IE is a potentially lethal disease with a low incidence (1.7–7.9 cases/100,000 inhabitants).
C. striatum is a rare cause of IE, causing about 0.33% of all cases of IE [
4]. As a member of the corynebacteria,
C. striatum is a Gram-positive, aerobic, non-sporulating bacillus that grows slowly in cultures and is distributed in the skin and mucous membranes of normal hosts and hospitalized patients. It is one of the more commonly isolated coryneform bacteria in the clinical microbiology laboratory and is usually considered a contaminant because of its low virulence. However,
C. striatum can cause not only IE but also a variety of different infections such as pneumonia, empyema, peritonitis, arthritis, keratitis, intrauterine infections, wound infection, breast abscess, and osteomyelitis [
5]. Risk factors for
Corynebacterium endocarditis include pre-existing cardiac disease, a history of bacterial endocarditis, and the presence of prosthetic devices [
6]. Rufael et al. [
7] reported the first case of native valve endocarditis due to
C. striatum, which required a combination of medical and surgical treatments [
7]. Of the 24 cases of
C. striatum endocarditis found in PubMed (Table
1) [
6‐
30], most showed a predilection for heart valves. In our case, however,
C. striatum colonized the left atrial apex masquerading as a left atrial myxoma instead of attaching to the heart valves. Looking back on our data, there were three main potential causes of misdiagnosis. First, the patient had no classic symptoms of IE on admission. Second, both TEE and the surgical findings supported the diagnosis of left atrial myxoma. Third, the initial histopathology was misleading.
Table 1
Summarizing previously reported cases of C. striatum endocarditis
8 | 76 | M | None | Aortic | Medical | Died |
7 | 54 | M | Hypertension | Aortic | Medical and surgical | Survived |
9 | 73 | M | Pacemaker | Tricuspid | Medical and surgical | Survived |
10 | 24 | M | Ventricular shunt | Pulmonary | Medical | Survived |
11 | 68 | M | Hypertension | Mitral | Medical | Survived |
12 | 72 | F | Prosthetic valve | Aortic | Medical | Died |
13 | 62 | F | Prosthetic valve | Aortic | Medical | Survived |
14 | 50 | M | Mycotic aneurysm | Aortic | Medical and surgical | Survived |
15 | 61 | F | Rheumatic fever | Mitral | Medical | Survived |
15 | 72 | F | Prosthetic valve | Mitral | Medical | Survived |
16 | 46 | F | Hemodialysis | Tricuspid | Medical | Survived |
17 | 68 | M | Prosthetic valve | Mitral | Medical | Survived |
18 | 69 | F | Endometrial cancer | Mitral | Medical and surgical | Survived |
19 | 77 | F | None | Mitral | Medical | Survived |
6 | 62 | M | Hypertension | Aortic | Medical and surgical | Survived |
20 | 73 | F | Hypertension, chronic kidney disease, and diabetes mellitus | Mitral | Medical | Survived |
21 | 83 | M | Metastatic prostate cancer | Mitral | Medical | Died |
22 | 71 | M | Diabetes mellitus | Mitral | Medical and surgical | Died |
23 | 71 | F | Pacemaker prosthetic valve | Mitral | Medical and surgical | Survived |
24 | 62 | M | Cardiomyopathy, diabetes mellitus and osteomyelitis | Aortic | Medical and surgical | Survived |
25 | 69 | F | ANCA+ vasculitis | Mitral | Medical and surgical | Died |
26 | 51 | M | Pacemaker | Not described | Medical and surgical | Survived |
27 | 56 | M | Diabetes mellitus, chronic kidney disease, and osteomyelitis | Mitral | Medical and surgical | Died |
28 | 78 | M | Chronic kidney disease, diabetes mellitus and pacemaker | Tricuspid and right ventricular wall | Medical and surgical | Survived |
29 | 53 | F | None | Quadricuspid aortic | Medical and surgical | Survived |
The category “definite IE based on clinical criteria” involves with at least two major criteria, or one major criterion and three minor criteria, or five minor criteria. Major criteria include blood culture positive for IE, evidence of endocardial involvement, echocardiogram positive for IE, and new valvular regurgitation. According to the clinical, echocardiographic and biological findings, as well as the results of serologies, the patient did not meet the modified Duke’s criteria for diagnosis of endocarditis when he was transferred to our hospital. However, two of the major Duke criteria were met after the first operation―the positive blood culture and echocardiographic findings―enabling a definitive diagnosis [
31]. Looking back,
Corynebacterium was present in the first surgical specimen in our case. Therefore, the left atrial mass should have been considered an occult bacterial vegetation. The
C. striatum was likely completely surrounded by fibrous tissue, so the patient had no signs of infection until bacteria were released by the first surgery. Ori Elkayam et al. [
22] pointed out that IE is the most common manifestation of
C. striatum, particularly in patients with nosocomial risk factors. But it is a potential pathogen even in normal hosts with no risk factors, such as our patient. Therefore, in addition to the routine pathological examination, special stains such as Gram staining or Wright’s staining should be performed if a few macrophages are seen. When a patient with suspected myxoma develops an unmanageable fever postoperatively, physicians should be alert to the progress of IE and evaluate the possibility with a combined pathological examination and blood cultures. The pathological examination of resected tissue or embolic fragments remains the gold standard for the diagnosis of IE. Nevertheless, we fell into a trap in this case because no pathogens were found in the first or second surgical specimens on examination with a medical microscope at a 400× magnification (Fig.
2f). We confirmed that
C. striatum in positive blood cultures was responsible for the IE and that this diagnosis was supported by the results of Gram staining and Wright’s staining of tissue specimens viewed at a 1000× magnification with an oil immersion lens. Daptomycin is an effective drug for
C. striatum and has been used in some patients with endocarditis caused by this organism [
28]. Combined antibiotic treatment and surgery were performed because of the uncontrolled infection and severe aortic regurgitation based on the ESC guidelines [
32]. The patient had a slow, uneventful recovery.