Effect of Comorbid ADHD on IQ and Adaptive Behavior in Children with ASD: Implications for Outcomes and Treatment

Background:  The conceptualization of ASD as a comorbid disorder with ADHD has been surrounded by controversy.  The paucity of studies that compare comorbid patterns in children with ASD has added to such debate, specifically in connection to ADHD.  Several reports show moderate to high ADHD prevalence among children with ASD, identifying ADHD as the most common comorbidity for this group of children.  A better understanding of the comorbidity between both entities should, therefore, give rise to an appropriate sequence of intervention goals.

Objectives:  The aim of this study was to establish comorbidity rates of ADHD in Venezuelan children with ASD and to describe clinical phenomenology in both groups (ASD and ASD+ADHD) and the implications of the comorbidity for treatment decisions.

Methods:  Diagnostic and demographic data for children between two and seven years of age were collected as part of an epidemiological study of autism in Venezuelan children.  The assessment protocol included the Raven’s Progressive Matrices Test and ADOS.  Parents completed the VABS and ADI-R.  Clinical manifestations of ADHD were evaluated using the Spanish version of the Conners’ Parent Rating Scale – Revised (CPRS-R). 

Results:  The assessment was completed by 103 children, of whom 65% (n=67) were diagnosed with ASD, while 35% (n=36) met criteria for an additional diagnosis of ADHD.  Among the comorbid cases, 23 (64 %) were of the combined subtype, 3 (8 %) predominantly inattentive, and 10 (28 %) predominantly hyperactive-impulsive.  Diagnosis was found to have no main effect on the ASD symptoms’ measures of communication (p=0.55), reciprocal social interaction (p=0.277), and play and stereotyped behaviors (p=0.112).  Diagnosis had a main effect on IQ (p=0.04); children from the comorbid group scored lower (86.71) than those from the pure group (90.62).  By contrast, diagnosis had no effect on the adaptive functioning measures: daily living skills (p=0.255), communication (p=0.109), and socialization (p=0.135).

 Conclusions:  The clinical presentation of ADHD in children with ASD has been found to be similar to the typical presentation of ADHD.  This is of paramount relevance due to the availability of treatment.  To date, there are few treatments for the core symptoms of ASD, while there is a wide scope of options for the treatment of ADHD.  Thus, when a child presents with both diagnoses, the identification of ADHD offers more comprehensive treatment options, which impact adaptive functioning and quality of life.  The results of this study reveal once again the heterogeneity of the clinical expression of ASD as a frequent phenomenon and not just the exception.  Our results suggest that, in pediatric mental health settings, the condition of comorbidity is expected between ASD and ADHD.  The data obtained do not support the idea of different clinical syndromes for ASD depending on the presence of an ADHD comorbid condition.