Eosinophilic myocarditis

Eosinophilic myocarditis is inflammation in the heart muscle that is caused by the infiltration and destructive activity of a type of white blood cell, the eosinophil. Typically, the disorder is associated with hypereosinophilia, i.e. an eosinophil blood cell count greater than 1,500 per microliter (normal 100 to 400 per microliter). It is distinguished from non-eosinophilic myocarditis, which is heart inflammation caused by other types of white blood cells, i.e. lymphocytes and monocytes, as well as the respective descendants of these cells, NK cells and macrophages. This distinction is important because the eosinophil-based disorder is due to a particular set of underlying diseases and its preferred treatments differ from those for non-eosinophilic myocarditis. Eosinophilic myocarditis is inflammation in the heart muscle that is caused by the infiltration and destructive activity of a type of white blood cell, the eosinophil. Typically, the disorder is associated with hypereosinophilia, i.e. an eosinophil blood cell count greater than 1,500 per microliter (normal 100 to 400 per microliter). It is distinguished from non-eosinophilic myocarditis, which is heart inflammation caused by other types of white blood cells, i.e. lymphocytes and monocytes, as well as the respective descendants of these cells, NK cells and macrophages. This distinction is important because the eosinophil-based disorder is due to a particular set of underlying diseases and its preferred treatments differ from those for non-eosinophilic myocarditis. Eosinophilic myocarditis is often viewed as a disorder that has three progressive stages. The first state of eosinophilic myocarditis involves acute inflammation and cardiac cell necrosis; it is dominated by symptoms characterized as the acute coronary syndrome such as angina, heart attack and/or congestive heart failure. The second stage is a thrombotic stage wherein the endocardium (i.e. interior wall) of the diseased heart forms blood clots which break off, travel in, and block blood through systemic or pulmonary arteries; this stage may dominate the initial presentation in some individuals. The third stage is a fibrotic stage wherein scarring replaces damaged heart muscle tissue to cause a clinical presentation dominated by a poorly contracting heart and cardiac valve disease. Perhaps less commonly, eosinophilic myocarditis, eosinophilic thrombotic myocarditis, and eosinophilic fibrotic myocarditis are viewed as three separate but sequentially linked disorders in a spectrum of disorders termed eosinophilic cardiac diseases. The focus here is on eosinophilic myocarditis as a distinct disorder separate from its thrombotic and fibrotic sequelae. Eosinophilic myocarditis is a rare disorder. It is usually associated with, and considered secondary to, an underlying cause for the pathological behavior of the eosinophils such a toxic reaction to a drug (one of its more common causes in developed nations), the consequence of certain types of parasite and protozoan infections (a more common cause of the disorder in areas with these infestations), or the result of excessively high levels of activated blood eosinophils due to a wide range of other causes. The specific treatment (i.e. treatment other than measures to support the cardiovascular system) of eosinphilic myocarditis differs from the specific treatment of other forms of myocarditis in that it is focused on relieving the underlying reason for the excessively high numbers and hyperactivity of eosinophils as well as on inhibiting the pathological actions of these cells. Symptoms in eosinophilc myocarditis are highly variable. They tend to reflect the many underlying disorders causing eosinophil dysfunction as well as the widely differing progression rates of cardiac damage. Before cardiac symptoms are detected, some 66% of cases have symptoms of a common cold and 33% have symptoms of asthma, rhinitis, urticarial, or other allergic disorder. Cardiac manifestations of eosinophilic myocarditis range from none to life-threatening conditions such as cardiogenic shock or sudden death due to abnormal heart rhythms. More commonly the presenting cardiac symptoms of the disorder are the same as those seen in other forms of heart disease: chest pain, shortness of breath, fatigue, chest palpitations, light headedness, and syncope. In its most extreme form, however, eosinophilic myocarditis can present as acute necrotizing eosinophilic myocarditis, i.e. with symptoms of chaotic and potentially lethal heart failure and heart arrhythmias. This rarest form of the disorder reflects a rapidly progressive and extensive eosinophilic infiltration of the heart that is accompanied by massive myocardial cell necrosis. Hypereosinophilia (i.e. blood eosinophil counts at or above 1,500 per microliter) or, less commonly, eosinophilia (counts above 500 but below 1,500 per microliter) are found in the vast majority of cases of eosinophilic myocarditis and are valuable clues that point to this rather than other types of myocarditis or myocardial injuries. However, elevated blood eosinophil counts may not occur during the early phase of the disorder. Other, less specific laboratory findings implicate a cardiac disorder but not necessarily eosinophilic myocarditis. These include elevations in blood markers for systemic inflammation (e.g. C reactive protein, erythrocyte sedimentation rate), elevations in blood markers for cardiac injury (e.g. creatine kinase, troponins); and abnormal electrocardiograms ( mostly ST segment-T wave abnormalities). Eosinophilic coronary periarteritis is an extremely rare heart disorder caused by extensive eosinophilic infiltration of the adventitia and periadventitia, i.e. the soft tissues, surrounding the coronary arteries. The intima, tunica media, and tunica intima layers of these arteries remain intact and are generally unaffected. Thus, this disorder is characterized by episodes of angina, particularly Prinzmetal's angina, and chaotic heart arrhythmias which may lead to sudden death. The disorder is considered distinct from eosinophilic myocarditis as well as other forms of inflammatory arterial disorders in that it is limited to the coronary artery system. There are many causes of eosinophilia that may underlie eosinophilic myocarditis. These causes are classified as primary (i.e. a defect intrinsic to the eosinophil cell line), secondary (induced by an underlying disorder that stimulates the proliferation and activation of eosinophils), or idiopathic (i.e. unknown cause). Non-idiopathic causes of the disorder are sub-classified into various forms of allergic, autoimmune, infectious, or malignant diseases and hypersensitivity reactions to drugs, vaccines, or transplanted hearts. While virtually any cause for the elevation and activation of blood eosinophils must be considered as a potential cause for eosinophilic myocarditis, the follow list gives the principal types of eosinophilia known or thought to underlie the disorder.