Original articleA nationwide survey of opsoclonus–myoclonus syndrome in Japanese children
Introduction
Opsoclonus–myoclonus syndrome (OMS) is a rare autoimmune disease of childhood that is characterized by opsoclonus, myoclonus, ataxia, and behavioral changes such as irritability and sleep problems [1], [2]. Opsoclonus is a specific abnormal eye movement characterized by the rapid, conjugate, multidirectional, and chaotic eye movements [2], [3], and is occasionally accompanied by myoclonic jerks and ataxia. In children, about 50% of OMS cases are accompanied by occult neuroblastoma [2], [4], [5], [6], [7]. The mechanisms of OMS are believed to be paraneoplastic immune-mediated encephalopathy; however, its detailed pathogenesis and epidemiology in Japan remains unclear. In this study, we investigated the epidemiology, clinical features, treatment, and outcome of OMS in Japan, in order to find more appropriate treatments for refractory OMS.
Section snippets
Nationwide survey
We sent the first survey questionnaires to all 939 medical hospitals having department of pediatrics and more than 20 beds for patients in Japan. Of 626 responses (recovery rate: 67%), the second questionnaires were sent to the hospitals, where OMS patients were managed (Fig. 1). The institutional review board of Yamaguchi University Hospital approved this study (H26–46). The data set used in this study consisted of anonymized data, so that individual identifying information could not be
Results
We identified 23 OMS patients in Japan 2005–2009, as shown in Table 1. The male/female ratio was 10/13, median age was 54 months (range: 24–160 months), and the median age at the onset of disease was 16.5 months (range: 11–152 months). The incidence peaked at 12–24 months of age (Fig. 2). Ten patients had neuroblastoma (43.5%). Nine patients had infections before the onset of OMS (39.1%) (mycoplasma: 1, exanthema subitum: 1, hand-foot-mouth disease: 1, varicella: 1, acute gastroenterocolitis: 1,
Discussion
This is the first nationwide survey of OMS in Japan. The present study determined 23 OMS patients in the Japanese children (average number of children less than 15 years old 2005–2009: 17,287,000) over 5 years. The annual incidence of OMS was 0.27 patients in children, per million per year in Japan. Corrected for the recovery rate of this survey, these figures are estimated 0.40 patients. There are several reports on the incidence and characteristics of OMS in other countries [4], [5], [10], [11]
Acknowledgements
We would like to thank T. Naito and N. Azuma (Saiseikai Kawaguchi General Hospital), T. Tsuru and A. Ohba (Matsudo City Hospital), N. Sugiyama (Tokai University Hospital), H. Matsuura (Jusendo Hospital), T. Yamaue (Tokushima Municipal Hospital), K. Furuhashi (Hamamatsu University Hospital), S. Yamashita (Kanagawa Children’s Medical Center), T. Shiihara (Gunma Children’s Medical Center), N. Ishikawa (Hiroshima University Hospital), H. Torisu (Kyushu University Hospital), S. Suenobu (Oita
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