Abstract
Primary cutaneous actinomycosis of the extremity is extremely rare. It is usually misdiagnosed clinically as soft tissue tumour or soft tissue infection. We present the case of a 55-year-old woman with primary cutaneous actinomycosis of the right forearm that had been erroneously diagnosed as soft tissue tumour. It had probably occurred following direct inoculation of the micro-organism after a monkey bite. The patient was successfully treated with surgical excision followed by treatment with antibiotics.
Introduction
Actinomycosis is a chronic and granulomatous suppurative bacterial infection caused by endogenous anaerobic Gram positive bacteria. It is commonly seen in tropical countries. The usual sites of involvement are: cervicofacial; thoracic; abdominal; or pelvic. 1 Primary actinomycosis of the extremities is very rare and is mostly associated with external trauma and bites. Cutaneous involvement is well documented and is usually secondary to local extension, probably to haematogenous spread from various sites. 2 It is usually clinically misdiagnosed as soft tissue tumour or soft tissue infection. Therefore, the diagnosis requires a high index of clinical suspicion in patients with chronic non-healing wound in the extremities. We report a patient with primary cutaneous actinomycosis who presented with a subcutaneous nodule on her forearm.
Case history
A 55-year-old woman presented with a soft tissue swelling on her right forearm measuring approximately 8 × 7 cm that had been present for 5–6 years and which had been increasing in size for several months. The swelling was soft, nodular and non-tender. Her vitals were normal with no palpable lymphadenopathy. A clinical diagnosis of lipoma was made and she was given fine needle aspiration cytology (FNAC), which revealed a non-specific acute inflammatory lesion. An acid-fast bacilli staining was negative. It was recorded as inflammatory lesion/inflammatory change in a lesion. A repeat FNAC or excision biopsy was advised after the infection had been controlled. An excision biopsy revealed a soft, well-encapsulated nodular lesion with attached fibrofatty soft tissues. On cut section, there was a cystic cavity, the inner surface of which revealed grey-yellow to grey-brown granular material adherent to the wall (Figure 1a). Microscopic examination (Figure 1b) revealed fibroadipose and fibrocollagenous tissue densely infiltrated by acute and chronic inflammatory cells along with colonies of intertwined radiating filaments, capped by eosinophilic hyaline material, creating a sunburst appearance, consistent with the diagnosis of actinomycosis. This was confirmed by a Gram stain, periodic acid Schiff (PAS) stain and a Gomori methanamine silver stain. Staining for acid-fast bacilli was also performed in order to rule out nocardial infection. A detailed retrospective history revealed a past history of trauma caused by a monkey bite about 7–8 years earlier. There were two episodes of abscess formation with pus discharge that healed with antibiotic treatment given by a private practitioner. We were unable to confirm a typical history of sulphur granules.
(a) A photograph of a cystic lesion. (b) A photomicrograph showing actinomycotic colonies composed of a delicate filamentous centre (basophilic) and radially oriented peripheral (acidophilic) projections (haematoxylin and eosin stain 40×)
Discussion
Actinomycosis is a rare infectious bacterial disease primarily caused by Gram positive, non-sporing anaerobic bacillus such as Actinomyces israelii or Actinomyces gereneseriae. It occurs frequently in cattle as a disease called lumpy jaw but is rarely seen in humans. 3 In humans, it is primarily a commensal microbe found in normal oral cavities including tonsillar crypts, dental plaques, carious teeth and the female genital tract. However, the infection usually occurs after direct inoculation following traumatic injury, including punctured wounds, dental extractions, compound fractures or animal bites. 2 It has never been reported as being found outside the body and seems to have an exclusively endogenous habitat, particularly in the head, neck, thorax and abdomen. Cutaneous infection requires non-intact skin to invade and an anaerobic environment in order to cause the illness. 1 Primary cutaneous actinomycosis of an extremity is very rare with less than 50 cases reported in the published literature. Its clinical presentation is usually indolent and manifests as nodular lesions, subcutaneous abcess or even mass lesion mimicking a tumour. 4 Actinomycosis abscesses grow larger as the disease progresses and may even penetrate the surrounding bone and muscle to the skin, where they break open and leak a large amount of pus. The purulent leakages via the sinus cavities contain sulphur granules which contain progeny bacteria. 4
Conclusion
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. Although culture is definitive, it is difficult to cultivate actinomycetes from a clinical specimen. The histological picture is one of suppurative inflammation with abscess- and pus-filled sinus tracts in which bacteria form typical granular colonies (called sulphur granules) composed of radiating Gram positive filaments or club-shaped structure. 2 In our case, the patient presented with a nodular, cystic mass mimicking neoplastic soft tissue lesion, which has rarely been reported in the published literature.
Treatment of actinomycosis consists of surgical intervention and the appropriate antimicrobial therapy. Prognosis is generally excellent. Penicillin is the drug of choice and tetracycline is the alternative for penicillin-allergic patients. 5