Exploring the Nature of ADHD Comorbidity in Tic Disorders

Introduction: Tic disorders (Tics) are childhood-onset neurodevelopmental conditions, and approximately half of this population also have an ADHD diagnosis. Some of the clinical symptoms of Tics resemble ADHD which could explain the high comorbidity rate. Objectives: This research aims to investigate if the ADHD symptoms seen in children with both Tics and ADHD (Tics+) are true comorbid ADHD or a result of their Tics. Methods: Participants from a community-based study of children aged 6-18 reported their ADHD symptoms using the Strengths and Weaknesses of ADHD Symptoms and Normal Behavior Scale (SWAN). Their cognitive control was assessed using the Stop Signal Task. The symptom profiles of those with Tics and no ADHD diagnosis (Tics-, n=192), ADHD (n=2416), Tics+ (n=119) and controls (n=31908) were compared using logistic regressions. A linear regression model was used to determine if Tics+ was associated with greater cognitive control deficits, a well-established correlate of ADHD. Results: Tics+ demonstrated higher ADHD traits, specifically for hyperactive symptoms (p<0.001). 6 of 9 hyperactive symptoms were reported at significantly higher rates in Tics+ compared to ADHD. Cognitive control was equal between Tics+ and ADHD while both groups had significant deficits compared to Tics- and controls. Conclusion: Children with Tics+ have more hyperactive symptoms which were not associated with worse cognitive control than ADHD. The cognitive control deficits observed in Tics+ were consistent with a true comorbid ADHD. It is of interest to explore shared risk factors to explain the high prevalence of ADHD among this group.