AN EXAMINATION REGARDING SUBTHRESHOLD CHARACTERISTICS OF ATTENTION DEFICIT HYPERACTIVITY DISORDER (ADHD) AND ITS CLINICAL IMPACT ON PSYCHOPATHOLOGICAL FEATURES AND TREATMENT OUTCOME OF OBSESSIVE-COMPULSIVE DISORDER (OCD)
Authors: Hosoi *Yukihiko , Mukai Keiichiro , Yokozumi Erisa , Ogino Shun , Sakurai Masahiko , Matsunaga Hisato 
Published: February 2025

Abstract

Background
The prevalence of attention deficit hyperactivity disorder (ADHD) in adult obsessive-compulsive disorder (OCD) patients has been reported to range from 5.5% to 52%. Conversely, adult ADHD patients are often associated with a variety of comorbidities including OCD. The reported prevalence of comorbidity of OCD in adult ADHD patients had varied widely in previous studies, ranging from 3%–44%. These findings regarding comorbidity indicate a bilateral linkage between OCD and ADHD, suggesting the possible existence of common biological bases for the development of the disorders.On the other hand, ADHD is considered as a complex disorder with clinical and genetic heterogeneity and elevated heritability, and childhood ADHD symptoms fulfilling diagnostic criteria often improve with age. Thus, it is clinically meaningful and useful to regard the continuous nature of ADHD psychopathology as widely variable, ranging from a diagnostic entity to a trait with subthreshold ADHD conditions in general and clinical populations. Indeed, it can be assumed that there may be a population of OCD patients with ADHD traits, even if they do not meet the diagnostic threshold for ADHD.

Aims
In this study, we sought to clarify the subthreshold characteristics of ADHD examining validity or clinical utility of the ADHD-trait group defined by the ADHD index score on CAARS in the OCD population.

Methods
We assessed lifetime comorbidity of ADHD using a structured diagnostic interview on the basis of DSM-5 diagnostic criteria in 87 adult Japanese patients with OCD. Additionally, we used the Japanese version of Conners’ Adult ADHD Rating Scales to assess the characteristics and severity of ADHD in each participant. According to the results, we divided these subjects into 3 groups; OCD subjects in the ADHD+ group were determined as having comorbid ADHD during their lifetime, along with the ADHD index score &gt;65 at the initial assessments. the ADHD-trait group was assigned by the finding that they did not have lifetime ADHD but who exceeded the threshold of the ADHD index, and others that exhibited the ADHD index below the threshold score were included in the non-ADHD group (ADHD− group). We compared these groups in terms of background profiles and clinical features, such as OCD symptomatology and psychometric test results. Additionally, the 6-month treatment outcome was compared prospectively between the groups.

Results
In the ADHD trait group (N=23), in addition to each subscale score on the CAARS distributed between the ADHD+ (N=14) and ADHD- (N=50) groups. the clinical features such as a higher impulsivity, a lower level of functioning, and increased prevalence of substance and/or behavioral addictions. were comparable to those in the ADHD+ group or in between those in the ADHD+ group and the ADHD- group, Moreover, the subjects in the ADHD+ group were significantly less responsive to the 6-month standard OCD treatments than those in the OCD- group, and the ADHD trait group showed intermediate responsivity.

Discussion
These results suggested the existence of possible continuous nature of ADHD pathology among the OCD patients, and also supported clinical utility and some validity of this group classification.