Prevalence of nail biting and its chronological relationship with tics in child and adolescent outpatients with Tourette syndrome: a single-centre, retrospective observational study

OBJECTIVE: To evaluate the prevalence of nail biting in child and adolescent outpatients at a single institution and the chronological relationship between nail biting and tics in patients with Tourette syndrome (TS) with or without attention-deficit hyperactivity disorder (ADHD). DESIGN: Retrospective observational study. SETTING: Teaching hospital in Taiwan. PARTICIPANTS: All participants were aged 4–18 years, including 535 patients with TS, 230 patients with provisional tic disorder and 1460 patients without neurological or psychiatric disorders (controls). OUTCOME MEASURES: Presence of nail biting, starting age for nail biting and starting age for motor and/or vocal tics. RESULTS: Nail biting was more commonly observed in patients with TS (56.6%) than in patients with provisional tic disorder (27.4%) or controls (15.0%), regardless of sex (all p<0.020). Nail biting was also more common in patients with TS with ADHD than in those without (75.0% vs 47.6%; p<0.001), but the starting age was significantly later in those with concomitant ADHD than without (5.3 vs 3.8 years; p<0.001). In patients with TS, the onset of nail biting occurred earlier than that of tics, regardless of ADHD status. CONCLUSION: Nail biting was more prevalent and occurred earlier than tics in patients with TS, regardless of ADHD status, in the study population.