**2. Etiology**

40 Myocarditis

autoimmune response of body through the effects of lymphocytes, natural killer cells,

Diagnosis of acute myocarditis can be difficult owing to the lack of accepted and standardized criteria in addition to the nonspecific pattern of clinical presentation. The other issue hampered agreement on the most proper diagnostic criteria and documentation of cases, is broad diversity of aetiologies associated with myocarditis (Dec et al, 1985). At present, diagnosis has been made by use of pathological classification, commonly referred to as Dallas criteria (Aretz et al, 1987). The identification of inflammatory infiltrate with or without myocardial cell necrosis on conventionally stained myocardial tissue biopsy specimens is essential for histological diagnosis. On the basis of these criteria, myocarditis is described as active or borderline myocarditis in accordance with the presence or absence, respectively, of myocardial necrosis. The inflammatory infiltrate should be further identified as lymphocytic, eosinophilic or granulomatous (Figure 1). Sampling error, low sensitivity and specificity, discrepancy in expert interpretation remain limitations to the use of endomyocardial biopsy for diagnosis of acute myocarditis (Hauck et al, 1989 & Shanes et al, 1987). Inflammation in acute myocarditis may be focal, therefore it is challenging to biopsy the inflamed area of myocardium (Robinson et al, 2005). Additionally, it is invasive and potentially dangerous procedure, particularly in the paediatric patient (Checchia & Kulik, 2006). According to the some researchers (Parillo, 2001), this histopathological criteria could not be considered the gold standard for diagnosing acute myocarditis. Molecular pathological analyses, such as polymerase chain reaction (PCR) and in-situ hybridization allows rapid detection and documentation of the viral genetic material in the myocardium (Angelini et al, 2002 & Bock et al, 2010). In 2008, it was reported that immunohistological signs of myocarditis has been associated with poor outcome in myocarditis (Kindermann et

Fig. 1. The pathological diagnosis of viral myocarditis necessitates the manifestation of a inflammatory infiltrate associated with myocyte necrosis. The infiltrate consists of

Text and image courtesy of Ragip Ortac, Gulden Diniz, Malik Ergin)

predominantly mononuclear cells (Stained by hematoxylin and eosin, magnification X 400;

Therapy of myocarditis in children with inotropes and afterload reduction is usually sufficient. Although the long-term sequels are rare, dilated cardiomyopathy and sudden cardiac death may develop in clinical course. Extracorporeal membrane oxygenation and mechanical ventilations are other options for severe cases (Vashist & Singh, 2009). Newer therapeutic strategies such as intravenous immunoglobulin and immunosuppressive agents

cytokines and apoptotic cell death (Kawai, 1999).

al, 2008).

The vast majority of myocarditis in the developed countries result from viral infections (Table 1). The causes other than infections are autoimmune-systemic diseases, toxins and hypersensitivity to drugs (Brodison & Swann, 2001). Enteroviruses (particularly Coxsackie) and adenovirus were recognized as the major cause of viral myocarditis (Baboonian& Treasure, 1997; Pauschinger et al, 1999). During the last decade, parvovirus B19 (PVB19) and human herpesvirus 6 (HHV6) have been described as new pathogens (Kuhl et al, 2003). Moreover, investigators from Germany found that PVB19 and HHV6 are the most common causes of biopsy-confirmed viral myocarditis (Kuhl et al, 2005 & Mahrholdt et al, 2006). An investigation analysing the potential role of PVB19 in the clinical setting of acute myocarditis revealed that PVB19 was the most common agent. Kuhl et al had also noticed that Dallas criteria was frequently negative in patients with positive PVB19 PCR and macrophages were augmented in virus positive cases (Kuhl et al, 2003). These findings support the postulation of Bowles et al that different viruses have various pathogenic mechanisms such as lymphocyte-dependent vs. macrophage-dependent (Bowles et al, 2005). Nevertheless, PVB19 DNA has also been revealed in the myocardium of healthy donors (Donosa et al, 2005), in hearts of adults with dilated cardiomyopathy (Lotze et al, 2004), and in hearts of the patients with lupus and amyloidosis (Kuethe et al, 2007), despite the number of subjects studies was small. From these results, the question arises whether PVB19 certainly cause the underlying heart disease or whether it is just spectator attending in the heart as a result of former infection which is usual in young adults or children. A study by Kuethe et al was conducted to investigate this question. They suggested that PVB19 displays lifelong persistence, identification of PVB19 DNA was not correlated with clinical symptoms and serological analysis should be standardized procedure for future studies considering prevalence of PVB19 (Kuethe et al, 2009).

Polymerase chain reaction (PCR) analyses of myocardium in children and adult patients have showed the existence of adenoviral genome in cases with myocarditis and dilated cardiomyopathy with a larger frequency than enterovirus (Pauschinger et al, 1999 & Bowles et al, 2003). Geographical variation in viral etiology is also remarkable that hepatitis C virus has been more commonly documented in Japanese patients and parvovirus B19 is more frequently detected by PCR in German population (Magnani & Dec, 2006). Matsumori et al found that hepatitis C virus infection is often found in cases with dilated cardiomyopathy and that hepatitis C virus have an crucial role in the pathogenesis of cardiomyopathy (Matsumori et al, 1995). It was also suggested that antiviral therapeutics against hepatitis C virus could be indicated in these cases. Other viruses linked with myocarditis include Epstein-Barr virus, cytomegalovirus, herpes simplex virus, influenza A-B and HIV (Magnani & Dec, 2006). Multiple infections with different viruses have also been detected in cases (approximately one quarter of all cases) with systolic left ventricular dysfunction (Kuhl et al, 2005). Influenza A and B may also involve a combined myocarditis risk, particularly in patients with pre-existing cardiovascular diseases (Friman et al, 1995). From the study (Bowles et al, 2003) conducted in 624 patients with myocarditis (116 neonates, 191 infants), it was concluded that most common amplified viral genomes in myocardial tissues

Myocarditis in Childhood: An Update on Etiology, Diagnosis and Management 43

required extracorporeal membrane oxygenation support. From these findings, they assumed that new H1N1 influenza A virus is more frequently associated with a severe form of myocarditis that formerly encountered influenza strains. A study from Spain have also

Numerous bacterial infections may cause myocarditis, involvement of myocardium may have insidious course (electrocardiography changes) or may present with significant signs and symptoms. Fulminant septicaemia may result in myocarditis with fatal course. Most common causes of myocarditis associated with bacteraemia included are meningococcus, streptococcus and Listeria (Brodison&Swann, 1998). Borrelia burgdorferi causes Lyme carditis with acute or chronic course. Recently, a study o 207 children with early disseminated Lyme disease conducted by Costello et al found that 33 children (16%) had mild to fulminant myocarditis, 14 of whom had advanced atrioventricular block (none required permanent pacemaker). Lyme disease may rarely present with cardiomyopathy

Various drugs implicated in the development of myocarditis including; anthracyclins, cyclophosphamide, cisplatin, 5-fluorourasil, Lithium, aminophylline, catecholamines, antibiotics (penicillines, ), phenytoine and trastuzumab (Ellis&Disalvo, 2007). Myocyte injury may occur by direct toxic effect on heart or by provoking hypersensitivity reactions. Hypersensitivity reaction may be indicated fever, sinus tachycardia, peripheral eosinophilia and a rash that follows days to weeks after administration formerly well-accepted agent. Actually, it is not the drugs that heralds the reaction, but its metabolites (haptens) in the cases of hypersensitivity myocarditis. The pathological findings are indistinguishable and are independent of the drug involved. The inflammatory infiltrate predominantly consists of eosinophils, and can be located in focal areas, or diffusely within the myocardium with slight or no sign of necrosis, or substitute fibrosis. If the grade of myocardial inflammation or necrosis is severe, arrhythmias or hemodynamic collapse may likely occur. Eosinophilic necrotising myocarditis is an extreme form of hypersensitivity myocarditis that promptly cause cardiovascular collapse. Eosinophilic myocarditis has been documented following

Systemic diseases that are related with active myocarditis include connective tissue diseases such as systemic lupus erythematosus, mixed connective tissue disease, systemic sclerosis, Churg-Strauss syndrome; celiac disease and Whipple's disease. Protozoal, helmintic and parasitic infections may also present with eosinophilic myocarditis. Myocardial abnormalities in SLE is multifactorial with coronary vasculitis, valvulopathy, hypertension, immune injury and drugs are the major contributors. Myocardial abnormalities are common in autopsy patients. However, clinically apparent myocarditis occurs in < 10 % of cases

Further understanding the etiology of myocarditis will illicit more direct therapeutic approaches such as vaccine and antiviral agents. Although some antiviral agents as ribavirin, oseltamivir and acyclovir have had moderate effect on influenza, RSV pneumonitis and CMV disease, currently there is no specific therapy approved for Enteroviruses, parvovirus B 19 and adenovirus. But, other options may be worth considering. A historical example of a promising therapy for viral myocarditis and prevention of dilated cardiomyopathy is that of decline in the incidence of endocardial fibroelastosis in children after initiation of mumps virus vaccine. It has been known that endocardial fibroelastosis is associated with congestive heart failure and death. Evidence from myocardial samples of patients with EFE supported the hypothesis that it is sequela of

emphasized the importance of myocarditis as a risk factor for mortality.

administration dobutamine and vaccines (Tetanus, small pox).

suggesting that the subclinical form is more frequent (Magnani&Dec, 2006).

(Costello et al, 2009).

included are adenovirus, cytomegalovirus, parvovirus and influenza A (ordered in decreasing frequency). It has been known that HIV may cause myocarditis and dilated cardiomyopathy (Breuckman et al, 2005). Direct viral injury, antiretroviral agents, coinfections and inhibition of contractility through HIV glycoprotein type I 120 play a role in the pathogenesis of myocarditis and dilated cardiomyopathy (Chen et al, 2002). The introduction of highly active antiretroviral therapy (HAART) has significantly reduced the incidence of HIV related- myocarditis. On the other hand, in developing countries where the supply of HAART is limited, researchers have observed increase in prevalence of HIV associated cardiomyopathy (Pugliese et al, 2000).


Table 1. Main etiologies observed in myocarditis.

During the pandemic of influenza A (H1N1), myocarditis was documented in four children (80 children with H1N1 influenza) within a 30-day period (Bratincsak et al, 2010). In their retrospective review, three children had fulminant myocarditis, 1 with fatal outcome and 2

included are adenovirus, cytomegalovirus, parvovirus and influenza A (ordered in decreasing frequency). It has been known that HIV may cause myocarditis and dilated cardiomyopathy (Breuckman et al, 2005). Direct viral injury, antiretroviral agents, coinfections and inhibition of contractility through HIV glycoprotein type I 120 play a role in the pathogenesis of myocarditis and dilated cardiomyopathy (Chen et al, 2002). The introduction of highly active antiretroviral therapy (HAART) has significantly reduced the incidence of HIV related- myocarditis. On the other hand, in developing countries where the supply of HAART is limited, researchers have observed increase in prevalence of HIV

associated cardiomyopathy (Pugliese et al, 2000).

 Parvovirus B19 Influenza A and B Hepatitis C virus Cytomegalovirus

 Corynobacterium diphtheria Rickettsia sp. Hemophilus influenza Vibrio cholerae

 Ascaris sp. Schistosomiasis Echinococcus granulosus Larva migrans Aspergillus sp. Candida Taenia Solium Coccidioides Cryptococcus Histoplasma Toxoplasma gondium Tryponosoma cruzi

 Chagas disease Sarcoidosis Systemic lupus erythamatosus Thyrotoxicosis

Ulcerative colitis Scleroderma

Table 1. Main etiologies observed in myocarditis.

Human herpes virus HIV

Epstein-Barr virus

**Parasitic-Fungal-Protozoal** 

 **Hypersensitivity-Drugs** 

**Immunologic** 

 Coxsackie virus Respiratory syncytial virus Adenovirus Vaccinia (smallpox vaccine)

 Borrelia Burgdorferi Streptoccus pneumoniae Mycobacterial Treponema pallidum Mycoplasma pneumonia Neisseria Meningitides

Rheumatic fever Polymyositis, rheumatic arthritis

Amitriptyline Amphotericin B Arsenic Scorpion envenomation

During the pandemic of influenza A (H1N1), myocarditis was documented in four children (80 children with H1N1 influenza) within a 30-day period (Bratincsak et al, 2010). In their retrospective review, three children had fulminant myocarditis, 1 with fatal outcome and 2

Diabetes Mellitus Wegener's Granulomatosis

 Anthracyclines Electric shock Penicilline Digoxin Phenytoin Copper Dobutamine Colchicine Isoniazide Cephalosporins Iron Lead

**Viral** 

**Bacterial** 

required extracorporeal membrane oxygenation support. From these findings, they assumed that new H1N1 influenza A virus is more frequently associated with a severe form of myocarditis that formerly encountered influenza strains. A study from Spain have also emphasized the importance of myocarditis as a risk factor for mortality.

Numerous bacterial infections may cause myocarditis, involvement of myocardium may have insidious course (electrocardiography changes) or may present with significant signs and symptoms. Fulminant septicaemia may result in myocarditis with fatal course. Most common causes of myocarditis associated with bacteraemia included are meningococcus, streptococcus and Listeria (Brodison&Swann, 1998). Borrelia burgdorferi causes Lyme carditis with acute or chronic course. Recently, a study o 207 children with early disseminated Lyme disease conducted by Costello et al found that 33 children (16%) had mild to fulminant myocarditis, 14 of whom had advanced atrioventricular block (none required permanent pacemaker). Lyme disease may rarely present with cardiomyopathy (Costello et al, 2009).

Various drugs implicated in the development of myocarditis including; anthracyclins, cyclophosphamide, cisplatin, 5-fluorourasil, Lithium, aminophylline, catecholamines, antibiotics (penicillines, ), phenytoine and trastuzumab (Ellis&Disalvo, 2007). Myocyte injury may occur by direct toxic effect on heart or by provoking hypersensitivity reactions. Hypersensitivity reaction may be indicated fever, sinus tachycardia, peripheral eosinophilia and a rash that follows days to weeks after administration formerly well-accepted agent. Actually, it is not the drugs that heralds the reaction, but its metabolites (haptens) in the cases of hypersensitivity myocarditis. The pathological findings are indistinguishable and are independent of the drug involved. The inflammatory infiltrate predominantly consists of eosinophils, and can be located in focal areas, or diffusely within the myocardium with slight or no sign of necrosis, or substitute fibrosis. If the grade of myocardial inflammation or necrosis is severe, arrhythmias or hemodynamic collapse may likely occur. Eosinophilic necrotising myocarditis is an extreme form of hypersensitivity myocarditis that promptly cause cardiovascular collapse. Eosinophilic myocarditis has been documented following administration dobutamine and vaccines (Tetanus, small pox).

Systemic diseases that are related with active myocarditis include connective tissue diseases such as systemic lupus erythematosus, mixed connective tissue disease, systemic sclerosis, Churg-Strauss syndrome; celiac disease and Whipple's disease. Protozoal, helmintic and parasitic infections may also present with eosinophilic myocarditis. Myocardial abnormalities in SLE is multifactorial with coronary vasculitis, valvulopathy, hypertension, immune injury and drugs are the major contributors. Myocardial abnormalities are common in autopsy patients. However, clinically apparent myocarditis occurs in < 10 % of cases suggesting that the subclinical form is more frequent (Magnani&Dec, 2006).

Further understanding the etiology of myocarditis will illicit more direct therapeutic approaches such as vaccine and antiviral agents. Although some antiviral agents as ribavirin, oseltamivir and acyclovir have had moderate effect on influenza, RSV pneumonitis and CMV disease, currently there is no specific therapy approved for Enteroviruses, parvovirus B 19 and adenovirus. But, other options may be worth considering. A historical example of a promising therapy for viral myocarditis and prevention of dilated cardiomyopathy is that of decline in the incidence of endocardial fibroelastosis in children after initiation of mumps virus vaccine. It has been known that endocardial fibroelastosis is associated with congestive heart failure and death. Evidence from myocardial samples of patients with EFE supported the hypothesis that it is sequela of

Myocarditis in Childhood: An Update on Etiology, Diagnosis and Management 45

Fig. 2. Schematic drawings of pathophysiological processes of viral myocarditis. NO: Nitric

First phase terminates with the stimulation of the host immune response that weakens viral proliferation but may also augment viral entry. Under ideal circumstances, immune system should normalize to a resting state once viral proliferation is limited. However, if host immune system stimulation persists unrestricted even with the elimination of the virus, autoimmune disease may develop, activating the second phase. This phase is distinguished by inflammatory cellular infiltration with natural killer cells and macrophages, then consequent expression of proinflammatory cytokines, especially interleukin-1, interleukin-2, TNF and interferon γ (Kawai, 1999, Matsumori et al., 1994). It has been shown that TNF triggers endothelial cells, recruits further inflammatory cells, more enhances cytokine production and has direct negative inotropic effects (Feldman&McNamara, 2000). Cytokines can also induce macrophages to express inducible nitric oxide synthase (NOS) in heart cells (Zaragoza et al., 1998). The role of NO in myocarditis is complicated. NO can reduce viral replication, and peroxynitrate production has strong antiviral effects (Zaragoza et al., 1997). Mice deficient in NOS were found to have greater viral titers and more widespread myocyte injury (Padalko et al., 2004). Alternatively, myosin induced autoimmune myocarditis animal model showed us that NOS expression in myocytes and macrophages is related with more severe inflammation, where NOS inhibitors can have potential to reduce myocarditis severity (Zaragoza et al., 1998, Mikami et al., 1997). Furthermore, improvement in myocarditis of the mouse model has been demonstrated by blocking IL-1b or TNF-a at the onset of the disease (Fairweather et al., 2004). Cihakova et al. also showed that the severity of CVB3 induced myocarditis as well as myosin-induced myocarditis is associated with the levels of IL-1b and IL-18 in the myocardium (Cihakova et al., 2008). T cells are activated in viral myocarditis by classical cell-mediated immunity. Viral peptide fragments are processed in the Golgi apparatus of the myocyte and presented to the cell. These prepared T-cells are capable of identifying the viral antigen and destroy the infected myocyte by

oxide, NK: Natural killer cells.

**3.2 Autoimmunity** 

viral myocarditis, in particular of that due to mumps virus. Based on the chronology of the fading of the disease, Ni et al. suggested that it is likely that vaccination was responsible for the remarkable decrease in documented case of EFE. So it is logical to think that vaccination against parvovirus B19, echovirus and adenovirus could diminish cases of myocarditis and dilated cardiomyopathy.
