Mitral endocarditis: successful repair following splenic and cerebral emboli

Differential diagnosis of infective endocarditis: a clinical challenge in the healthy adolescent

Infective endocarditis (IE) is a rare pathology within the pediatric population, particularly in individuals without a history of congenital heart disease. However, the incidence of native valve cases in young subjects without identified risk factors is increasing. These situations pose a complex diagnostic challenge, as initial symptoms can mimic endemic infectious pathologies, thereby delaying vital management.

This study presents the clinical case of a 16-year-old adolescent in Rio de Janeiro, initially misdiagnosed with dengue fever due to a clinical presentation combining fever, myalgia, thrombocytopenia (44,000/mm³), and purpura. The objective is to detail the fulminant progression of methicillin-susceptible Staphylococcus aureus (MSSA) IE and to highlight the importance of differential diagnosis when faced with a petechial rash.

Through this case, the authors document the management of severe systemic embolic complications — affecting the spleen, kidneys, central nervous system, and lower limbs — and evaluate the efficacy of a therapeutic strategy combining targeted antibiotic therapy, splenectomy, and early mitral valve repair surgery. This case report illustrates the need for systematic screening for embolic phenomena to optimize the prognosis in this context of high bacterial virulence.

Management methodology

This clinical case report documents the diagnostic and therapeutic strategy applied to a 16-year-old patient with no cardiovascular history, initially suspected of having dengue fever. The definitive diagnosis of infective endocarditis (IE) on a native valve was established according to the modified Duke criteria, correlating clinical, microbiological, and imaging data.

• Microbiological and biological evaluation: The protocol included the collection of three sets of blood cultures, C-reactive protein (CRP) analysis, and rapid testing for HIV, hepatitis (HBV, HCV), and syphilis. The identified strain was a methicillin-sensitive Staphylococcus aureus (MSSA).
• Imaging and embolic screening: Morphological evaluation was based on transthoracic echocardiography (TTE) with 3D reconstruction, transesophageal echocardiography (TEE) at D4, as well as thoraco-abdominal and lower limb computed tomography (CT) scans. A brain MRA completed the preoperative assessment to look for ischemic foci.
• Therapeutic regimen: Antibiotic therapy consisted of an empirical phase (vancomycin and ceftriaxone), followed by targeted treatment with oxacillin (2g every 4h). Due to persistent sepsis and embolic phenomena, rifampicin (300mg every 8h) was introduced on the 19th day.
• Surgical interventions: The patient underwent a splenectomy on D13 for a major splenic abscess (10.8 cm), followed on D22 by a mitral valve repair with insertion of an annuloplasty ring.
• Histopathological analyses: Valvular and splenic specimens were analyzed using Gram and Grocott-Gomori staining to characterize vegetations and foci of suppuration.

Clinical and surgical management results

The initial biological assessment revealed thrombocytopenia at 44,000/mm³ (evolving to 66,000/mm³ on admission), associated with a C-reactive protein (CRP) of 18 mg/dl (normal < 0.5 mg/dl). Blood cultures revealed, in less than 24 hours, the presence of Gram-positive cocci identified as methicillin-sensitive Staphylococcus aureus (MSSA).

Imaging examination	Key observations
Echocardiography (TTE/TOE)	19 x 10 mm vegetation on the posterior leaflet of the mitral valve.
Abdominal Scan	Splenic abscess (10.8 x 10.5 x 7.1 cm) and collection in the left renal cortex (5.5 x 4.3 x 3.1 cm).
CT angiography (Lower limb)	Obstruction of the tibioperoneal trunk over 2.3 cm and of the proximal anterior tibial artery over 0.7 cm.
Cerebral MR Angiography	Right frontal lacunar infarct and left parietal subarachnoid hemorrhage.

The clinical evolution was marked by persistent fever and the appearance of multiple embolic phenomena despite appropriate antibiotic therapy. Histopathological analysis of the splenectomy specimen confirmed the presence of Staphylococcus aureus within the purulent collections.

Sur le plan chirurgical, le patient a bénéficié d'une splénectomie au 13ème jour d'hospitalisation, suivie d'une réparation de la valve mitrale avec insertion d'un anneau au 22ème jour. Le patient a été autorisé à quitter l'établissement au 54ème jour sous cotrimoxazole et rivaroxaban, après une stabilisation clinique complète.

The limitations of this study lie in its unique nature (n=1), preventing statistical generalization. However, it confirms literature data on the increasing incidence of S. aureus IE in healthy pediatric patients. It reiterates the imperative for systematic screening of embolic phenomena by imaging (CT/MRI) as soon as the Duke diagnosis is confirmed, even in the absence of initial focal signs.

Summary of clinical results

This case of S. aureus (MSSA) infective endocarditis (IE) in a 16-year-old adolescent, initially mistaken for dengue fever due to thrombocytopenia and petechiae, highlights the virulence of native valve involvement. Despite the absence of underlying heart disease, the patient developed multiple emboli (10.8 cm splenic abscess, cerebral infarctions, lower limb ischemia) originating from a 19 x 10 mm mitral vegetation, requiring a splenectomy on day 13 and mitral valve repair on day 22.

In concrete terms, for the practitioner:

• Differential diagnosis alert: Faced with fever associated with a purpuric rash and thrombocytopenia, do not limit yourself to diagnoses of dengue or meningococcal disease; systematic cardiac auscultation is essential to detect a mitral murmur unmasking IE.
• Systematic extension work-up: The identification of S. aureus requires an active search for embolic phenomena via thoraco-abdominal CT scan and brain MRI, even in the absence of focal signs, as vegetation size is a major predictor of migration.
• Early surgical strategy: In the event of persistent infectious syndrome or recurrent emboli despite appropriate antibiotic therapy (here oxacillin then cefazolin), valve repair surgery with a ring should be preferred over replacement to preserve the valve capital of the young patient.

In Rio de Janeiro, a 16-year-old adolescent with no medical history or identified risk factors recently illustrated the danger of a misdiagnosis within a viral endemic context. Initially treated for suspected dengue fever, this patient actually presented with devastating *Staphylococcus aureus* infectious endocarditis (IE), complicated by a cascade of multi-organ embolisms. This case highlights the imperative for diagnostic rigor when faced with fever associated with purpuric skin signs.

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