This is the first study to have systematically investigated the interrelations between OC, ADHD, and autism symptoms in adult OCD patients. As expected, OCD patients presented with higher scores on ADHD and autism symptoms than normal controls. OCD + ADHD patients showed higher autism scores on most autism subscales than OCD − ADHD patients, although no between-group differences in OC symptom severity were found. These findings are in line with earlier findings in pediatric OCD, and suggest an interrelatedness of ADHD symptoms with autism symptoms in OCD (Ivarsson and Melin 2008
A substantial relationship between ADHD (particularly the inattentive and combined subgroups) and autism symptoms has not only been found in clinical OCD samples (as in the present study) but also in ADHD clinical as well as population-based samples (Reiersen et al. 2007
). Family research has indicated that autism traits, particularly in males with ADHD, might represent a familial trait that is partly shared with ADHD (Mulligan et al. 2009
). Thus, although according to DSM IV classification, ADHD and autism diagnoses are considered to be mutually exclusive, a growing body of literature (including the present small scale study) indicates that this classification rule does not hold. Moreover, autism and ADHD symptoms seem to share commonalities with OCD dimensions as well.
The interrelatedness between ADHD and autism symptoms within our OCD sample might reflect symptom overlap across the co-morbid disorders. Particularly the AQ attention switching subscale was highly correlated with the inattention subdomain of ADHD. Inspection of the wording of the items revealed seemingly contradictory relations between AQ attention switching and ADHD inattention: whereas inattention is expressed by the difficulty to sustain attention on a given task (e.g. “easily distracted because of external stimuli”), attention switching problems are expressed by the difficulty to divert attention between tasks (e.g. “I frequently get so strongly absorbed in one thing that I lose sight of other things”). Although seemingly contradictory, ADHD patients have repeatedly been found to exhibit both difficulty in attention switching (related to hyperfocusedness) and attention problems (Cepeda et al. 2000
; Oades and Christiansen 2008
). In this study, AQ problems with attention switching and ADHD inattention proved to be the strongest predictor for OC symptom severity, and of all OC symptom dimensions except hoarding. Therefore, AQ attention switching problems and ADHD inattention might well be at two ends of the same underlying attention problems.
The social skills subscale of the AQ showed significant correlations with both ADHD scales and OC symptom dimensions. Deficits in social skills have been found, both in OCD (Cath et al. 2008
) and in ADHD (Reiersen et al. 2007
). Thus, apart from the potential artifacts introduced by symptom overlap in measurements between the co-morbid disorders, ASD, ADHD and OCD might share substantial etiology. Therefore, it would be worthwhile to reconsider the DSM-IV exclusionary classification of these disorders. In support of this, recent comparative studies between children with ASD and ADHD indicated that ASD children show differences as well as similarities on executive function when compared to ADHD and OCD children. Executive function refers to those neuropsychological processes that involve planning, strategic organization of complex processes, flexible adaptation to novel stimuli, ability to shift mental sets, to inhibit irrelevant (motor) responses, and to engage in trial and error learning (Purcell et al. 1998
). Although substantial overlap existed between ASD and ADHD children, in general ASD children performed worse than ADHD children on tasks of planning and flexibility, whereas ADHD children were worse on motor inhibition tasks and spatial working memory tasks, (Sinzig et al. 2008
). Interestingly, OCD patients (Greisberg and McKay 2003
; van den Heuvel et al. 2006
) and in some instances their first degree relatives show problems in both domains; planning deficits comparable to ASD (Delorme et al. 2007
), and impaired motor inhibition on similar tasks as found in ADHD patients (Sinzig et al. 2008
; Chamberlain et al. 2007
). Thus, OCD patients and their relatives seem to share executive function problems, both with ADHD and ASD patients, strongly suggesting overlapping etiologies between the disorders. Therefore, to study common etiologies among OCD, ADHD and ASD patients, an endophenotypic family-based approach is warranted in which executive function associated with underlying genetic mechanisms is studied in OCD, ADHD and ASD in concert.
Our hypothesis that hoarding symptoms were related with autism symptoms was not confirmed. Although significant, correlations between hoarding and AQ scores were lower than between other OC dimensions and AQ. Further, autism scores did not predict hoarding symptoms, but hoarding seemed to be related with inattentiveness and with older age rather than with autism symptoms, which is in line with the literature. Problems with focused attention, coupled with problems in decision making, categorization, and planning, have frequently been described in hoarders (Saxena 2008
). With respect to age, the frequency and recognition of hoarding behavior is substantially increased among persons over 40 years of age (Samuels et al. 2008
). Thus, this co-morbidity pattern, i.e. the association between attention problems rather than autism symptoms and hoarding on the other hand, suggests that—in line with the literature—hoarding constitutes a phenotype that is in several (but not all) aspects discrete from the other OC symptom dimensions (Abramowitz et al. 2008
; An et al. 2009
). However, no definite conclusions can be drawn from this purely descriptive study, since the hoarding subscale entails two Y-BOCS symptoms only, which hampers the sensitivity to pick up real differences.
The finding that the AQ lack of social skills scale was associated with OC symptom severity was in line with previous findings (Cath et al. 2008
). Lack of social skills in OCD might reflect subtle impairments in theory of mind related functioning, a core feature in autism patients. Interestingly, theory of mind dysfunction is related to dysfunctions in set shifting and planning skills in children with autism (Pellicano 2007
), and—although not investigated—might also be present in OCD patients at the severe end of the spectrum.
Contrary to our expectation, the AQ attention to detail subscale exhibited low correlations with OCD, and did not turn out to be a significant predictor of OC symptoms or severity. Apparently, the AQ attention to detail subscale taps on a trait that differs from perfectionism, a trait known to be closely related to (some forms of) OCD (Myers et al. 2008
). Although patients are known to show enhanced attention for details related to OCD-relevant topics, these data suggest that in general, rather than scanning stimuli with great care to detail, OCD patients suffer from attention problems.
Recent research on memory distrust in OCD has found that OCD patients exhibit lack of confidence in their own perception, attention and memory, without clear evidence for an objective memory deficit (Hermans et al. 2008
; Radomsky et al. 2001
; Radomsky and Rachman 1999
). Moreover, the repetitive behaviors of OCD seem to weaken memory trust (Van den Hout and Kindt 2004
). However, the cause of the initial low confidence of OCD patients in their own memory capacities is unclear. Our findings of inattention and attention switch problems in OCD patients raise an interesting possibility, i.e. that these problems may, at least partially, be responsible for the low confidence of OCD patients in their cognitive processes. Difficulties in the management of attention may serve as a common factor between OCD, ADHD and ASD symptoms and explain the pathological doubt/uncertainty that seems to characterize these disorders.
These findings have several implications for treatment. First, considering that inattention as found in this study is central to OC symptoms, one would expect that addition of Methylphenidate to treatment in OCD patients with co-morbid ADHD symptoms will enhance treatment efficacy. Future treatment studies should be directed at exploring this. Further, several behavioral strategies such as task concentration training that have been found to improve attention in ADHD patients (O’Connell et al. 2008
; White and Shah 2006
) could be added to behavior therapy in OCD patients, and might improve treatment efficacy particularly in OCD + ADHD patients. Another implication for clinical practice involves the importance of assessment of autism symptoms in the treatment of OCD. Possibly, increased autism symptoms complicate treatment and limit treatment gains. Cognitive-behavior therapy with patients with increased autism symptoms might demand longer duration, and require adaptations of standard treatment protocols. Further research of the effect of autism symptoms on treatment response to OCD is needed to confirm these hypotheses.
Such ideas are further strengthened by the lack of social skills as reported by the OCD patients, a finding that implies that adding a social skills improvement module to standard cognitive behavior therapy for OCD might increase overall treatment efficacy in OCD, as was recently suggested by Cath and colleagues (Cath et al. 2008
Limitations of the present study include its descriptive nature, which precludes causal conclusions. Further, each symptom domain was measured by a single screening instrument. The measurement of ASD symptoms through self report alone is particularly problematic. Patients with complaints in the domain of self-reflection might be less able to reflect on their behavior. Further research should be conducted using multiple measures of the symptom domains of OCD, ADHD, and autism. Moreover, we suggest the use of more elaborated hoarding scales in future research, to further study relationship between autism and hoarding. The relations between pathological doubt and attention difficulties also need future exploration.
In conclusion: OCD patients exhibit increased rates of ADHD, and autism symptoms Problems with attention switching seems to be a strong predictor of OC severity and OC symptom dimensions, and might explain the lack of confidence in ones’ own cognitive processes that are typical for OCD. Future research with various assessment measures, using a family-based paradigm across the OCD, ADHD and ASD phenotype, might help us to better understand the complex relationships between OCD, ADHD and ASD.