The current diagnostic manuals, DSM-IV-TR and ICD-10, do not allow the diagnosis of ADHD to be made separately in the presence of autism (pervasive developmental disorder). However, the characteristics of ADHD are very common in autism, occurring in around 30 to 70%. Surveys of children with ADHD also reveal a high proportion of features of Autism Spectrum Disorder (ASD). Furthermore, treatment of ADHD in the presence of autism is of benefit in a large proportion. The inconsistency in the diagnostic manuals should be resolved in the forthcoming DSM-5 and ICD-11. The results of twin studies have been consistent with the sharing of genetic influences between autism and ADHD symptoms. Genome-wide studies have also shown shared chromosomal regions of interest for susceptibility sites for both conditions. There is an overlap between the executive function deficits in both conditions, although the details of the dysfunction may be different. There is evidence that all the standard treatments for ADHD can be effective in the presence of autism (though to a lesser extent than in pure ADHD): methylphenidate, amphetamines, atomoxetine, clonidine and guanfacine. Atypical antipsychotics such as risperidone and aripiprazole may be of specific importance in managing ASD with irritability, aggression and hyperactivity. The idea that ADHD cannot be diagnosed or treated successfully in those with ASD is a myth that should be dispelled; many of those who have both autism spectrum disorder and ADHD can benefit greatly from the treatment of the ADHD.
Santosh et al. (Sat,) studied this question.