Background Kawasaki disease (KD) is a systemic vasculitis that occurs predominantly in young children. Diagnosis is based on clinical criteria of KD. Coronary artery lesions are the most important complications of KD. First-line treatment consists of intravenous immunoglobulin (IVIM) administration. There are biological markers that are considered predictors of treatment response and heart complications.

Aims highlighting factors that influence treatment response and heart complications in KD.

Methods We had to investigate a paediatric patient with persistent fever. A 3 years old boy presented with a history of fever over 10 days, sore throat, and pain and swelling of the knee. The boy diagnosed with acute tonsillitis received intravenous antibiotics treatment with Ceftriaxone and Gentamicin and medications for fever in paediatric service in Hunedoara without effect. After starting antibiotic treatment the patient had an erythematous rash on the trunk.

Results In our service the physical examination revealed fever, hyperemia of both eyes, cervical and inguinal lymphadenopathy, throat congestion, red lips, strawberry tongue, swelling of knees and hands and feet fingers, and exanthema of palms and soles with scaling. Laboratory investigations revealed a biological inflammatory syndrome with elevated erythrocyte sedimentation rate, high level of C-reactive protein and fibrinogen, leukocytosis, important thrombocytosis(>1mil/mm³), normochromic microcytic anaemia, and elevated alanine aminotransferase. Immunological investigations were negative. Serological investigations revealed a positive value of Cytomegalovirus IgM antibody. Clinical features presented by the patient meet the diagnostic criteria of KD in the second phase of evolution. We decided administration of IVIM with a dose of 2 g/kg over 10 hours. Fever resolves but echocardiography reveals a right coronary artery aneurysm. The patient receives Aspirin in anti-inflammatory high dose (100 mg/kg/day) for 10 days, after which it is recommended maintenance dose. Echocardiographic reevaluations indicate progressive remission of the aneurysm.

Conclusions Particularities of the case: thrombocytosis>1 mil/mm³, criteria that is not listed among predictors of treatment response, but in our experience we had a case with important thrombocytosis in KD with unfavourable outcome; delayed administration of IVIM due to the difficulty of diagnosis; occurrence of coronary aneurysm in subacute phase.