Objective Neuropsychological studies have highlighted the presence of specific cognitive deficits in two neurodevelopmental disorders affecting more commonly male children and often presenting in co-morbidity, Tourette syndrome (TS) and attention-deficit and hyperactivity disorder (ADHD). It is estimated that over 60% of children with TS present with co-morbid ADHD and the assessment of the relative contribution of tic symptoms and ADHD symptoms to cognitive problems in this patient population poses considerable challenges. We set out to determine the impact of co-morbid ADHD on cognitive function in male children with TS by conducting a controlled study with a comprehensive battery of neuropsychological tests.
Method Participants included four groups of unmedicated age- and gender-matched children (mean age 10–12 years, range 6–15 years; 85%–100% male gender): TS group (n=13 children with a diagnosis of uncomplicated or ‘pure’ TS), TS+ADHD group n=8 children with TS and co-morbid ADHD), ADHD group (39 children with ADHD in the absence of tics) and controls n=66 healthy children). All patients had a DSM-validated diagnosis and were recruited from the Child Neuropsychiatry Unit, Varese, Italy, whereas healthy controls were randomly selected from a pool of research volunteers from local schools. Following clinical assessment, each participant completed a standardised battery of neuropsychological tests: the Wechsler Intelligence Scale for Children-III (Block Design test, Vocabulary test), Italian Battery for ADHD (Walk-Don’t Walk test, Sustained Auditory Attention test, Stroop test, Sentence Completion test, Matching Familiar Figures test, Sustained Visual Attention test), Tower of London test, Corsi test, and Digit Span test.
Results All patient groups reported significantly lower scores than healthy controls across the neuropsychological tests involving executive functions. A specific pattern in cognitive performances emerged, showing that the TS+ADHD group was the most severely affected, followed by the ADHD group and the TS group. This was particularly evident from the results of the tests assessing planning ability (Block Design test, Matching Familiar Figures test, Tower of London test), inhibitory function (Walk-Don’t Walk test, Stroop test, Matching Familiar Figures test), working memory (Sustained Auditory Attention test, Corsi test, Digit Span test) and visual attention (Walk-Don’t Walk test, Matching Familiar Figures test, Sustained Visual Attention test), but not auditory attention (Sustained Auditory Attention test).
Conclusion Although problems in executive functions are more common in all patient groups than healthy controls, deficits in planning ability, inhibitory function, working memory and visual attention reported by children with TS appear to be more strongly related to the presence of co-morbid ADHD symptoms.