I assume you are talking about neuropsychiatric disorder such as ADHD, Tourettes, and neurodevelopmental disorders such as autism.  It is important to know that these disorders are common in the general population of children, so we do see children who may have BOTH JIA and a neurodevelopmental disorder. Research has not shown higher rates of ADHD or other neurodevelopmental disorders in children with JIA.   

There is some emerging research that is looking at disregulation of the immune system as a potential underlying cause of autism.  However, this is an emerging area of research and it is important for more study to be done on this before any conclusions can be drawn.