Characteristics of Kawasaki disease in infants younger than six months of age

Background: Kawasaki disease is the leading cause of acquired heart disease in childhood. However, there are only a few reports in infants younger than 6 months. The objective of this study is to investigate the clinical and laboratory characteristics of Kawasaki disease in infants younger than 6 months. Methods: From 1994 to 2003, 120 patients with Kawasaki disease diagnosed at our institution were included. Group 1 consisted of 20 (17%) patients younger than 6 months, and group 2 consisted of 100 (83%) patients older than 6 months. Clinical manifestations, laboratory results, echocardiographic findings, treatment and outcome were compared between these 2 groups. Results: Clinical manifestations (hydrops of gallbladder: 0% versus 16%, P < 0.001) and laboratory results (white blood cell count 21,740 ± 11,706 versus 11,830 ± 4390/mm³, P < 0.001; hemoglobin 9.98 ± 1.25 versus 10.8 ± 1.37 g/dL, P = 0.015; platelet 483 ± 393 versus 355 ± 138 X 1000/mm³, P = 0.011; triglyceride 138 ± 77.5 versus 107 ± 17 mg/dL, P < 0.001) were different between patients with Kawasaki disease younger and older than 6 months, respectively. Younger infants were more likely to have incomplete presentation (35% versus 12%, P = 0.025), coronary involvement (65% versus 19%, P < 0.001), late intravenous immunoglobulin treatment and relatively poor outcome. Conclusions: Infants younger than 6 months with prolonged unexplained febrile illnesses should be suspected as having Kawasaki disease, despite the incomplete clinical presentation. Because early diagnosis and timely treatment are difficult in younger infants with Kawasaki disease because of delayed and incomplete clinical presentations, echocardiogram becomes an important implement for diagnosis. Early intravenous immunoglobulin treatment is required in view of the highest risk of coronary involvement in them.