To our best knowledge, this is the first case report of pulmonary actinomycosis attributable to A. meyeri presenting as cardiac tamponade.In our patient, the pericarditis seemed to be caused by the direct extension of the inflammation from pulmonary actinomycosis, because we could not detect any microorganisms in the patient’s pericardial fluid. The arrhythmia which suddenly occurred in our patient and did not recur after the penicillin therapy suggests cardiac actinomycosis, however, evidence was not obtained.
Cardiac actinomycosis is very rare, and the frequency of this condition was reported as only 1.2 to 2% of all cases of actinomycosis [
11,
12]. Cardiac actinomycosis was first reported in 1884 [
13], and to date, two comprehensive reviews about this condition have been published. Cornell et al. documented 68 cases of cardiac actinomycosis and Fife et al. detailed 19 cases of pericardial actinomycosis documented [
11,
14]. Cardiac involvement was usually caused by the direct extension of thoracic disease [
15,
16]. In fact, it was reported that 23 out of 29 cases (79%) of pericardial actinomycosis since 1950 had thoracic involvement [
17]. It is characterized by involvement of the pericardium, myocardium, and endocardium in a decreasing order of frequency, which is consistent with its mode of contiguous spread through tissue planes from the thorax [
18]. Our patient had pulmonary lesions as primary sites of infection, and the pericardial involvement seemed to be caused by the direct extension from the primary sites However, in our patient, pericardial fluid did not show the evidence of
A. meyeri infection. Actually, the diagnosis of actinomycosis is generally hampered by the difficulty in isolation and culture of the organism. It must be cultured in strictly anaerobic conditions. In the review of Fife et al., purulent pericardial fluid was obtained from 10 (53%) of 19 cases, however,
Actinomyces species were successfully cultured from the fluid in only two of those 10 cases [
14]. Similarly, low yields (26%) of biopsy specimen cultures have been observed [
14]. Sulfur granules, long regarded as a histological hallmark of actinomycosis, are very strongly suggestive of the diagnosis. However, they are not entirely specific to actinomycosis, since these granules can also be found in nocardiosis, botryomycosis, aspergillosis, and coccidioidomycosis [
4,
19]. Fortunately, gram stain of the purulent fluid obtained by pneumocentesis showed Gram-positive filamentous rods, and cultures from the purulent fluid grew
Actinomyces species. Finally, the genetic testing with a method for clone library sequencing of the 16S rDNA gene of the fluid revealed
A. meyeri along with
Fusobacterium species. It was reported that two-thirds of the infections with
A. meyeri were polymicrobial [
8], and it was thought that reduced oxygen tension and inhibition of phagocytes induced by concomitant bacterial infections might enhance the pathogenicity of
Actinomyces species [
9].
In patients with cardiac actinomycosis, the prognosis is good when correct diagnosis and medical treatment are made, and appropriate choice of antibiotics and pericardial drainage are important. It was reported that when the diagnosis of cardiac actinomycosis was given and appropriate antibiotic therapy was started, 86% of patients survived [
17]. The recommended antibiotic therapy is high doses of intravenous penicillin G (12–20 MU/d in divided doses) for 4 to 6 weeks, followed by 6 to 12 months of oral penicillin/amoxicillin [
20]. Alternative choices in patients allergic to penicillin are sulfonamide, tetracycline, erythromycin, or third-generation cephalosporin.
A. meyeri is also susceptible to most antibiotics, and penicillin remains the most cost-effective drug. The associated bacteria are generally susceptible to the antibiotics for the treatment of
A. meyeri. According to the previous reports, a pericardial drainage or pericardiectomy was required in 82 and 45% of surviving patients, respectively. Our patient was successfully treated by pericardial drainage, pneumocentesis, and antibiotics.