Loeffler endocarditis is restrictive cardiomyopathy, defined as an impaired relaxation of the heart with impaired diastolic filling. Diffuse eosinophil infiltration of the heart causes it First described by the W Loeffler in 1936. The condition is associated with peripheral eosinophilia which lasts for 6 months. It is one of the rare complications of Hyper-eosinophilic syndrome, which is the eosinophilic infiltration of the tissues with no obvious etiology.  Eosinophilic endomyocardial disease or fibroblastic endocarditis can be used interchangeably for Loeffler endocarditis. The patient may present with an intracardiac thrombus, arrhythmias, and/or acute heart failure which can be life-threatening, if not treated early.
As mentioned earlier Loeffler endocarditis is a rare manifestation of hypereosinophilic syndrome (HES) which is divided into idiopathic, primary, and secondary types based on the underlying etiology. Idiopathic hypereosinophilic syndrome is a rare entity with no obvious cause of elevated eosinophil count and is the most common cause of Loeffler endocarditis. The primary type has been associated with an underlying myeloproliferative and stem cell disorders like leukemia and lymphoma. Secondary hypereosinophilic syndrome is reactive to an underlying non-neoplastic or paraneoplastic condition causing expansion of non-clonal eosinophils like allergic conditions, parasitic, fungal infections, and tumors.
Hypereosinophilic syndrome is a very rare disorder with an annual incidence of 0.036 per 100,000 patients. The disease is rare in North America and mostly includes temperate and tropical areas of Asia, Africa, and some areas of South America. This condition is usually diagnosed between the ages of 20 to 50 years of age but may present at extremes of age. Cardiac involvement is present in 50% of the cases. It has no gender predisposition, except for primary hypereosinophilic syndrome, which is more common in men than women.
The pathophysiology of HES is not well understood. Some experts suggest that if the eosinophil count remains elevated (greater than 1500 eosinophils 10/L of peripheral blood) over 5 months, the incidence of end-organ damage increases which may involve the heart, lungs, central nervous system, lungs, spleen, and the gastrointestinal (GI) tract. When eosinophils infiltrate the heart, they secrete protein granules which damage the endocardium and myocardium by producing direct toxins which, in turn, activate platelets. The activated platelets later combine to form intracavitary and intravascular thrombi which can lead to further damage of the endocardium. Few other mechanisms include activation of VWF and factor XII which may disrupt endothelial lining that enhances procoagulant activity and activate fibrin production.
A biopsy is the mainstay of diagnosis but requires an invasive intervention. Light microscopy shows degranulated eosinophils and eosinophil cationic protein in the endocardium and activated eosinophils at the myocardial interstitium. On electron microscopy, a characteristic cardiac myocytolysis change showing disruption at the intercellular junctions is observed. The endocardium of one or both ventricles is typically fibrosed and thickened, affecting the underlying myocardium. Large mural thrombi may develop in either the right or left ventricle, resulting in a reduction in ventricular cavity size, being a potential source of pulmonary and systemic emboli. Histological features also comprise inflammation of the small intramural coronary vessels.
Patients with Loeffler endocarditis may present with signs and symptoms of acute heart failure. Dyspnea, palpitation, chest pain, cough, fatigue, shortness of breath, and unintentional weight loss are the common presentations. Sixty percent of cases present with the chief complaint of shortness of breath. Rare cases present with symptoms and signs of pericarditis (4%). Thirty-eight percent may develop congestive heart failure. Eosinophilic infiltration may cause valvular abnormality and most commonly involve the mitral valve, causing mitral valve insufficiency (42%). It can also involve the aortic wall leading to aortic stenosis and regurgitation, which is present in 4% of the cases.
The following investigational studies can be done to diagnose endocarditis due to eosinophilic infiltration:
Symptomatic management of Loeffler endocarditis can be achieved with supportive care with diuretics, digoxin, and conventional therapy for heart failure including angiotensin-converting enzyme (ACE) inhibitor, angiotensin II receptor blockers, beta-adrenergic blockers, and aldosterone antagonists.
Patients with Loeffler endocarditis typically need mitral valve replacement due to mitral regurgitation. The mitral valve can be replaced with either a mechanical or bioprosthetic valve, but due to a high incidence of mechanical valve thrombosis, a biological valve is preferable. There is no indication for prophylactic anticoagulation in Loeffler endocarditis. If a ventricular thrombus is diagnosed via echocardiography or CMR, anticoagulation should be started. Warfarin or low molecular weight heparin can be used in patients with Loeffler endocarditis with ventricular thrombus or when a mechanical mitral valve is implanted.
Treatment of the underlying HES should be started as soon as the diagnosis is made. Steroids are the first-line therapy for HES due to its anti-inflammatory effect. Hydroxyurea can be used as a second-line agent depending on the etiology of the condition. All patients diagnosed with HES with or without cardiac involvement should have genetic testing for FIP1L1-PDGFRA mutation as it affects the management of the disease. Those who are positive for mutation should be treated with imatinib, a tyrosine kinase inhibitor, which has shown to provide a good treatment response in the literature.
There are 3 pathological stages of Loeffler endocarditis.
Regarding prognosis, patients are divided into 2 groups: steroid responders and non-steroids responders.
Steroid responder patients have a good prognosis, and non-steroid responders have a poor prognosis.
Patients with Loeffler syndrome due to genetic mutation also have a good prognosis after treatment with tyrosine kinase inhibitors.
Due to its rarity, clear-cut mortality has not been defined.
Complications include the following:
Loeffler syndrome is a rare disorder and its presentation may be vague. It is important to keep the diagnosis in mind, because without prompt treatment, the disorder is progressive with a poor outcome. A multidisciplinary team that includes a cardiologist, cardiac surgeon, rheumatologist, internist and cardiac care nurses is ideal for the management of these patients. After valve replacement, the cardiac surgery nurse is responsible for monitoring the patient until discharge.
It's important to diagnose it earlier and closely follow up the patient even though they are asymptomatic. Based on isolated case reports, the outcomes of most patients with Loeffler syndrome is good to excellent.
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