A case-controlled study of repetitive thoughts and behavior in adults with autistic disorder and obsessive-compulsive disorder.

The purpose of this study was to investigate the types of repetitive thoughts and behavior demonstrated by adults with autistic disorder and compare them with those of age- and sex-matched adults with obsessive-compulsive disorder. Fifty consecutive patients admitted to the Yale Adult Pervasive Developmental Disorders (Autism) Clinic with a primary diagnosis of autistic disorder (DSM-III-R and DSM-IV) completed the symptom checklist of the Yale-Brown Obsessive Compulsive Scale. Types of current obsessions and compulsions were evaluated. The comparison group consisted of 50 age- and sex-matched adults with obsessive-compulsive disorder (without tics) (DSM-III-R and DSM-IV). Direct discriminant function analysis showed that the patients with autistic disorder could be distinguished from those with obsessive-compulsive disorder on the basis of the types of current repetitive thoughts and behavior that they demonstrated. Compared to the obsessive-compulsive group, the autistic patients were significantly less likely to experience thoughts with aggressive, contamination, sexual, religious, symmetry, and somatic content. Repetitive ordering; hoarding; telling or asking (trend); touching, tapping, or rubbing; and self-damaging or self-mutilating behavior occurred significantly more frequently in the autistic patients, whereas cleaning, checking, and counting behavior was less common in the autistic group than in the patients with obsessive-compulsive disorder. In addition, a specific subset of seven obsessive-compulsive variables from the Yale-Brown Obsessive Compulsive Scale symptom checklist was identified that reliably predicted membership in the autistic group. These results suggest that the repetitive thoughts and behavior characteristics of autism differ significantly from the obsessive-compulsive symptoms displayed by patients with obsessive-compulsive disorder. Future studies are warranted to assess the treatment response and neurobiological underpinnings of repetitive thoughts and behavior in patients with autism and obsessive-compulsive disorder.