More than a half of patients with OCD are classified as early‒onset. Early‒onset OCD has been indicated to be associated with a greater OCD global severity and more frequently comorbid with tic disorders and other obsessive‒compulsive（OC）spectrum disorders, compared with late‒onset OCD. Early‒onset OCD patients with severe impairment caused by both OC symptoms and comorbid OC spectrum disorders may be identified as being refractory.
 Tic disorders and autism spectrum disorder（ASD）are child and adolescent psychiatric disorders included in OC spectrum disorders.
 OCD comorbid with chronic tic disorders including Tourette syndrome（TS）is specified as tic‒related OCD. Tic‒related OCD is characterized by the high prevalence of early‒onset and sensory phenomena including“just right”feeling. Self‒injurious behaviors（SIB）such as head banging and body punching often occur in patients with TS. The patients’ concern about SIB is likely to trigger them, suggesting that an impulse‒control problem is a feature of TS. More than a half of patients with TS have OC symptoms. When OC symptoms in patients with TS were assessed with a dimensional approach, symmetry dimension symptoms were found most frequently over the lifetime. On the other hand, the severity of aggression dimension symptoms was the most stable during the course among all dimensions. Aggression dimension symptoms also exhibited a close relationship with impairment of global functioning and sensory phenomena. This tendency may be characteristic of tic‒related OCD.
 It is sometimes difficult to differentiate between OC symptoms and restricted, repetitive behaviors which are core symptoms of ASD. Recently, ego‒dystonia and insight are considered non‒essential to diagnose OCD, whereas high‒functioning and/or atypical ASD is recognized as being more prevalent than previously estimated. In this situation, attention to comorbidity of OCD and ASD is increasing, and the prevalence of OCD in children and adolescents with ASD was reported to be about 20％. One study on the impact of comorbid ASD in adults with OCD indicated that comorbid patients had higher scores for the Autism Questionnaire（AQ）subscales of attention switching and imagination but showed little difference in OC symptoms except for the predominance of compulsion compared to patients with pure OCD“. Just right”feeling and impulse‒control problems were evident in OC patients comorbid with both ASD and TS.
 Out of five adults with TS who underwent deep brain stimulation（DBS）because of refractory tics, four had impulse‒control problems including SIB, leading to very severe physical injuries in two patients. After DBS, tics and SIB improved in all patients；however, one patient experienced their re‒aggravation.
 To improve understanding of and treatment/support for refractory OCD, OC spectrum disorders should also be considered.