Onychophagia in Obsessive–Compulsive Disorder (OCD): Prevalence and Clinical Characterisation

Introduction: Onychophagia, commonly known as nail-biting, is a chronic and repetitive behaviour disorder characterised by a compulsive/habitual nature. Obsessive–compulsive disorder (OCD) and onychophagia present a noteworthy intersection in clinical psychiatry. With a paucity of clinical investigations on this topic, we decided to perform a study on onychophagia in OCD. Materials and Methods: In this cross-sectional investigation, the sample comprised patients (aged 18 years and older) having a primary diagnosis of OCD (DSM-5) and a score on the Yale–Brown Obsessive–Compulsive Scale of at least 16 (moderate OCD). Individuals were referred to the Department of Neuroscience at the University of Turin. Analysis of the data was performed using JASP (Version 0.16.3), a freely available statistical programme created by the University of Amsterdam (JASP Team, 2022). Statistical value was set at p < 0.05. Results: Our sample consisted of 603 individuals with OCD, and onychophagia was present in 52 of the cases, with a prevalence of 8.6% (95% CI: 6.5–11.2%). Individuals with OCD and onychophagia had some specific clinical features compared to patients with only OCD. The main difference was detected in terms of the presence of autism spectrum disorder (ASD): in the group of patients having OCD and onychophagia, a prevalence of ASD as high as 96.2% was identified, compared to 18.0% in the OCD-without-onychophagia group. Discussion: Onychophagia is a relatively common problem in patients with OCD, with almost one individual out of ten experiencing this issue. OCD and onychophagia, when both present, might define a peculiar clinical phenotype with specific characteristics. The extremely high frequency of ASD in patients with OCD and onychophagia (96.2%) might be very useful information for clinicians, who should pay particular attention to screening for autism in this cohort of individuals.