Late-onset ADHD in adults: milder, but still dysfunctional

The requirement in classificatory systems that some impairment from attention-deficit/hyperactivity disorder (ADHD) symptoms starts before 7 years of age (age of onset of impairment criteria - AOC) has been harshly criticized. Although there is evidence that late-onset ADHD is a valid diagnosis, little is known about the role of age of onset of impairment on the clinical profile of adult patients.

The diagnoses of 349 adults with ADHD followed DSM-IV criteria. ADHD and oppositional defiant disorder (ODD) were evaluated with the K-SADS-E, and other comorbidities with the SCID-IV and the MINI. Subjects were divided in early and late-onset groups (age of onset of impairment between 7 and 12 years old). The effect of age of onset over clinical and demographic characteristics was tested by regression models.

Late-onset subjects were diagnosed later (P=0.04), had a lower frequency of problems with authority and discipline (P=0.004), and lower scores in SNAP-IV (P<0.001) and in Barkley's scale for problems in areas of life activities (P=0.03). On the other hand, late-onset patients presented a higher prevalence of comorbid general anxiety disorder (GAD) (P=0.01). Both groups had a similar profile in the remaining comorbidities and sociodemographic characteristics.

This study provides initial evidence that adults with late-onset ADHD have less severity, lower frequency of externalizing symptoms and increased comorbidity with GAD, but similar profile in other comorbidities. In addition, the data suggest that late-onset patients have a higher probability of delayed diagnosis despite the significant impairment of their condition.