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Contributors: Paritosh Prasad MD, Edith Lederman MD, Noah Craft MD, PhD
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Actinomycosis is a group of diseases broken down into two groups: endogenous and exogenous. In general, actinomycosis usually refers to the endogenous form, while the exogenous form involving the lower extremities is usually referred to as a mycetoma. Endogenous actinomycosis is caused by anaerobic bacteria from the actinomycetales group, usually Actinomyces israelii.

The Actinomyces bacteria responsible for the endogenous form have a worldwide distribution and are found in normal oral, intestinal, and urogenital flora. Under conditions of poor dental hygiene or poor health, the bacteria become more pathogenic. Infection begins following a breach of mucous membranes and leads to formation of granulomatous tissue, fibrosis, abscesses, sinus tracts, and fistulas. Clinical presentations are subacute to chronic and include cervicofacial, thoracic, abdominal, and pelvic. These are direct extensions and sinus tracts from the oral cavity, the lungs, the gastrointestinal tract, and the genitourinary tract, respectively.
  • Cervicofacial actinomycosis is the most common clinical form and typically arises following odontogenic infection or dental surgery. Infection can result from poor oral hygiene in patients with predisposing factors such as dental caries, gingivitis, oral trauma, and other oral infections.
  • Thoracic actinomycosis typically results from aspiration of secretions in patients with poor oral hygiene, alcohol use disorder, chronic lung disease, or preexisting dental disease.
  • Abdominal actinomycosis most commonly affects the appendix, cecum, or colon following a mucosal breach from recent abdominal surgeries or colonic perforation.
  • Pelvic actinomycosis typically arises in women with history of intrauterine device (IUD) use.
Primary cutaneous actinomycosis is rare and has a variable presentation. It is usually, although not always, associated with a history of external trauma.


A42.89 – Other forms of actinomycosis

11817007 – Actinomycosis

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Differential Diagnosis & Pitfalls

Endogenous actinomycosis:
For the differential diagnosis of exogenous actinomycosis, see mycetoma.

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Last Reviewed: 11/08/2017
Last Updated: 12/01/2017
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Actinomycosis (Cervicofacial) : Draining sinus, Poor oral hygiene, Soft tissue swelling
Clinical image of Actinomycosis
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