Atrial giant cell myocarditis with preserved left ventricular function: a case report and literature review

Giant cell myocarditis (GCM) is a rare and fatal inflammatory disorder induced by T-lymphocytes, typically affecting young adults [1]. Generally, this disease presents with a rapidly progressive course and a very poor prognosis. GCM is characterized by acute heart failure, ventricular arrhythmias, and varying grades of atrioventricular block. Uncommon findings, including pericardial tamponade and atrial masses, have been previously reported in GCM cases. As its clinical presentation of overlap with other cardiac diseases, the imaging features are nonspecific, and due to its rarity, the timely diagnosis of GCM is challenging and the definite diagnosis relies on the endomyocardial biopsy (EMB). Although the underlying pathophysiological mechanisms of GCM remain elusive, statistics show that up to 20% of GCM cases are associated with other autoimmune diseases, indicating that altered immunity may be a causal factor [2]. In recent years, atrial GCM (aGCM) has been recognized as a clinicopathological entity distinct from classical GCM [3]. As described by retrievable case reports, although its histopathological manifestations are highly similar to those of classical GCM, this entity is characterized by preserved left ventricular function and atrial arrhythmias, without ventricular arrhythmias [3‐10]. aGCM tends to show benign disease progression with a better clinical prognosis compared with the rapid course and poor prognosis of vGCM. The atrial myocardium is not routinely sampled at autopsy or during routine pathology, thus, knowledge of the atrial myocardium originates only from retrospective case descriptions, making its diagnosis challenging [7]. We report a patient with aGCM with a history of renal abscess whose persistent myocardial injury considered to be associated with a history of renal abscess. Infection could be a potential trigger for the development of aGCM in this patient. An extensive review was also performed and the following three aspects were summarized: (1) Epidemiology and histopathological characteristics of aGCM; (2) The role of imaging in the evaluation of aGCM; (3) Diagnostic points and therapeutic decisions in aGCM.

A 39 year-old man was admitted to our hospital in January 2022 because of a week-long history of palpitations. In March 2018, the patient had been admitted to our hospital because of recurrent fever for one month and pyuria for ten days. Laboratory tests showed an increased level of neutrophils (84.2%, normal: 40–75%), decreased lymphocytes (11.5%, normal: 20–50%), decreased red blood cells (3.42 × 10¹²/L, normal: 4.0–5.5 × 10¹²/L), decreased hemoglobin (80 g/L, normal: 120–160 g/L), markedly increased C-reactive protein (CRP) (356.9 mg/L, normal: < 10 mg/L), elevated serum amyloid protein(139.6 mg/L, normal: < 10 mg/L), increased erythrocyte sedimentation rate (ESR) (80 mm/h, normal: < 20 mm/h), and elevated fibrinogen (7.42 g/L, normal: 2.0–4.5 g/L).; urine microscopy showed an increased leukocyte count (25–30/HP, normal: < 5/HP), while urine bacterial culture was negative. Computed tomography (CT) examination displayed massive bilateral perinephric exudate and swelling of the renal pelvis and calyx wall with both rough upper ureters. During the hospitalization, the patient had fever around 2–4 pm every day, with the highest temperature of 38.5 °C. We organized several expert consultations and made several revisions to the medication regimen. (1st: Paracetamol + Levofloxacin; 2nd: Imipenem + Amikacin; 3rd: Fluconazole + Meropenem + Fosfomycin), whereas the improvement was unremarkable. CRP level (99.3 mg/L) significantly decreased, while it was still higher than normal level. A subsequent urine culture revealed the growth of Candida tropicalis, the 4th modification was applied to the medication regimen (Linezolid + Fosfomycin). After that, the body temperature returned to normal and the urine culture was negative. After one week of stabilization, treatment was changed to Linezolid + Ofloxacin. The patient was subsequently discharged. As the kidney condition was complicated and the cardiac symptoms were not prominent at that time, no comprehensive cardiac examination was performed. Only an enlarged left atrium and a small amount of pericardial effusion were found on echocardiogram during admission, which was not taken seriously by the clinician. The patient's electrocardiogram (ECG) at admission and discharge were both normal.

In 2022, the patient was admitted to our hospital with cardiac symptoms. Tachycardia-bradycardia syndrome was detected on dynamic ECG. The ECG (Fig. 1A) revealed junctional escape-sinus capture bigeminy. Although the slowest heart rate was not captured on this ECG, 24 h bedside monitoring revealed a tachycardia-bradycardia syndrome, with a heart rate of 140 beats/minute during atrial flutter and a heart rate of only 40 beats/minute during bradycardia. Based on the patient's clinical symptoms and electrocardiographic abnormalities, the diagnosis of sick sinus node syndrome (SSS) was considered. The echocardiogram (Fig. 2) revealed a space-occupying lesion with moderate echogenicity located in the right atrium, measuring approximately 55 × 30 mm in size, bi-atrial enlargement, tricuspid regurgitation (mild-moderate), and a small amount of fluid in the pericardial cavity, while left ventricular ejection fraction (67%), and segmental motion of the ventricular wall were both normal. Cardiac CT (CCT) revealed multiple nodules and masses in the right atrial wall, peri-coronary artery, and left side of the inferior vena cava (Fig. 3). CRP (27.3 mg/L, normal; < 10 mg/L), ESR (40 mm/h; normal: < 20 mm/h),Serum B-type natriuretic peptide (133 pg/ml; normal < 100 pg/ml), fibrinogen (6.25 g/L; normal 2–4 g/L), immunoglobulin G (IgG)-LAMBDA light chain (2.73 g/L; normal 0.9–2.1 g/L), KAPPA light chain (5.20 g/L; normal 1.7–3.7 g/L), and IgG4 (2.545 g/L; normal 0.03–2 g/L) levels were elevated. No clinical evidence of other autoimmune diseases was found. Moreover, examinations of potentially pathogenic agents, including antibodies to syphilis spirochetes, human immunodeficiency virus, hepatitis A, B, and C viruses, and mycobacterium tuberculosis, were all negative. The results of autoimmune antibody testing demonstrated negative for the following antibodies: anti-Scl-70 antibody, anti-mitochondrial antibody, anti-PCNA antibody, anti-nucleolar antibody, anti-Jo-1 antibody, anti-histone antibody, anti-U1-nRNP antibody, anti-centromere antibody, anti-SS-A antibody, anti-SS-B antibody, and anti-Sm antibody. The levels of anti-smooth muscle antibody (9.90 U, normal: 0–22 U), anti-nuclear antibody (11.1 U/ml, normal: 0–55 U/ml), anti-double stranded DNA antibody (23.95 IU/ml, normal: ≤ 200 IU/ml), anti-glomerular basement membrane antibody (2.4 Units, normal: 0–20 Units), and anti-intrinsic factor antibody (4.4 Units, normal: 0–22 Units) were all within the normal range. Due to the friable texture of the inflammatory mass, we were concerned that the mass could easily fragment after EMB and lead to severe complications such as embolism. Furthermore, the size of the right atrial mass made it difficult to pass through the tricuspid valve, increasing the risk of injury and embolism. Therefore, we opted for cardiac tumor resection instead of EMB. Other than aGCM, our suspected diagnoses of this patient before surgery included atrial myxoma, atrial malignant tumor (primary or metastatic), and IgG4 related disease (Table 1). Four days after admission, cardiac tumor resection was conducted (Fig. 4). However, during the surgery, we found that the lesion was scattered and multifocal, making it impossible to remove completely. Therefore, only a biopsy was performed to remove the atrial mass and part of the pericardium by wrapping the lesion tissue on the surface of the right atrium. The histopathological examination (Fig. 5) of resected tissue (size: 0.8 × 0.8 × 0.4 cm³) revealed large areas of myocyte replacement by hyperplastic fibrous tissues and inflammatory cell infiltrate composed of T-lymphocytes, plasma cells, eosinophils, and scattered multinucleated giant cells, which was consistent with the pathological features of GCM. Immunohistochemical results documented the lymphocytic infiltrate with CD3+ and CD5+ T lymphocytes, fewer CD20+ B lymphocytes, scattered CD68+ histiocytes and giant cells, without IgG4+ plasma cells. No bacteria, such as acid-resistant bacilli, fungi, or other parasites were found, and no foreign body was detected. After the surgery, the patient developed atrial flutter (140–180 beats/minute), accompanied by bradycardia (38 beats/minute). In addition, the patient had a symptom of chest tightness. Due to the complexity of the condition, temporary transvenous pacing (VVI mode) was performed to maintain the heart rate. Considering that the patient may benefit from anti-inflammatory treatment, he received continuous intravenous infusion of methylprednisolone for five days (80 mg daily), followed by a combination of methylprednisolone (40 mg daily) and cyclosporine (50 mg twice daily). However, after ten days of pharmacological intervention, there was no improvement in the arrhythmia, and thus a dual-chamber permanent pacemaker (DDD mode) was implanted. After permanent pacemaker implantation, the patient was treated with immunosuppressive therapy including methylprednisolone (24 mg once daily) and cyclosporine (50 mg twice daily). At outpatient follow-up one month after starting the immunosuppressive therapy, the patient reported significant symptom relief. Subsequently, the dosages of methylprednisolone and cyclosporine were gradually reduced. The total duration of immunosuppressive therapy after permanent pacemaker implantation was six months. At present, the patient continues to do well.

GCM is an uncommon disorder that was first explored in 1905 [14]. According to autopsy reports from Japan, the United Kingdom, and India, its incidence ranges from 0.007 to 0.051% [15, 16]. Compared with typical ventricular GCM (vGCM), aGCM is a rarer pathological entity of GCM that mainly affects the atria. aGCM was first reported by McCrea in 1964 [9]. The first reported aGCM patient had a history of rheumatic fever and rheumatic mitral valve disease. aGCM was regarded as an incidental finding during his elective mitral valve replacement. As no evidence of infection was found in this patient and no typical rheumatic lesions were present in his left auricle lesion, he was diagnosed with chronic GCM of unknown origin. To date, the lack of familiarity still exists in the current knowledge regarding this entity. We retrieved a total of 15 aGCM patients (median age of 53 years,7 male cases) on PubMed and Medline online databases, of whom 9 cases were discovered unexpectedly during elective valve surgery, 1 case was discovered unexpectedly during coronary artery bypass grafting, 4 cases with acute heart failure(HF) underwent diagnostic atrial biopsy, and 1 case died of other causes and his asymptomatic aGCM lesions were found incidentally at autopsy [3‐10]. The above findings suggest that aGCM is more common than we thought.

Multiple circulating autoantibodies, some of which are cardiac-specific, have shown to play a key role in the progression and induction of myocarditis [17, 18]. These autoantibodies are directed against different autoantigens that are mainly unrestricted when exposed to the myocardium. However, in the presence of immune abnormalities, these autoantigens are attacked by autoantibodies, leading to autoimmune diseases. The exact mechanisms of how these autoantibodies persist or even induce cardiac-specific autoimmune responses have not been fully understood. Endogenous (immunocompromised) or exogenous factors (infections), molecular mimicry and cross-reactivity may play an important role in the induction of cardiac autoimmune responses [3, 19, 20]. aGCM and vGCM have overlapping pathogenesis, both are autoimmune diseases, and have genetic susceptibility. However, aGCM is distinguished from typical vGCM, and the presence of atrial-specific antigens may be involved in the development of aGCM [3, 21].

Although aGCM more or less involves the ventricles, it mainly affects the atria. The most common sites of aGCM are the left atrial appendage and the left atrium, followed by the right atrial appendage, the right atrium, and the walls of the blood vessels surrounding the heart, while a single site is not mainly involved [3‐5, 10, 22]. T lymphocytes and characteristic multinucleated giant cells infiltrating the atria are the histopathological features of aGCM [23]. T lymphocytes mainly include CD3+ and CD8+ T lymphocytes. Additional inflammatory cells include eosinophils, plasma cells, B cells, and histiocytes. aGCM in the acute inflammatory phase can cause myocardial hypertrophy and myocardial necrosis [7]. As persistent myocardial inflammation in aGCM moves from the acute to the chronic phase or further develops into chronic inflammatory cardiomyopathy, histopathological examination may show less inflammatory infiltrates, primarily fibrosis [23]. Reduced atrial systolic function, poor blood return, abnormal valve function, and atrial arrhythmias in aGCM promote the formation of appendage thrombus.

Diagnostic criteria for clinically suspected myocarditis could be summarized as follows [20]:

EMB is the only available method to confirm the diagnosis of myocarditis [47]. However, during EMB procedures, atrial tissue is not routinely sampled, which, together with inflammatory damage in aGCM more or less involving the ventricles, makes it difficult to distinguish aGCM from vGCM [21]. Therefore, Atrial tissue sampling should be performed in patients with suspected myocarditis who have clinical features of aGCM.

Based on the available case reports (including our case), we conclude that the diagnosis of aGCM requires evidence of myocardial pathology and clinical signs. Patients with typical myocardial pathological evidence of preserved left ventricular function with atrial arrhythmias or SSS should be diagnosed with aGCM, whereas those with ventricular HF with decreased ejection function cannot be diagnosed with aGCM.

The aim of treatment is to reduce cardiac symptoms, in order to improve patients’ quality of life. The treatment of aGCM includes the following aspects:

It is broadly accepted that aGCM is a rare disease with a very low prevalence, whereas its true incidence appears to be greatly underestimated based on the lack of non-invasive and highly specific diagnostic methods, the typical overlap of symptoms with other more common/occasional cardiovascular diseases, and the fact that atria are not routinely sampled in EMB.

Autoimmune diseases, infections, genetic susceptibility, immune depression, molecular mimicry, and cross-reactivity may be risk factors for the triggering and development of aGCM. The case reported in the present study also indicated that aGCM is triggered and developed by fusion of endogenous and environmental (infectious) factors. However, our knowledge about aGCM is based on retrospective case reports and the lack of clinical and experimental animal models is noteworthy, which makes clarifying the specific triggers and causative factors for aGCM progression remains a challenge. With the development of imaging techniques, the integration of echocardiography, ECG, CCT, CMRI, and nuclear imaging can facilitate understanding the histopathological features of aGCM, thus helping to make diagnostic and therapeutic decisions. Nevertheless, EMB remains the diagnostic gold standard for etiology and differential diagnosis. Therefore, atrial tissue sampling should be performed during EMB procedures in highly suspected patients with aGCM. The therapeutic knowledge suggests that timely symptomatic and supportive treatment is effective for aGCM, while the recommendation of immunosuppressive therapy for aGCM should be assessed in specific clinical settings. As a pathological entity distinct from classical vGCM, aGCM has a relatively slow progression and good outcome without directly leading to fulminant death. In addition, atrial-specific antigens may be closely associated with triggering and maintaining the aGCM-specific autoimmune process, while further research is required to determine which antigens play an important role in the pathogenic mechanism.