Prevalence of tic disorder in two schools in the Basque country: Results and methodological caveats.

Different studies have shown that the prevalence of tic disorder is highly variable, depending on the methodology employed. The aim of this study was to determine the prevalence of tic disorder among children of two schools. The study was conducted in three successive steps: information to parents and teachers by way of speeches and projection of videotapes; anonymous fulfilling of an ad hoc questionnaire by teachers and parents and identification of children as "possible tic disorder" according to the questionnaire; and confirmation of the presence of tics by direct observation of children at school (20 minutes in each classroom). Eight hundred sixty-seven children were included. Age ranged from 4 to 16 years. Ninety percent of parents and 99% of teachers fulfilled the questionnaire. Seventy-one children had tics according to parents' and 50 according to teachers' opinion (both coincided in 23 cases). Fifty-seven cases were identified after direct observation in the classroom (prevalence of 6.5%). The vast majority of tics were mild in severity and duration. Prevalence obtained in this study was comparable with data reported in studies using a similar methodology, which is higher than results shown in early studies addressed with less rigid methodology. Most of identified cases were quite mild, not leading to major functional disability. In spite of the methodology employed, it is possible that some cases were lost. Copyright 2006 Movement Disorder Society.