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Actinomycosis: A rare soft tissue infection

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Actinomycosis: A rare soft tissue infection
Mohammad S Fazeli MD, Hamed Bateni MD
Dermatology Online Journal 11 (3): 18

From The Department of Surgery , Imam Khomeini Hospital, Tehran.


Actinomycosis is a chronic and suppurative infection caused by an endogenous Gram-positive bacterium. The usual sites of infection are the head and neck, thorax, and abdomen. Primary cutaneous actinomycosis is very rare and usually associated with external trauma and local ischemia. We report on the case of a primary cutaneous actinomycosis of the thigh in a 34-year-old man. The patient was treated successfully with surgical resection and combined antibiotic therapy, and eventually cutaneous reconstructive surgical procedure.


Actinomycosis is an anaerobic, Gram-positive bacterial infection, seen in different regions of the body. Actinomycosis is caused in man by Actinomyces israelii and in animals by Actinomyces bovis. Also, human infections due to A. bovis, A. naeslandii, and A. viscosus have been documented. The infection is commonly seen in tropical countries and is characterized by chronic and progressive suppurative inflammation, typically presenting on the neck, thorax, and abdomen. Primary cutaneous actinomycosis is a rare entity, and the diagnosis requires a high index of clinical suspicion. Primary disease of the extremities is uncommon and sometimes has an association with trauma and bites.

Clinical synopsis

A 34-year-old, otherwise healthy normal man presented to the surgery ward 3 of Imam Khomeini hospital following a 2-week hospitalization in a dermatology ward for proximal left lower extremity skin lesion. The gross appearance of this 38 by 32 cm lesion consisted of local dusky red swellings, firm fluctuating nodules, and penetrating sinus tracts exuding a minimal purulent discharge. In these exudates, there were whitish and yellowish, or gray granules measuring 1-4 mm in diameter. The aggregate was surrounded by marked induration (Fig. 1). The lesion first appeared about 17 years ago, and grew gradually, experiencing some episodes of hemorrhage. Several hospital admissions and therapies including antibiotics did not have any effect on the disease. MRI imaging revealed involvement of gluteus maximus superiorly, skin and subcutaneous fat posterolateraly down to the midportion of the thigh, and extending between anterior and posterior muscular compartments anteroinferiorly, along with anterior displacement of gluteus medius. No obvious involvement of neurovascular bundles was noted. DSA ruled out underlying angiomatosis. All other test results including blood biochemistry, hematology, hemoglobin electrophoresis, STD serology, urine analysis and microbiology, and stool exam were within normal limits. Direct examination of the lesion and its granules showed the presence of lobulated bodies consisting of delicate branching and intertwining filaments similar to Actinomycotic mycetoma and the growth of Actinomyces sp. in the performed culture.

Figure 1
Figure 1: Gross appearance of the left thigh lesion.

The patient underwent surgery once the necessary tests were run. The lesion was excised as a whole during one operation. The specimen was 7-cm thick and the narrowest margin was 0.4 cm. the involved muscles were sacrificed. (Figs. 2-4). Thereafter he underwent a combination of IV penicillin G (5,000,000 U q.i.d.) and oral Cotrimoxazol (960 mg b.i.d.) for a month with marked improvement and received meshed split thickness skin graft acquired from the opposite thigh. He was discharged to continue the oral antibiotic for a year.

Figure 2 Figure 3
Figure 2. The external face of the excised lesion.
Figure 3. The inner face of the lesion.

Figure 4
Figure 4. The cross section of the specimen.

Pathologic findings

Two separate debridement and biopsy specimens were obtained over a 2-week period. The debrided tissue was obtained from the surface of the lesion and consisted of fragments of necrotic skin and fibroadipose tissue. The histological finding in the biopsy specimen was that of an infective granuloma forming a deep nodular process, with granulation tissue, epithelioid cells, plasma and giant cells, and degenerative changes. Large and deep abscesses and sinuses were found, which contained polymorphonuclear leukocytes and miscellaneous debris, along with the ray fungus and its filaments.

Figure 5 Figure 6
Figure 5. A deeply basophilic actinomycin(sulfur) granule is seen in subcutaneous tissue. Hematoxylin-Eosin stain, × 40
Figure 6. The photomicrograph shows a high power of the actinomycotic granule composed of a delicate filamentous center (basophilic) and radially oriented peripheral (acidophilic) projections. Hematoxylin-Eosin stain, × 400


Actinomycosis is believed to be acquired by endogenous implantation into deep tissues where anaerobic conditions prevail. Puncture wounds, dental extractions, or compound fractures are some of the routes of infection. A. israelii has been recovered from the normal mouth, from tonsils, and from carious teeth and is thought to be commonly present. The belief that infection is from endogenous sources is further confirmed by the fact that A. israelii has never been demonstrated in soil, in plants, or in any other object outside the body. Probably all cases of actinomycosis are closely connected with other contaminating bacterial infections.

Cutaneous localizations of actinomycosis generally occur by contiguity of underlying foci by direct inoculation or by spread through the bloodstream during a septicemic phase of the infection. In the latter case, there are often multiple lesions. Post-traumatic actinomycosis and cases associated with insect bites have also been described. Primary infections of the rectum and rarely of the perianal area, perianal and buttock area, and abdominal wall have been reported.

Cutaneous actinomycosis manifesting with nodular lesions that tend to form fistulae needs to be differentiated clinically from other chronic inflammatory skin diseases, such as cutaneous tuberculosis, sporotrichosis, and nocardiosis. Diagnosis is based on identification of sulphur granules (usually 1-6 mm in diameter) in pus and histological preparations, and preferably also by a positive culture. The histological picture is one of suppurative inflammation with abscesses and pus filled sinus tracts in which bacteria form typical granular colonies composed of radiating Gram-positive filaments.

Acknowledgement: Very few articles are the result of one person's efforts. It gives us great pleasure to thank the staff of surgical ward 3 and OR 2 of Imam Khomeini hospital for their cooperation. Thanks are due to them, to Drs Jafarian MD, Azmudeh Ardalan MD, and S.Rezaee Khiabanlou MD for their substantial contribution.


1: Ermis I, Topalan M, Aydin A, Erer M. Actinomycosis of the frontal and parotid regions. Ann Plast Surg 2001; 1:55-58.

2: Wee SH, Chang SN, Shim JY, Chun SL, Park WH. A case of primary cutaneous actinomycosis. J Dermatol. 2000 Oct;27(10):651-4.

3: Reiner SL, Harrelson JM, Miller SE, Hill GB, Gallis HA. Primary actinomycosis of an extremity: a case report and review. Rev Infect Dis. 1987;9(3):581-9.

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