[Clinical analysis of 15 cases of severe <i>Mycoplasma pneumoniae</i> pneumonia complicated by cardiac thrombosis in children].

<b>Objective:</b> To investigate the clinical manifestations, therapeutic strategies and prognostic outcomes in pediatric patients with severe <i>Mycoplasma pneumoniae</i> pneumonia (SMPP) complicated by cardiac thrombosis. <b>Methods:</b> This case series study retrospectively analyzed 15 pediatric patients with SMPP complicated by cardiac thrombosis. The patients was recruited from the Department of Pediatric Respiratory Medicine at Shandong Provincial Hospital Affiliated to Shandong First Medical University between July 2018 and January 2025. Comprehensive clinical data and follow-up information were collected. <b>Results:</b> Among the 15 children, 10 were male and 5 were female, and the age of onset was 8.0 (6.3, 10.0) years. All 15 children presented with fever and cough, while additional symptoms included dyspnea in 7 cases, chest pain in 6 cases, hemoptysis in 3 cases, and chest tightness in 1 case. The white blood cell count was 11.7 (9.5, 15.9)×10⁹/L, C-reactive protein was 31.6 (17.5, 64.8) mg/L and lactate dehydrogenase was 548.2 (410.4, 768.3) U/L. A total of 14 children underwent testing for the <i>Mycoplasma pneumoniae</i> drug resistance genes 2063A>G and 2064A>G, of which 13 tested positive. The plasma D-dimer levels of 15 children were 8.77 (7.23, 12.50) mg/L, all of which were higher than normal. Among the 15 children, 5 had decreased activity of anticoagulant proteins (protein C, protein S, antithrombin Ⅲ), and 8 tested positive for antiphospholipid antibodies. Chest CT scans of all 15 children showed pulmonary consolidation and (or) atelectasis, with pleural effusion present in 12 cases. In the 15 children, thrombosis was detected at 14.0 (11.0, 18.0) days after the onset of illness. The locations of cardiac thrombosis included the right ventricle in 9 cases, the right atrium in 5 cases, and the left atrium in 1 case. Additionally, 10 cases had pulmonary vascular embolism, comprising 9 cases of pulmonary artery thrombosis and 1 case of pulmonary vein thrombosis. After anticoagulant treatment, cardiac thrombi disappeared in 10 children. Five children who did not show improvement with anticoagulation underwent surgical thrombectomy. In the follow-up of 15 children, lung imaging basically returned to normal, with no major hemorrhagic events or other adverse events. <b>Conclusions:</b> In children with <i>Mycoplasma pneumoniae</i> pneumonia, the presence of clinical symptoms such as shortness of breath, chest pain and hemoptysis, along with elevated plasma D-dimer levels, should raise suspicion for the possibility of cardiac thrombosis. SMPP complicated by cardiac thrombosis, prognosis is good following anticoagulation or surgical treatment.