Asian Cardiovasc Thorac Ann 2004;12:165-167
© 2004 Asia Publishing EXchange Ltd
Actinomycosis: An Often Forgotten Diagnosis
Randolph HL Wong, MRCS,
Alan DL Sihoe, MRCS,
KH Thung, FRCS,
Innes YP Wan, FRCS,
Margaret BY Ip, MRCPath1,
Anthony PC Yim, FRCS
Department of Surgery
1 Department of Microbiology, Prince of Wales Hospital, Hong Kong, People’s Republic of China
For reprint information contact: Anthony PC Yim, FACS Tel: 852 2632 2629 Fax: 852 2647 8273 Email: yimap{at}cuhk.edu.hk Division of Cardiothoracic Surgery, Department of Surgery, The Chinese University of Hong Kong, Shatin, Hong Kong, People’s Republic of China.
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ABSTRACT
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We report a case of actinomycosis presenting as a chest wall mass in a 35 year-old man. Thoracic actinomycosis poses a diagnostic challenge to clinicians not only because it is uncommon and often forgotten, but also because culture of the causative microbes is technically difficult. The classic microscopic appearance of this Gram-positive bacteria associated with surrounding sulfur granules often forms the basis of diagnosis.
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INTRODUCTION
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It is estimated that 15%–25% of cases of actinomycosis present primarily in the thorax, and thoracic actinomycosis is an uncommon cause of pleural effusion.1,2 We describe a case of pleuropulmonary actinomycosis presenting as a chest wall abscess.
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CASE REPORT
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A 35 year-old man presented with a febrile chest infection of two weeks’ duration, and a loculated right pleural effusion demonstrated on chest radiography and computed tomography of the thorax. He was a chronic smoker but had an otherwise unremarkable medical history. Sputum sampling, pleural aspiration, and percutaneous pleural biopsy failed to yield a positive microbiological or cytological diagnosis. An exploration by video-assisted thoracic surgery (VATS) was performed for the indeterminate effusion. Intraoperatively, there was diffuse pleural symphysis compatible with post-pneumonic fibrosis, but no discrete pulmonary or pleural lesions for biopsy. The chest infection resolved on intravenous cefuroxime given empirically.
Three months later, he was found to have a tender mass of 3 cm in diameter over the right lower chest wall. The site of the lesion did not correspond to any of the VATS ports. Thoracic computed tomography revealed a small residual right pleural effusion and a localized soft tissue swelling over the right lower ribs without obvious bony destruction. Percutaneous fine-needle aspiration (FNA) and a Tru-Cut biopsy of the mass were performed with histopathological studies, which showed chronic inflammatory changes only. An incisional biopsy of the mass was carried out, yielding a semisolid white material. Histology revealed gram-positive filamentous bacteria associated with characteristic sulfur granules (Figure 1
), and hence a diagnosis of actinomycosis was made. Microbiological culture of the tissue yielded Propionibacterium propionica on prolonged incubation. The patient was treated with a 1-month course of intravenous benzylpenicillin followed by 5 months of oral amoxicillin. His chest wall mass regressed in size in response to treatment, and he made an excellent recovery.
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Figure 1. Histology slide showing Gram-positive filamentous bacteria (black arrow) on a background of sulfur granules (white arrow). Gram stain, original magnification x 400.
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DISCUSSION
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Actinomycosis is the collective term for the chronic suppurative noncontagious infection caused by a variety of Gram-positive, non-spore-forming, non-acid-fast anaerobic or microaerophilic rods, primarily from the genera Actinomyces and Propionibacterium. Both Actinomyces israelii and Propionibacterium propionicus are causative agents of human actinomycosis, occurring as part of the normal flora of the oral cavity and alimentary canal. The genera Actinomyces and Propionibacterium are defined by chemotaxonomic tests, for example, cell wall composition, fermentation products, Deoxyribonucleic acid (DNA) morphology, and ribosomal Ribonuclei acid (RNA). Actinomycosis can affect virtually any site in the body and is usually categorized into cervicofacial, thoracic, central nervous system, abdominal, and pelvic types, depending on the clinical manifestation. Thoracic actinomycosis may result from aspiration or from extension of cervicofacial or abdominal infection.3 The initial symptoms are indistinguishable from pneumonia caused by other bacteria. Pulmonary complications such as pleural effusion, pericardial effusion, fibrotic changes of lung parenchyma, and rib destruction have been reported.4–6
Diagnosing thoracic actinomycosis often poses a great challenge to the clinician due to its rarity. The initial symptoms are indistinguishable from pneumonia caused by other bacteria, and the radiological findings are often nonspecific.7 Bacteriological identification of one of the microbial agents of actinomycosis plus the microscopic finding of associated sulfur granules is usually required to confirm the diagnosis. Transbronchial and FNA biopsies are often performed to acquire tissue for such diagnosis, but these techniques are limited by the small specimen sizes provided.8 In our case, incisional biopsy was ultimately required. However, primary isolation of the organism from any specimen requires prolonged incubation in broth culture or solid medium for at least five and often 14 days. Culture is particularly difficult if the patient had been on prior treatment with antibiotics, as in our index case, as these organisms are exquisitely susceptible to antibiotics such as penicillin. Hence, a high rate of false negative results is not uncommon. Because of the diagnostic challenges, delays in diagnosis of up to a few months are not uncommon and may result in the spread of the disease to distant sites (in our case, to the chest wall).1 In our hospital, only 7 cases of actinomycosis were diagnosed in the 10 year period 1993–2002 (Table 1), and only 2 of those cases were of thoracic actinomycosis. Diagnosis was especially difficult in the case reported here, as presentation with a chest wall mass is exceedingly uncommon even for thoracic actinomycosis. Out of 37 patients presenting to our institution primarily with a chest wall mass over this 10 year period, this was the only one found to have actinomycosis. Previous reports in the literature of thoracic actinomycosis presenting primarily as a chest wall mass are rare. An index of clinical suspicion should be maintained for patients presenting with a pneumonia-like picture, refractory pleural effusion, a tender chest wall mass if initial investigations and empirical treatment are fruitless. Early specific microbiological investigation and treatment targeting actinomycosis may preclude unnecessary progression and spread of the condition.
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ABSTRACT
INTRODUCTION
