Epidemiological study of Landau-Kleffner syndrome (LKS) in Japan.

OBJECTIVE: We aimed to determine the incidence and prevalence of LKS in Japanese children.

METHODS: A questionnaire was sent to all 3004 Japanese hospitals that have a department of pediatrics. The questionnaire asked for the number of first-visit LKS patients and LKS patients who were followed up at or visited their clinic during the past one year Vital statistics of the same year (2008) published by Ministry of Health, Labor and Welfare, Japan were referenced to calculate the estimated incidence and prevalence of LKS among Japanese children.

RESULTS: Chiefs of 1562 pediatric departments answered our inquiry (51.9% of returns). Six chiefs had one new LKS patient, aged 6-14 years. Thirty two patients with LKS were followed in the same period. The number of children with LKS less than 20 years of age who needed medical care was at least 23 and at most 31. Vital statistics of Japan 2009 revealed that the population of children aged 5-14 years was 11,861,464 and that aged 5-19 years was 18,007,968.

DISCUSSION: The number of the first-visit LKS patients was 6 in a year. We estimated the incidence of LKS in the 5- to 14-years-old Japanese population as about 1 in 978,000. The number of LKS patients aged 5-19 was estimated to range from 44.2 to 59.6 among a population of 18,007,968. This means the prevalence of LKS under medical care is roughly one in 302,147-407,420 children aged 5-19. This study is the first epidemiological estimation of the incidence and prevalence of children with LKS in Japan or, for that matter, in any other area.

CONCLUSION: (1) Incidence of children with LKS aged 5-14 years was about 1 in a million in Japan. (2) Prevalence of children with LKS aged 5-19 and under medical care was one in about 300,000-410,000 in Japan. (3) This study constitutes the first epidemiological estimation of LKS in Japan.