Loffler endocarditis as an initial manifestation of lung adenocarcinoma: A case report.

RATIONALE: Löffler endocarditis, a rare form of hypereosinophilic syndrome (HES), is characterized by transient left ventricular endomyocardial thickening, intracardiac thrombi, and eosinophilic infiltration. Its occurrence as a paraneoplastic manifestation of solid tumors, particularly lung adenocarcinoma, is exceedingly rare and underrecognized. PATIENT CONCERNS: A 75-year-old male smoker presented with progressive dyspnea (New York Heart Association Class III) and bilateral leg edema. DIAGNOSES: He had no history of asthma, allergy, or parasitic infection. Physical examination revealed jugular venous distention and bilateral crackles. Laboratory tests showed marked hypereosinophilia (15.29 × 109/L). Transthoracic echocardiography demonstrated endomyocardial thickening, reduced left ventricular compliance, and mobile intracardiac thrombi. Computed tomography angiography revealed a spiculated left upper lobe lung mass with mediastinal lymphadenopathy. INTERVENTIONS: Symptoms developed over 4 weeks. Hypereosinophilia and cardiac abnormalities were identified at presentation. The lung mass was detected on initial imaging; histopathology confirmed adenocarcinoma (biopsy-proven). Despite anticoagulation and heart failure therapy, the patient declined corticosteroids and oncologic treatment. Clinical deterioration occurred within 2 weeks, leading to death. The patient received guideline-directed medical therapy for heart failure (beta-blocker, angiotensin-converting enzyme inhibitor, diuretics), anticoagulation (low-molecular-weight heparin), and diagnostic bronchoscopic biopsy. Corticosteroids and chemotherapy were recommended but refused by the family. OUTCOMES: The patient's condition rapidly worsened due to progressive heart failure and untreated malignancy. LESSONS: This case highlights the importance of considering occult malignancy in unexplained HES with cardiac involvement. It is the first reported case of Löffler endocarditis as a paraneoplastic manifestation of lung adenocarcinoma. Limitations include the lack of postmortem examination and the inability to initiate immunosuppressive or antitumor therapy due to patient refusal.