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This article is open access.Mevalonate kinase deficiency (MKD) is a rare autosomal recessive disorder causing 1 of 2 phenotypes, hyperimmunoglobulin D syndrome and mevalonic aciduria, presenting with recurrent fever episodes, often starting in infancy, and sometimes evoked by stress or vaccinations. This autoinflammatory disease is caused by mutations encoding the mevalonate kinase (MVK) gene and is classified in the group of periodic fever syndromes. There is often a considerable delay in the diagnosis among pediatric patients with recurrent episodes of fever. We present a case of an 8-week-old girl with fever of unknown origin and a marked systemic inflammatory response. After excluding infections, a tentative diagnosis of incomplete Kawasaki syndrome was made, based on the finding of dilated coronary arteries on cardiac ultrasound and fever, and she was treated accordingly. However, the episodes of fever recurred, and alternative diagnoses were considered, which eventually led to the finding of increased excretion of mevalonic acid in urine. The diagnosis of MKD was confirmed by mutation analysis of the MVK gene. This case shows that the initial presentation of MKD can be indistinguishable from incomplete Kawasaki syndrome. When fever recurs in Kawasaki syndrome, other (auto-)inflammatory diseases must be ruled out to avoid inappropriate diagnostic procedures, ineffective interventions, and treatment delay
