Attention deficit hyperactivity disorder, combined type, dysthymic disorder and anxiety disorders: differential patterns of neurodevelopmental deficits.

The associations between neurodevelopmental deficits (NDD) and (1) attention deficit hyperactivity disorder, combined type (ADHD-CT) and (2) internalising disorders have been replicated. To date, the specific association between standardized NDD and carefully defined ADHD-CT alone, dysthymic disorder alone and anxiety disorders alone has not been systematically investigated in children of primary school age. A cross-sectional study of NDD in 99 six- to 12-year-old children with categorically and dimensionally defined ADHD-CT alone, dysthymic disorder alone and anxiety disorders alone and 20 age-matched healthy children was undertaken. The ADHD-CT and dysthymic disorder groups had increased total neurological subtle signs, compared to the anxiety disorders group, which, in turn, had increased total neurological subtle signs compared with the healthy children. Interestingly, the dysthymic disorder children had increased conjugate eye gaze difficulties compared with the other three groups. The differences remained after controlling for full scale IQ. These findings suggest a neurobiological underpinning of dysthymic disorder, while confirming that of ADHD-CT in primary school age children. Future studies will explore whether the above more specific neurological subtle signs are developmental phase specific or independent associations.