The literature on the overlap (co-morbidity) of attention deficit hyperactivity disorder (ADHD) with conduct disorder, specific learning disability, and anxiety disorders was reviewed to examine: (i) the evidence for ADHD being a syndrome distinct from the other conditions; and (ii) the evidence for co-morbid patterns representing meaningful subtypes of ADHD.
Narrative review of the literature.
Conduct disorder is distinguished from ADHD by prognosis, patterns of association and familial aggregation. ‘Pure’ disorders are uncommon, however, and there is little evidence to support a distinct co-morbid subtype. There are few data that reliably distinguish ADHD from specific learning disabilities, but there are weaknesses in research to date. A specific ADHD + learning disabled subtype may exist, but as yet the implications for treatment are not known. Attention deficit hyperactivity disorder is distinguished from anxiety by symptom discrimination, factor analysis, patterns of association, familial aggregation and treatment response. There is evidence for a distinct ADHD + anxiety subtype.