fistulae to skin.

It often develops as a complication of appendicitis and may present with chronic/recurrent abdominal pain, fever, and weight loss, and imaging studies may be consistent with appendicitis.

Abdominopelvic actinomycosis is a potential cause of tuboovarian abscess.

Dissection into bladder and bowel can occur.

What other disease/condition shares some of these symptoms?

Cervicofacial actinomycosis:

Malignancy (in particular lymphoma), extrapulmonary tuberculosis, bacterial adenitis,
Bartonella, and jaw osteomyelitis

Thoracic actinomycosis

Mimics malignancy, pulmonary tuberculosis, and rib osteomyelitis

Abdominopelvic actinomycosis

Sarcoma, pelvic inflammatory disease, tuboovarian abscess, other polymicrobial abscess, appendicitis

What caused this disease to develop at this time?

Disruption of the normal mucosal barriers is often an inciting event for infection with this organism. One of the hallmarks of actinomycosis is its potential to dissect through tissue planes, disregarding normal anatomic barriers.

Cervicofacial actinomycosis: The most common predisposing factor for cervicofacial actinomycosis is some kind of disruption of the gingiva (35% in some series), typically as a consequence of dental caries (33%), extractions (12%), or trauma.

Thoracic actinomycosis: This type of actinomycosis is much more common in adults and is frequently associated with aspiration of oral secretions or foreign bodies, which then disrupt the normal bronchial mucosal barriers.

Abdominopelvic actinomycosis: This type of actinomycosis most often develops as a result of surgical complications or abdominal trauma. There may be a history, even remotely, of abdominal surgery or trauma. Intrauterine contraceptive devices have been associated with the development of pelvic actinomycosis and may be associated with menorrhagia, indolent pelvic/abdominal pain, vaginal discharge, and fever.

Other risk factors: A. naeslundii has recently been identified as an emerging pathogen in patients with chronic granulomatous disease.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

The diagnosis of actinomycosis is based primarily on culture results and histopathologic evaluation of tissue specimens. Histologic analysis may reveal filamentous clusters of organisms in a mat-like configuration; grossly macroscopic sulfur granules may be seen as well.

Diagnositic Pitfalls

It is worth noting that sulfur granules are not pathognomonic for actinomycosis and can be seen with other organisms, in particular Nocardia; an important distinction is that Nocardia organisms are acid-fast and actinomycetes are not.

Culture alone failed to yield an organism in as many as 50% of cases in older series. Tissue diagnosis is often necessary.

Actinomycetes often grow better in anaerobic culture than in aerobic culture.

Given that malignancy is high on the differential diagnosis of this entity, it would be reasonable to obtain tumor lysis studies, complete blood counts, and peripheral blood smears as well to establish an accurate diagnosis.

Would imaging studies be helpful? If so, which ones?

Imaging is useful to evaluate the extent of disease and possibly the response to therapy.

Computed tomography with contrast or magnetic resonance imaging with enhancement are ideal studies.

Chest radiography in thoracic disease classically reveals upper and lower lobe consolidation, pleural effusion, and rib periostitis.

If you are able to confirm that the patient has actinomycosis, what treatment should be initiated?

The cornerstone of treatment of actinomycosis includes extensive surgical debridement combined with administration of long-term antimicrobial agents.

Actinomyces is universally exquisitely sensitive to penicillin; penicillin and other β-lactams are considered the antibiotics of choice. Cephalosporins and clindamycin are useful alternatives for patients who are allergic to penicillin. It is worth noting that some species of actinomycetes have decreased susceptibility to piperacillin-tazobactam; there are also high rates of resistance to ciprofloxacin and metronidazole.

Most experts recommend prolonged courses of antibiotics (6-12 months). Many recommend 4-6 weeks of intravenous antibiotics before switching to oral agents to complete the course of therapy. Most experts would continue antimicrobial therapy for some time after obtaining clinical response. There are reports, however, of success with regimens as short as 10 days. There are very few well-designed studies regarding the duration of therapy.

It is also important to address any copathogens that are also isolated (such as
Staphylococcus aureus) with antimicrobial therapy.

What are the adverse effects associated with each treatment option?

Given the long duration of treatment, adverse drug events are not uncommon. Drug-induced neutropenia and thrombocytopenia are not uncommon with β-lactams. Other adverse events include renal insufficiency, drug allergy, drug rash, and central-line infection if the patient is being treated with IV therapy.

What are the possible outcomes of actinomycosis?

Most patients do well with treatment, and cure can be achieved in most patients. Rarely, there have been descriptions of intracranial extension of actinomycosis of the head and neck. Fistulous tracts are fairly common with all forms of the disease but typically resolve with treatment. Recurrence of disease with short courses of therapy are well described.

What causes this disease and how frequent is it?

Actinomycetes organisms are normal commensals of the human oropharynx, gastrointestinal and respiratory tracts, and the female reproductive tract. Actinomycetes israelii is the most common species of actinomycete to cause disease in humans, although disease can be caused by any number of species (e.g., A. odontolyticus,
A. viscosus, A. naeslundii).

It is worth noting that Propionibacterium acnes has rarely been described as a cause of disease clinically similar to actinomycosis. These infections are most often polymicrobial.

Studies in Germany have shown that in only 4.5% of cases is the actinomycete isolated alone. Among the most commonly isolated copathogens are Staphylococcus aureus (as high as 36.8% of cases), α-hemolytic streptococci, coagulase-negative staphylococci,
Fusobacterium, and Aggregatibacter (formerly
Actinobacillus) actinomycetemcomitans (up to 30% of cases).

Actinomycosis is an uncommon diagnosis in children.

How do these pathogens/genes/exposures cause the disease?

Actinomycetes cause disease typically after the normal mucosal barriers are breached. Once these are breached, the organisms have the potential to invade locally and cross fascial planes.

How can actinomycosis be prevented?

Given the strong association of cervicofacial disease with dental caries, good oral hygiene is an excellent preventive measure. The incidence of actinomycosis decreased substantially in the 20th century, believed in large part due to the availability of antibiotics and improved oral hygiene and nutrition.

What is the evidence?

The overwhelming majority of literature on this subject comes from studies in adults.

Feder, HM. “Actinomycosis manifesting as an acute painless lump of the jaw”. Pediatrics. vol. 85. 1990. pp. 858-64. (This article describes three pediatric cases of cervicofacial actinomycosis and reviews relevant literature.)

Bartlett, AH, Rivera, AL, Krishnamurthy, R. “Thoracic actinomycosis in children: case report and review of the literature”. Pediatr Infect Dis J. vol. 27. 2008. pp. 165-9. (This is a comprehensive review of the literature regarding thoracic actinomycosis in children.)

Yigiter, M, Kiyici, H, Arda, IS. “Actinomycosis: a differential diagnosis for appendicitis. A case report and review of the literature.”. J Pediatr Surg. vol. 42. 2007. pp. E23-6. (This article provides a useful description of this very rare presentation of actinomycosis in children.)