A Case of Thoracic Empyema Caused by Actinomyces naeslundii

Abstract

BACKGROUND Actinomycosis is a clinically significant but uncommon infectious disease caused by anaerobic commensals of Actinomyces species, and the incidence of thoracic empyema is rare. We report an extremely rare case of empyema caused by Actinomyces naeslundii (A. naeslundii). CASE REPORT A 39-year-old man presented to our hospital with fever and dyspnea. He had massive pleural effusion and was diagnosed with a left lower-lobe abscess and left thoracic empyema. Thoracic drainage was performed and Ampicillin/Sulbactam was administered for 3 weeks. Four years later, the patient presented with back pain, and chest X-ray showed increased left pleural effusion. After close examination, malignant pleural mesothelioma was suspected, and computed tomography-guided needle biopsy was performed, which yielded a viscous purulent pleural effusion with numerous greenish-yellow sulfur granules. A. naeslundii was identified through anaerobic culture. Thoracoscopic surgery of the empyema cavity was conducted, and Ampicillin/Sulbactam followed by Amoxicillin/Clavulanate was administered for approximately 6 months. No recurrence has been observed for 1 year since the surgical procedure. CONCLUSIONS Actinomyces empyema is a rare condition, and this case is the second reported occurrence of empyema caused by A. naeslundii. The visual identification of sulfur granules contributed to the diagnosis. Long-term antibiotic therapy plays a crucial role in treatment.

Figure 1.

Chest computed tomography (CT) images upon hospital arrival. Pre-admission chest CT showing left pleural effusion (arrow head) and a lung abscess (arrow) within the atelectasis of the left lower lobe (A). CT upon recurrence showing a mass at the site of the previous empyema cavity, along with pleural thickening and a low-attenuation area inside (B).

Figure 2.

Positron emission tomography-CT prior to CT-guided needle biopsy. Positron emission tomography-CT revealing enhanced 18F-fluorodeoxyglucose uptake in the mass, with a maximal standardized uptake value of 18.61.

Figure 3.

The specimen obtained through the second CT-guided biopsy. During the second CT-guided biopsy, viscous purulent pleural effusion was aspirated, and greenish-yellow sulfur granules were confirmed macroscopically (A). Microphotography of the sulfur granules, showing actinomycotic granules (arrow) surrounded by inflammatory cell infiltration (B) (hematoxylin and eosin stain, magnification ×20).

Figure 4.

Contrast-enhanced CT prior to the surgical procedure. Contrast-enhanced CT showing a small area of low attenuation inside the enhanced thickened pleura (arrow). The empyema cavity exhibited slight reduction compared with the plain chest CT obtained prior to the initiation of antibiotic therapy.