Nail biting in children with ADHD: exploring its clinical correlates, psychiatric comorbidities and association with other body-focused repetitive behaviors

This study investigated whether children with ADHD who engage in nail-biting (NB) differ clinically and cognitively from those who do not, focusing on body-focused repetitive behaviors (BFRBs), psychiatric comorbidities, and cognitive profiles. In this retrospective, cross-sectional chart-review study, 250 medication-naive children aged 8–12 years with ADHD were grouped by the presence ( n = 100) or absence ( n = 150) of NB. Co-occurring BFRBs, psychiatric comorbidities, cognitive performance (WISC-R subtest scaled scores) and symptom severity (RCADS-P, CPRS-R: S) were compared using Mann–Whitney U and chi-square tests, followed by multivariable binary logistic regression. Compared with children with ADHD without NB, those with NB showed higher rates of co-occurring BFRBs (thumb sucking, lip or cheek biting, bruxism), anxiety disorders, obsessive–compulsive disorder and speech disorders, and substantially higher parent-rated internalizing symptoms (RCADS-P Total Anxiety and Depression, r rb = 0.55). They also obtained lower scores on selected WISC-R subtests, most consistently Vocabulary, Comprehension, Picture Completion and Picture Arrangement. In multivariable analysis, older age, higher internalizing symptoms and lower scores on these subtests were independently associated with NB. In children with ADHD, NB and co-occurring BFRBs were associated with a greater burden of internalizing symptoms and with lower performance on selected verbal and perceptual WISC-R subtests, and may correspond to a distinct clinical profile. These associations are cross-sectional and correlational and do not imply causality.