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A 54-year-old African-American woman presents to her primary care physician's office with a history of right-sided chest discomfort and intermittent dry cough of 4 weeks' duration. She denies having a fever, chest pressure, night sweats, hemoptysis, or weight loss. However, she does admit to a 25–pack-year history of smoking and denies using any illicit drugs. She has not recently traveled outside the United States.

On physical examination, she is afebrile with a normal heart rate and blood pressure. She is a well-developed, thin woman who appears to be in no apparent distress. Findings from the patient's lung and heart examination are unremarkable. Findings from the remainder of the examination are also unremarkable.

The chest radiograph (see Image 1) demonstrates a cavitary mass in the right upper lobe of the lung. Follow-up chest CT (see Image 2) shows the same cavitary mass as a thick-walled lesion in the posterior segment of the right upper lobe. It measures 4.2 X 5.5 cm.

The patient is initially given a 2-week course of oral clindamycin. However, follow-up chest images obtained approximately 1 month afterward fail to reveal any interval improvement. A positron emission tomographic (PET) scan is subsequently obtained and shows abnormal [18F]-fluorodeoxyglucose (FDG) uptake in the right posterior and apical segments of the right upper lobe and right hilar lymph node with no other foci of abnormal uptake. Ultrasonography-guided aspiration and core lung-mass biopsy are performed, but the results are nondiagnostic.

The patient eventually undergoes thoracotomy and right upper lobectomy. Biopsy specimens are obtained. The pathology specimen shows evidence of acute necrotizing bronchopneumonia and a cavitary abscess. Silver staining demonstrates aggregates of filamentous organisms (see Image 3).

What is the organism, and what is the diagnosis?


Pulmonary actinomycosis: Before the pathology specimen was obtained, tuberculin skin testing, sputum analysis for acid-fast bacilli, and routine cultures were also ordered; all findings were negative. Additional laboratory studies, including a serum creatinine determination, yield normal levels. HIV serology also returned a negative result. The stain shown in Image 3 demonstrates aggregates of filamentous organisms highlighted with silver stain. This pattern is consistent with actinomyces, and pulmonary actinomycosis is diagnosed.

The differential diagnosis of a cavitary lung mass consists of a wide variety of pulmonary diseases. Some, such as bronchogenic carcinoma, tuberculosis (TB), and suppurative lung disease, are common, and others, such as actinomycosis, are relatively infrequent.

On clinical evaluation, pulmonary actinomycosis is commonly confused with TB, suppurative lung disease, and malignancy. Patients with pulmonary actinomycosis usually present with a pulmonary consolidation. However, as in this case, some patients present with cavitation and spread to the adjacent tissues. Bronchoscopic findings are usually nondiagnostic, and most patients require open lung biopsy. The organism involved in this condition is Actinomyces israelii. This microorganism is slender, branching gram-positive bacillus embedded in the matrix of the sulfur granules. The hallmark of actinomycosis is the formation of the yellow sulfur granules.

The optimal duration of treatment is not clearly established, and the traditional recommendation of intravenous antibiotic therapy (beta-lactam) for 2-6 weeks followed by oral antibiotic therapy for 6-12 months is not always necessary. The condition is best treated with individualized therapeutic protocols depending on factors such as the initial burden of disease, the patient's response to and the success of surgical resection, and the patient's progressive clinical and radiologic response to continuing antibiotic regimens. The most common indications for surgery are hemoptysis and empyema. As a complication, chronic sinus drainage has become decreasingly frequent, presumably because of the widespread use of the antibiotics.

The patient in this case responded well to antibiotic therapy continued postoperatively. She completed a 6-month course of amoxicillin with no clinically significant adverse effects. During follow-up, a repeat chest CT scan showed no evidence of active disease.

Link to further Information on:

For more information on pulmonary actinomycosis, see the eMedicine articles Actinomycosis (within the Pediatrics specialty), Actinomycosis (within the Internal Medicine specialty), and Pulmonary Angiography (within the Radiology specialty).