Actinomycosis is a chronic suppurative infection due to filamentous, gram-positive, nonspore forming, anaerobic bacteria of the genus Actinomyces. Actinomyces species are commensals of the human oropharynx, gastrointestinal tract, and female genitalia. Actinomycosis is caused mainly by Actinomyces israelii.1 The organism, Actinomyces, was initially misclassified as a fungus. The word actinomycosis was derived from the Greek terms aktino, which refers to the radiating appearance of a sulfur granule, and mykos, which labels the condition a mycotic disease.2
Actinomycosis occurs worldwide. The reported incidence is approximately 1 out of 300,000 people per year. Most series describe a peak incidence in the fourth and fifth decades.1 The disease is classically divided into 3 types depending on the anatomic site involved: cervicofacial, abdominopelvic, and thoracic. Thoracic actinomycosis typically presents as an intrapulmonary infection and accounts for 15% to 20% of the total burden of disease.3 Endobronchial actinomycosis is rare. A critical component in the pathogenesis is disruption of the mucosal barrier, thereby allowing invasion of the microorganisms from aspirated oropharyngeal secretions.3
Thoracic actinomycosis, in the preantimicrobial era, was reported to extend to the ribs and chest wall causing cutaneous fistulas discharging sulfur granules.1 However, the mode of presentation has now changed with symptoms and physical signs being nonspecific and the disease being commonly confused with lung cancer, pulmonary tuberculosis, fungal infections, nocardiosis, and poorly responding pneumonia.4,5 In endobronchial actinomycosis, the most commonly reported symptoms include cough, sputum production, fever, and hemoptysis.
Rare cases of endobronchial actinomycosis have been reported in association with broncholithiasis, aspirated foreign objects, and without the presence of foreign material.6–9 In a series of 5 patients, in which the diagnosis of bronchogenic carcinoma was suspected, endobronchial actinomycosis was documented without associated broncholithiasis or aspirated foreign objects. Flexible bronchoscopy revealed an obstructive endoluminal mass, often yellow in color, in all patients.10
Endobronchial actinomycosis associated with broncholithiasis likely results from secondary colonization of a preexisting endobronchial broncholith by aspirated Actinomyces organisms with the subsequent inflammatory process enlarging the endobronchial lesion and progressively obstructing the airway.6 In a series of 9 patients, CT of the thorax revealed a proximal endobronchial calcified nodule in all patients and distal postobstructive pneumonic consolidation of the involved lobe or segment in 8 patients.6 Endobronchial actinomycosis has also been reported in association with aspirated chicken bones, a fish bone, teeth, and grape seeds.7 In a review of 11 cases, an obstructive endoluminal mass was found endoscopically in all cases. However, the foreign body was not always detected immediately but subsequently visualized on repeat bronchoscopy 3 to 4 months after initiation of antimicrobial therapy.7
Actinomycosis is a diagnostic challenge with the disease being suspected in <7% of patients who are found to have the infection.1,3 Even when the clinical suspicion is high, microbiological confirmation remains difficult. Physiological saline solution, commonly used for bronchoalveolar lavage, has been reported to inhibit growth of Actinomyces species.2 Following proper technique in collecting and delivering specimens for anaerobic culture is critical. Actinomyces stain in tissue with Gomori methenamine silver. Histopathology reveals acute inflammation surrounded by fibrosing granulation tissue. Sulfur granules, round or oval basophilic masses with a radiating arrangement of eosinophilic clubs on the surface, are highly suggestive but not pathognomonic for actinomycosis.2 Transbronchial biopsy may distort the morphologic appearance of sulfur granules. Correlation of clinical, radiologic, and pathologic findings with appropriate response to antimicrobial therapy is imperative for accurate diagnosis.
Antimicrobial treatment of thoracic actinomycosis has been based on extensive clinical experience rather than randomized controlled trials. The typical treatment consists of 2 to 6 weeks of intravenous penicillin followed by oral therapy for 6 to 12 months. Tetracycline (for penicillin allergic patients), erythromycin (for pregnant women), and clindamycin are suitable alternatives.11 A retrospective case series revealed that a substantial proportion of patients with thoracic actinomycosis can be successfully treated with <3 months of antibiotic therapy.11 In addition, a patient with endobronchial actinomycosis secondary to an aspirated fish bone achieved complete clinical and radiologic recovery after removal of the foreign body and a 1-month course of oral amoxicillin.12 Treatment for endobronchial actinomycosis must be individualized based on the initial burden of disease, performance of bronchoscopic removal of the causative foreign body, and the clinical and radiologic responses to therapy but likely does not require traditional long-term antimicrobial therapy.
In conclusion, this case is unique in that it is the first reported case of endobronchial actinomycosis associated with a covered nitinol endobronchial stent. It also highlights the importance of mucosal barrier disruption in the pathogenesis of endobronchial actinomycosis. Nitinol, an intermetallic alloy of nickel and titanium, exhibits good biocompatibility and was an unlikely contributor to the development of actinomycosis.13 Rather, the presence of the endobronchial stent contributed to disruption of the mucosal barrier with the development of inflamed granulation tissue. Therefore, despite the susceptibility of Actinomyces to penicillin, antimicrobial therapy alone would not have been adequate to achieve complete resolution. Removal of the foreign body, the covered nitinol endobronchial stent, was necessary so that the protective mucosal barrier could regenerate, eliminating the nidus for recurrent infection. In addition, it demonstrates that one must be cognizant that endobronchial actinomycosis can mimic bronchogenic carcinoma and cause FDG hypermetabolism on PET-CT. It highlights that short-term oral penicillin, opposed to long-term antimicrobial therapy, in combination with bronchoscopic removal of the stimulus for infection, is a successful treatment modality for endobronchial actinomycosis associated with a foreign body. Finally, it emphasizes the importance that pulmonologists must now recognize actinomycosis as a potential cause of endobronchial disease in patients with endobronchial stents.
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Keywords:© 2012 Lippincott Williams & Wilkins, Inc.
endobronchial actinomycosis; covered endobronchial stent; thoracic actinomycosis; foreign-body aspiration