Attention-deficit hyperactivity disorder (ADHD) comorbidity: a case for "pure" Tourette syndrome?

More than a decade of research regarding the motoric characteristics of the attention-deficit hyperactivity disorder (ADHD) that accompanies Tourette syndrome has revealed unique anatomic and neurobehavioral differences and highlighted the importance of distinguishing children with this form from the 40% of children with Tourette syndrome who do not have ADHD. This distinction is important in providing guidance to parents and to patients and in formulating expectations for short- and long-term prognoses. In addition, study methodologies that fail to categorize patients in this way and instead involve covarying for dimensional symptoms of ADHD obscure biologically distinctive circuits and clinically meaningful patient characteristics.