Atypical mitral valve infective endocarditis presenting with fever and left upper abdominal pain due to splenic infarction: a case report.

Infective endocarditis (IE) may present with non-specific systemic symptoms and embolic complications, making early diagnosis challenging, particularly when initial transthoracic echocardiography (TTE) is non-diagnostic. We report a case of atypical mitral valve IE in a 40-year-old man who presented with persistent fever and left upper abdominal pain rather than overt cardiac symptoms. On admission, inflammatory markers were elevated, whereas emergency chest and abdominal computed tomography showed no definite acute infectious focus. Initial TTE demonstrated only mild mitral and tricuspid regurgitation, with no definite vegetation. However, bedside cardiac auscultation identified a grade 3-4/6 systolic murmur at the mitral area, prompting further investigation. Contrast-enhanced abdominal magnetic resonance imaging subsequently revealed splenic infarction, indicating an embolic event. Blood cultures from both aerobic and anaerobic bottles grew Streptococcus sanguinis. In the setting of persistent fever, positive blood cultures, a prominent systolic murmur, and splenic embolic involvement, transesophageal echocardiography (TEE) was performed and demonstrated a 7 × 5 mm echogenic lesion on the atrial side of the mitral valve, together with moderate mitral regurgitation, supporting the diagnosis of IE. Following targeted intravenous antimicrobial therapy, the patient became afebrile, abdominal pain resolved, and inflammatory markers progressively normalized. Follow-up TEE showed persistent moderate mitral regurgitation without the previously observed abnormal echogenic lesion, and the patient was discharged in improved condition with oral antibiotics and arranged cardiology follow-up. Infective endocarditis should remain in the differential diagnosis of patients with fever of unclear origin accompanied by abdominal pain or splenic infarction, particularly when initial transthoracic echocardiography is non-diagnostic. In such settings, careful physical examination, timely blood culture acquisition, and early transesophageal echocardiography may help avoid diagnostic delay.