Actinomycosis is a chronic infection caused by gram-positive anaerobic bacteria of the Actinomyces genus that are normally saprophytic colonizers of the oral cavity and gastrointestinal and urogenital tracts. Dissemination is generally hematogenous.1 Unlike other Actinomyces species, Actinomyces meyeri (A. meyeri) can cause lung infections, although empyema caused by this strain is very rare. Actinomycosis is characterized by the development of fistulae in affected tissues and suppuration containing sulfur granules, and it is technically difficult to culture.

We report a case of empyema caused by A. meyeri recently treated in our hospital. Our patient was a 62-year-old man, smoker of 40 pack-years and alcohol consumption of 18 units/day, with severe neurosensory hypoacusia resulting from meningitis in his adolescence. He presented in the emergency department of our hospital with a 3-week history of left pleuritic pain, non-productive cough, a sensation of dysthermia, and unexplained weight loss. He was hemodynamically stable and afebrile, with normal breathing in room air. Physical examination revealed halitosis due to septic mouth with several missing teeth, reduced vocal fremitus throughout the left hemithorax and dullness on percussion, and hepatomegaly of 2 finger breadths.

Clinical laboratory tests showed: red blood cells 3.77×106/μL, hemoglobin 11.5g/dl, hematocrit 33.9%, MCV 100, leucocytes 8.87×103/μL (85% neutrophils), sedimentation rate 120, total bilirubin 2.4mg/dl (direct 1.9mg/dl), GOT 114IU/l, GPT 129IU/l, GGT 280UI/l and alkaline phosphatase 245IU/l. Arterial blood gases (room air): pH 7.51, pCO2 33.1mmHg, pO2 69.5mmHg. Chest radiograph showed an apparently homogeneous increase in density occupying most of the left hemithorax, with a well-defined, convex upper border, that did not move when the patient was placed in lateral decubitus. Abundant left hyperechogenic pleural effusion with internal septa was observed on chest ultrasonography. Purulent fluid was obtained by thoracocentesis, showing pH 6.80, leukocytes 173×103/μL (75% neutrophils), glucose 15mg/dl, LDH 20,000UI/l, proteins 4.7g/dl, C-reactive protein 9.88mg/dl, procalcitonin <0.020ng/mL, interleukin-6 152,525pg/ml and adenosine deaminase 227U/l. A diagnosis of empyema was reached, and empirical antibiotic treatment began with i.v. amoxicillin/clavulanic acid 2g every 8h, chest tube (16F; 9 days), and intrapleural urokinase (100,000IU/day, 3 days). Progress was favorable. Blood cultures were negative. Culture of pleural fluid for mycobacteria was negative, and anaerobic culture for A. meyeri was positive.

Two months later, the patient remains asymptomatic, and continues to receive oral amoxicillin (500mg/8h). Chest computed tomography shows pleural thickening throughout the lateral and posterior region of the left hemithorax with a minimum amount of associated pleural fluid.

Pleural infection with A. meyeri is very rare, and to date, only 12 cases have been published in the literature (Table 1).2–12 Poor oral hygiene and alcoholism, as presented by our patient, are predisposing factors, since the bacteria reaches the pulmonary parenchyma via aspiration from the oral cavity. The pleura becomes involved either from contiguity or hematogenous dissemination.1,13 Patients are usually men (11/13 cases; 84.6%), over 40 years of age (12/13; 92.3%), other organs in addition to the pleura may be involved (generally the lung), and fistulization may occur. Pleural fluid shows typical features of empyema: high LDH and leukocyte values (generally neutrophils), and low pH and glucose. Some cases may also involve high levels of adenosine deaminase and low proteins.14

The disease may coexist with lung cancer, since A. meyeri tends to colonize the necrotic tissue that often occurs with malignancy.15 In the absence of characteristic sulfur granules in pus from the infected tissue, isolation in sputum can be a sign of simple colonization. In such cases, isolation of A. meyeri is of little diagnostic interest. In contrast, A. meyeri cultured in pleural fluid is the basis for the diagnosis of infection, and care should be taken to use appropriate anaerobic media. Treatment of choice is amoxicillin/clavulanic acid or penicillin G sodium (administered intravenously for 2–6 weeks, followed by oral amoxicillin for 6–12 months), depending on clinical and radiological progress. Other alternatives are clindamycin, doxycycline or erythromycin, if the patient has penicillin allergy or intolerance.7 A chest tube and intrapleural fibrinolytics are generally required, and occasionally pleural decortication can be a last resort.14 Progress is usually favorable, although one case of death has been reported.2 Residual diffuse pleural fibrosis is a possible sequela. Our patient has only been receiving treatment for 2 months, but his clinical response appears to be favorable, pending evaluation of the possible sequela of his residual left pleural thickening with lung function testing.

The take-home message from this case is that when faced with slow-progressing pleural effusion that does not respond to standard antibiotics in a patient with known risk factors, cultures in the appropriate media should be performed to rule out empyema caused by A. meyeri.