Kawasaki disease shock syndrome with extreme leukemoid reaction mimicking hematologic malignancy in an IVIG-resistant child: A case report

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Rationale:Kawasaki disease shock syndrome (KDSS) is a rare but severe complication of Kawasaki disease, often associated with intravenous immunoglobulin resistance, myocardial dysfunction, and higher risk of coronary complications. Leukemoid reaction is extremely uncommon in KDSS and can mimic hematologic malignancy, complicating timely diagnosis and management.Patient concerns:A 4-year-7-month-old boy presented with fever, cervical lymphadenopathy, rash, and hypotension. Laboratory findings showed extreme leukocytosis (peak white blood cell 71.10 × 109/L), initially raising concern for acute leukemia.Diagnoses:The patient was diagnosed with KDSS based on fever, mucocutaneous features, circulatory collapse, multi-organ involvement, and echocardiographic findings. Bone marrow aspiration confirmed reactive hyperplasia without blasts, and additional workup excluded hematologic malignancy.Interventions:The child received intravenous immunoglobulin as first-line therapy but remained resistant. High-dose methylprednisolone was initiated, followed by tapering corticosteroids and low-dose aspirin. Short-term anticoagulation with dipyridamole and low-molecular-weight heparin was introduced as thromboprophylaxis, given the extreme inflammatory burden, hypoalbuminemia, serosal effusions, and elevated coagulation markers. Supportive therapy included albumin infusion, oxygen, and gastric protection.Outcomes:The patient showed rapid resolution of fever and shock after corticosteroid therapy, with progressive normalization of white blood cell and C-reactive protein levels. He was discharged in stable condition. At 1- and 24-month follow-up, laboratory results remained normal, and echocardiography confirmed absence of coronary artery aneurysms or ventricular dysfunction.Lessons:This case emphasizes that KDSS with leukemoid reaction may mimic hematologic malignancy, delaying appropriate immunomodulatory therapy. Extreme leukocytosis (≥70 × 109/L) should not exclude KDSS, especially in children with unexplained fever and shock. Early recognition, adjunctive corticosteroid therapy, and individualized anticoagulation strategies are critical to prevent misdiagnosis and improve outcomes.