A 3-month old male child was admitted to the Emergency Department of Shaanxi Provincial People' s Hospital for a 2-h history of low-grade fever (peak 37.7 °C) and maculo-papular rash. At admission there were no other symptoms or relevant clinical signs and no history of previous treatments. At physical examination the child was febrile, with mild tachycardia (145/min), normal breathing rate (36/min) and blood pressure (68/55 mmHg). A maculo-papular slightly prominent rash was evident on the trunk and limbs. Lymph nodes were not enlarged, there were no signs of conjunctivitis or mucositis. Neurological, abdominal, and cardiovascular examinations were all normal. Pulmonary auscultation revealed presence of coarse crepitations. Weight was 6.2 kg and length was 64.7 cm (both appropriate for age). Routine blood test showed relative neutrophilia (75%, mean value for age: 32%), with normal white blood cells count (12.73 × 109/L), hemoglobin level (133 g/L) and platelet count (199 × 109/L), increased high-sensitivity C-reactive protein (> 5 mg/L) and C-reactive protein (23.1 mg/dL). A naso-pharyngeal swab for Coronavirus-19 tested negative. The child was admitted and an empiric treatment with IV cefotaxin was started. On the 2nd day of admission, the child was still febrile (39.5 °C) with increased irritability, abdominal distension and cold extremities and rash spread to the face and trunk. Swelling and redness of the hands and feet, lips and oral mucosa redness (strawberry tongue), bilateral conjunctivitis and perioral redness became evident, as shown in Fig. a-e. Repeated blood tests revealed raised pro-calcitonin (7.676 ng/mL), slightly increased liver enzymes (ALT 89 U/L, AST 44 U/L) and mild hypoalbuminemia (30.6 g/L). Leukocyturia (white blood cells 3 +) and proteinuria (582.6 ul) were evident at urine analysis. The main infective causes were excluded, including TORCH, EBV, gastrointestinal infection (normal stool culture and viral investigations), upper respiratory tract infection (negative pharyngeal swab). COVID serology was negative, such as blood and urine cultures. Mild signs of pulmonary inflammation were found on chest X-ray. Antibiotic treatment was switched to ceftriaxone to increase the spectrum and glycyrrhizin was introduced for liver protection. Three days after admission, blood analyses showed increased leukocytosis and clotting derangement (Fibrinogen: 6.08 g/L, Fibrin degradation products: 25.6 mg/L, D-dimer 9.62 mg/L). An echocardiogram showed normal diameter of the left main coronary artery (1.9 mm, z-score: 1.17, LCA/AO = 0.21), left anterior descending branch dilatation (1.8 mm, z-score: 2.08, LAD/AO = 0.20), and presence of a coronary aneurysm at the proximal right coronary artery (3.6 mm, z-score: 6.98, RCA/AO = 0.40) [], with intra-aneurysmatic non-occlusive thrombosis. Despite the young age and the short history of symptoms, a diagnosis of KD was considered. After obtaining parental informed consent, treatment with intravenous human immunoglobulin (IVIG, 2 g/Kg) was immediately given to block the immune response process and reduce further coronary damage. At the same time, a combination of anticoagulant therapies including oral aspirin (100 mg bid) and dipyridamole (12.5 mg bid) was prescribed. Despite a transient relief of symptoms for one day, 24 h after IVIG administration, fever, rash and the other clinical manifestations and biochemical signs recurred. A second dose of IVIG (2 g/Kg) was infused, along with intravenous steroids (methylprednisolone, 2 mg/kg). Following this treatment, symptoms rapidly disappeared, with an increase in platelet count to (770 × 109/L) and evidence of hands and feet desquamation. A second echocardiography repeated after one week showed stable findings. The patient was clinically stable and therefore discharged from hospital on day 14 after a 3rd echocardiography showing a mild improvement (LCA z-score: 0.86, LAD z-score: 0.43, RCA z-score: 6.01) and a regular follow-up was conducted after discharge according to the management plan (formulated by the Kawasaki Disease Cooperation Group of the Pediatric Branch of the Chinese Medical Association and the relevant guidelines of Japan and the United States) [,, ]. Two weeks post-discharge, the echocardiography showed no significant improvement in the coronary artery lesion and the thrombosis measures. Liver enzymes were significantly increased (ALT 119 U/L, AST 54 U/L). Therefore, warfarin treatment (0.09 mg/kg) was introduced, maintaining prothrombin international normalized ratio (INR) between 2 and 3 and aspirin and dypiridamole were stopped. Liver enzymes normalized after one week. At 4 weeks from discharge (day 46) the child was clinically well, weight was 6.7 kg and length was 66 cm. The echocardiography did not show evidence of thrombosis and dilatation of coronary artery was markedly improved ((LCA 1.6 mm, z-score: 0.12, LAD: 1.8 mm, z-score: 1.95, RCA 1.6 mm, z-score: 0.79). The results of echocardiography on the 46th day of disease are shown in Fig.. At final follow-up (7 weeks post-discharge), the echocardiogram showed LCA 2.0 mm, z-score 1.47and RCA 1.6 mm,z-score: 0.79. Platelet count progressively normalized during observation and other blood tests were repeatedly normal.