Behavioral and cognitive subtypes of ADHD.

Attention-deficit hyperactivity symptoms are observed by teachers in 9.2% of a nonreferred elementary school population. Two subtypes of attention-deficit hyperactivity disorder (ADHD), a cognitive form and a behavioral form, are identified. The behavioral subtype includes about 80% of those identified and is characterized by distinct clinical phenomenology of inattention, impulsivity, and hyperactivity. These children can be described on a continuum of severity, with the most severe showing behavioral features indistinguishable from conduct disorder. Children with behavioral subtypes of ADHD do not exhibit the specific skill deficits on neuropsychological tests that are characteristic of reading disabled children. There is a second, less prevalent type of cognitive attention-deficit hyperactivity disorder constituting approximately 20% of ADHD children that includes severe academic underachievement along with inattention, impulsivity, and overactivity. Children with the cognitive subtype exhibit information processing deficits that involve inadequate encoding and retrieval of linguistic information, characteristic of reading disabilities.