Loeffler endocarditis

Article written and reviewed by Dr Luca Moretti

Loeffler endocarditis is an endomyocardial disease associated with eosinophil-mediated injury, in which inflammation and necrosis may be accompanied by intracavitary thrombosis and subsequent fibrous organization. Involvement mainly affects the ventricular endocardium and adjacent myocardium, with possible extension to the atrioventricular apparatus. The historical term endocarditis does not indicate an infectious cause and does not imply valvular vegetations. Its relationship with eosinophilic myocarditis also requires precision: eosinophilic myocarditis may represent the initial phase of the process, but it may occur without the thrombotic and restrictive phenotype classically described in Loeffler disease.

The condition may develop in the setting of a hypereosinophilic syndrome, a myeloid neoplasm with eosinophilia, an immune-mediated disease, or a reaction to drugs and other exposures. The cardiologic designation therefore does not replace etiologic diagnosis. The same final morphology may result from processes requiring very different treatments, while a patient with eosinophilia may have an unrelated heart disease. Attributing the damage to eosinophils requires integration of clinical course, laboratory findings, imaging, and, when necessary, tissue, while also considering alternative explanations.

The disease is rare and lacks a robust, universally applicable incidence estimate. Eosinophilic myocarditis series, hematologic cohorts, and restrictive cardiomyopathy series describe different populations; moreover, early treatment may prevent development of the chronic lesions that made the condition recognizable in historical descriptions. Prognostic relevance depends on three possibilities: acute deterioration in cardiac function, embolization from mural thrombi, and development of permanent fibrotic restriction. These risks may occur separately or overlap in the same patient.

Etiology, pathogenesis, and pathophysiology

Eosinophils may increase because of clonal proliferation of the myeloid lineage or as a response to stimuli external to the eosinophil compartment. In the first case, molecular abnormalities may activate autonomous proliferative signals; in the second, cytokines such as interleukin 5 support cell production, survival, and activation. Reactive causes include certain parasitic infections, drug reactions, and immune diseases; an aberrant lymphocyte population may in turn produce eosinophilopoietic cytokines. Detection of eosinophilia should therefore open a classification pathway, not conclude it with the generic label of allergy.

Systemic conditions of particular relevance include eosinophilic granulomatosis with polyangiitis and drug hypersensitivity reactions, including DRESS. In the former, cardiac involvement may occur even in the absence of ANCA positivity; in the latter, exposure chronology, rash, and involvement of other organs are essential, but the cardiac manifestation may not coincide temporally with the peak eosinophil count. Myeloid neoplasms with fusions involving PDGFRA or other genes instead require specific hematologic assessment. A diagnosis of idiopathic disease is appropriate only after an adequate investigation and remains subject to reassessment over time.

Damage depends mainly on eosinophil activation and degranulation. Major basic protein, eosinophil cationic protein, and peroxidase products can impair cell membranes, mitochondria, and endothelial integrity. Direct cytotoxicity is accompanied by recruitment of other cells, oxidative stress, and amplification of inflammation. The blood eosinophil count does not quantify these processes: tissue infiltration, degranulation, and cellular redistribution may produce major injury with a peripheral count that is not particularly high, especially after corticosteroid treatment. For the same reason, a rapid fall in the count does not demonstrate immediate resolution of cardiac injury.

In the necrotic-inflammatory component, the infiltrate and cardiomyocyte injury may cause edema, conduction abnormalities, electrical instability, and impaired contractility. Involvement may be focal or extensive and, in fulminant forms, can rapidly compromise both ventricles. Absence of macroscopic endocardial thickening does not exclude this phase. Acute inflammation and microvascular injury may also produce chest pain and electrocardiographic abnormalities resembling ischemia, making it necessary to distinguish an acute coronary syndrome from inflammatory disease and from possible coronary emboli.

Mural thrombosis develops when the injured endocardial surface loses its antithrombotic properties. Eosinophil activation promotes interactions with platelets and coagulation; local stasis and altered kinetics contribute but are not as indispensable as in other settings of ventricular thrombosis. Apical or parietal thrombi may therefore form even without a severe reduction in ejection fraction. Their surface and mobility influence the probability of detachment, whereas extensive adherence to the wall may mask their thrombotic nature and simulate simple endocardial thickening.

Organization of the lesion involves fibroblast proliferation and matrix deposition, with possible incorporation of thrombus. Endomyocardial fibrosis progressively reduces the effective cavity and compliance; incorporation of chordae and papillary muscles causes retraction and mitral or tricuspid regurgitation. The necrotic, thrombotic, and fibrotic phases are therefore a pathogenetic model, not three stages that every patient must pass through in order and within predictable time frames. Mature scar may coexist with residual inflammation and recent thrombus, making a therapeutic choice based on a single temporal category inadequate.

The fibrotic ventricle develops high pressures with modest increases in volume. Restriction limits filling during exercise and makes cardiac output dependent on a narrow balance among preload, heart rate, and atrial function. Ejection fraction may remain apparently normal despite reduced stroke volume, particularly in a partially obliterated cavity. Atrioventricular regurgitation worsens congestion and reduces the proportion of blood effectively directed into the circulation. In right-sided forms, ascites and hepatic congestion may predominate; in left-sided forms, increased pulmonary pressures may shift the load to the right ventricle and produce biventricular deterioration.

Clinical manifestations

Acute onset may include chest pain, dyspnea, palpitations, syncope, and rapid deterioration in exercise tolerance. Fever and fatigue may accompany the systemic process without defining its cause. In severe cases, hypotension, oliguria, altered mental status, and hyperlactatemia indicate impaired perfusion; ventricular arrhythmias or advanced conduction blocks may precede marked cardiac dilatation. The combination of myocardial injury and eosinophilia should prompt timely assessment, but its absence does not justify excluding eosinophilic myocarditis when the other findings are strongly suggestive.

The chronic phenotype is dominated by restrictive heart failure. Dyspnea, orthopnea, and reduced functional capacity are accompanied by jugular venous distention, hepatomegaly, ascites, or edema according to lesion distribution. Major right-sided congestion may develop without severe impairment of left ventricular systolic function; the apparent discrepancy is explained by impaired filling and loss of ventricular volume, not by poor reliability of symptoms. Regurgitant murmurs, irregular rhythm, and signs of hypoperfusion complete the assessment, but absence of an obvious murmur does not exclude major endomyocardial involvement.

Embolic manifestations include focal neurologic deficits, amaurosis, limb ischemia, and abdominal or flank pain due to visceral involvement. Events in different vascular territories may be the first sign of intracardiac thrombosis. With right-sided involvement, sudden dyspnea and chest pain also require investigation for pulmonary embolism. The history should reconstruct events before and after treatment begins, because recurrence during anticoagulation may result from insufficient exposure, persistence of eosinophilic activity, or a different embolic source.

Extracardiac findings help identify the responsible disease. Asthma, rhinosinusitis, polyposis, purpura, and neuropathy suggest a vasculitic context; rash, facial edema, fever, and hepatitis after a new drug suggest a systemic reaction; splenomegaly, cytopenias, or other differential-count abnormalities require hematologic attention. Cutaneous and gastrointestinal symptoms may instead accompany several hypereosinophilic syndromes without distinguishing among them. Travel and residence history should include remote exposures, because some infestations may persist and become particularly dangerous when immunosuppression is started.

It is also useful to reconstruct the treatment chronology: corticosteroids prescribed for asthma or dermatitis may have altered eosinophil counts and biopsy findings; anticoagulants may have reduced thrombus without correcting causal activity; diuretics may lessen congestion while leaving restriction unchanged. Clinical assessment therefore does not concern only the snapshot of the hospitalization. Previous reports, historical blood counts, and changes in functional capacity may reveal a process already present and distinguish a new insult from a stable scarred outcome.

Investigations and diagnosis

Initial tests include ECG, rhythm monitoring in at-risk presentations, troponin, natriuretic peptides, complete blood count with differential and smear, renal and liver function, electrolytes, and inflammatory markers. The eosinophil count should be expressed as an absolute value and interpreted in relation to previous treatments. Troponin indicates myocardial injury but does not identify its cause; a normal value does not exclude chronic fibrosis or thrombosis. Assessment of coronary abnormalities follows clinical probability and presentation, because eosinophilia and coronary disease may coexist.

Echocardiography should look for apical thrombi, endocardial thickening, cavity obliteration, atrial dimensions, function of both ventricles, and mitral or tricuspid involvement. It is important to recognize a truly deformed apex while avoiding foreshortened views; contrast may improve distinction among blood pool, wall, and adherent mass when the border is poorly defined. Thrombus description includes site, extent, mobility, and relationship to the wall, while valve assessment should clarify whether regurgitation results from subvalvular retraction or a different mechanism. A normal initial examination does not exclude early inflammatory injury.

Assessment of filling integrates transmitral and transtricuspid Doppler, annular velocities, estimated pulmonary pressures, and signs of congestion. The meaning of a restrictive pattern depends on rhythm, heart rate, and loading conditions; response to therapy and comparison with previous examinations help distinguish dynamic components from structural limitations. Measurement of forward stroke volume is particularly useful when a preserved ejection fraction appears discordant with low output and symptoms. In cases with major regurgitation, filling parameters should be interpreted while accounting for the volume returning to the atrium.

Cardiac magnetic resonance imaging characterizes the distribution of injury and the composition of intracavitary lesions. Edema and abnormal T1 and T2 parameters support an inflammatory process in the appropriate context; late enhancement may show subendocardial involvement extending beyond coronary territories. Thrombus is generally avascular and may appear as a layer distinct from adjacent fibrosis. Interpretation combines sequences and acquisition times, because an organized thrombus does not necessarily have the same signal as a recent one. The report should also describe how much of cavity loss is due to thrombotic material and how much to organized tissue: regression of the former may restore volume, whereas the latter may maintain restriction. A laminar, minimally mobile thrombus is not equivalent to a protruding or mobile component, and comparisons across examinations should preserve these relationships. Site and distribution are directly documentable findings; eosinophilic attribution remains the result of integration with clinical findings, laboratory data, and, when available, histology.

CMR criteria for myocarditis strengthen the diagnosis of inflammation when concordant T1- and T2-based indicators are present, but they do not replace histologic typing in situations in which histology changes treatment. Absence of edema should also be interpreted according to the timing of the examination and medications already received. A scar with persistent late enhancement may represent residual injury; intensifying immunosuppression solely because enhancement does not disappear risks confusing activity with anatomic consequence. Serial assessment should therefore integrate symptoms, biomarkers, function, and tissue findings.

Endomyocardial biopsy becomes particularly important in fulminant presentations, rapid deterioration, ventricular arrhythmias, or advanced conduction disturbances, when distinguishing eosinophilic myocarditis, giant-cell myocarditis, and other forms changes an urgent decision. Examination may show eosinophilic infiltrate, degranulation, necrosis, and fibrosis, but sampling is limited and a focal distribution may produce false negatives. Imaging and clinical context contribute to selection of the site; thrombi and anatomy alter procedural risk. There is no need to expose every patient with a typical chronic lesion to an invasive procedure when the result would not change management.

At the same time, the cause of eosinophilia is investigated. Drug history, exposure assessment, immunologic evaluation, and hematologic studies are selected according to clinical probability. Identification of FIP1L1::PDGFRA is particularly relevant to treatment choice; the abnormality may be cryptic and not recognized by conventional karyotyping alone. Other fusions and abnormalities require dedicated methods and specialist assessment. Vitamin B12, tryptase, smear morphology, splenomegaly, and abnormalities of other blood cell lines may suggest a myeloid cause, but none of these clues replaces diagnostic demonstration.

Secondary causes should be investigated before applying the idiopathic label. In suspected eosinophilic granulomatosis with polyangiitis, negative ANCA does not exclude the disease and should be interpreted together with the clinical phenotype. Parasitologic testing depends on exposure and the suspected organism; a single negative stool examination does not resolve every possibility. Evaluation for Strongyloides is particularly important before corticosteroids in exposed individuals, using a strategy that accounts for cardiac urgency. If the systemic diagnosis remains uncertain, it is more appropriate to describe the degree of probability of eosinophilic attribution than to convert a temporal association into definitive proof.

The differential diagnosis includes post-infarction apical thrombosis, dilated cardiomyopathies with stasis, apical hypertrophy, endomyocardial fibrosis in endemic areas, and other myocarditides. Scar distribution and coronary history help distinguish ischemia from eosinophilic injury; a valvular mass with fever or bacteremia instead requires investigation for infective endocarditis. There is no universal set of echocardiographic findings alone that certifies Loeffler disease. The diagnostic conclusion should state the cardiac phenotype, presumed activity, documented or suspected cause, and presence of thrombosis, because these are the elements that guide treatment.

Treatment and prognosis

In acute disease with hemodynamic compromise, the first objective is to stop injury and support the circulation. Intensive monitoring, arrhythmia treatment, and management of shock may require a center capable of performing biopsy and mechanical circulatory support. Useful diagnostic samples should be obtained rapidly, but completion of the entire etiologic work-up must not delay lifesaving treatment. Temporary support is meaningful as a bridge to response to causal therapy or to a subsequent decision, because part of the inflammatory dysfunction may be reversible.

Glucocorticoids are a central treatment in many forms of active eosinophilic injury, with intensity proportionate to severity and subsequent tapering guided by response. They are not, however, a universal etiologic solution: the responsible drug should be withdrawn in hypersensitivity reactions, a relevant infectious cause should be treated, and the specific regimen should be instituted in vasculitides. In patients with possible Strongyloides exposure, prevention or treatment of hyperinfection should be coordinated with urgent initiation of immunosuppression. Response is assessed in the heart and other organs, not only by the eosinophil count.

When a sensitive fusion is documented, imatinib may control the clonal process with efficacy very different from that of nonspecific therapy. Choice and monitoring belong within hematologic management and account for the molecular target; not all neoplasms with eosinophilia share the same sensitivity. In patients with cardiac involvement, treatment initiation requires close surveillance and may be accompanied by corticosteroids according to specialist context. A rapid hematologic response does not eliminate the need to follow thrombi, valves, and filling, which may improve more slowly or remain impaired.

In appropriate hypereosinophilic syndromes, mepolizumab may reduce relapses and the need for corticosteroids as part of a systemic control strategy. Evidence obtained in selected patients with chronic disease does not demonstrate that the drug replaces urgent treatment of fulminant myocarditis, nor that it reverses a mature endocardial scar. Other immunomodulatory or cytoreductive therapies are chosen according to subtype, response, and toxicity. The decision should therefore start from causal diagnosis, avoiding the same regimen for every patient with the cardiac phenotype of Loeffler disease.

A documented intracardiac thrombus requires assessment for therapeutic anticoagulation, integrated with control of eosinophilic activity. Site, mobility, previous emboli, renal function, bleeding risk, and planned procedures guide the drug and initial strategy. In an unstable patient or one approaching a procedure, the ability to adjust and rapidly interrupt the effect may initially favor unfractionated heparin; during longer-term treatment, reliable monitoring and other indications, such as a mechanical prosthesis, are also considered. Comparative evidence specific to this disease is limited: favorable experience with an anticoagulant in other forms of ventricular thrombosis does not demonstrate equal efficacy in an endocardium still exposed to eosinophilic injury.
Duration is reassessed according to thrombus resolution, persistence of the abnormal surface, and activity of the cause; normalization of the blood count alone is not a sufficient criterion for stopping protection.

Management of heart failure depends on phenotype. In systolic dysfunction, appropriate and tolerated treatments are considered, whereas in fibrotic restriction decongestion requires particular attention to preload reduction. Blood pressure, perfusion, renal function, and electrolytes help distinguish useful diuresis from excessive volume removal. Heart-rate and rhythm control should preserve filling without depressing an already limited output; new conduction disturbances or ventricular arrhythmias also require reassessment of myocardial activity and the need for specific protection.

Endomyocardial surgery is discussed when cavity obliteration and severe regurgitation cause major symptoms despite adequate medical management. Endocardiectomy and valve repair or replacement should be planned together, considering the extent of fibrosis, amount of residual myocardium, biventricular involvement, and organ damage. Operating on a still-active substrate may leave a risk of recurrence and thrombosis; on the other hand, waiting for pharmacologic regression of an already fixed deformity may forfeit a chance for correction. In terminal cases, transplantation also requires assessment of the controllability of the systemic disease.

Follow-up distinguishes biologic remission from cardiac recovery. Eosinophil counts and molecular markers track the systemic process; troponin and imaging contribute to cardiac assessment; symptoms, stroke volume, regurgitation, and congestion describe the functional result. A persistent scar may remain clinically relevant despite control of the cause. Conversely, deterioration after a period of stability may result from inflammatory relapse, new thrombus, arrhythmia, or mechanical progression, with different therapeutic implications. Prognosis is better when the process is recognized before organized thrombosis and fibrosis have irreversibly altered anatomy.

Complications

Systemic emboli may cause stroke, mesenteric ischemia, renal or splenic infarction, and acute limb ischemia. Severity depends on territory, duration of occlusion, and possibility of reperfusion, not only on the size of residual thrombus seen in the heart. After stroke, infarct extent and hemorrhagic component influence the timing of anticoagulation and cardiac procedures. Assessment should also distinguish embolism from local thrombosis, because eosinophilic syndromes may alter coagulation outside the cardiac chambers.

Progression to irreversible restriction causes persistent congestion and reduced output reserve. Mitral or tricuspid regurgitation, pulmonary hypertension, and dysfunction of the opposite ventricle may create a cycle of hemodynamic deterioration, compounded by renal failure, congestive hepatopathy, and malnutrition. These outcomes are not necessarily evidence of persistent eosinophilic activity: they may result from established damage and require a mechanical or advanced-support strategy rather than simply intensified immunosuppression.

Ventricular arrhythmias and conduction blocks may complicate acute injury; over the long term, scar may maintain an arrhythmogenic substrate even after inflammation is controlled. Atrial fibrillation adds loss of atrial contribution, possible hemodynamic instability, and thromboembolic risk. Risk assessment should be updated after the acute phase, because functional recovery and persistence of electrical events do not necessarily follow the same course.

Treatment carries risks of bleeding, infection, metabolic toxicity, and drug-specific adverse effects. A relapse during corticosteroid tapering should be distinguished from intercurrent infection and decompensation on scar; similarly, bleeding does not automatically eliminate the need for embolic prevention but requires reassessment of the clinical balance. After surgery, thrombogenicity, valve dysfunction, or residual restriction may persist. Continuity among cardiology, hematology, and the specialty responsible for the cause is therefore part of complication management, particularly during transitions from hospitalization to causal treatment and long-term surveillance.