Studies in children with ADHD have reported lower test scores related to intellectual function, academic underachievement and greater problems in executive function compared with children without ADHD; however, research examining neurocognitive development in children with ADHD is limited. This current longitudinal study aimed to investigate the intellectual, academic and executive functions of children with a diagnosis of ADHD over a 4-year interval.
A total of 55 children with ADHD (diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders – 4th Edition),* primarily recruited from local outpatient health services between 1997 and 2001, were followed up for 4 years ± 4 months. The enrolled children completed a clinical interview assessing their perceptions of their behaviour, academic performance and relationships, while their parents and teachers completed semi-structured interviews and responded to questions related to the child and the severity of their ADHD. Children completed the same neurocognitive assessments at baseline and follow-up, and at follow-up they were categorised either as ADHD persisters (n=34) or as having ADHD in partial remission (n=21).† The neurocognitive assessments of the children with ADHD that were made at baseline and follow-up comprised the WISC-III, WRAT-III, ACPT, TMT, WCST, Verbal Fluency task and Design Fluency task.‡
The study reported that intellectual function was stable over the 4-year interval, although reliable change analyses highlighted variability in academic performance. A total of 51% of children showed a reliable decline in academic performance in ≥1 subject, with 20% having a reliable decline in academic performance in ≥2 areas. Conversely, 29% of patients showed a reliable improvement in academic performance in 1 subject, with 3.6% having a reliable improvement in academic performance in 2 areas. A significant decline was reported in spelling scores between baseline and follow-up (p=0.028), and a non-significant decline was observed in mean reading and arithmetic scores (WRAT-III) over the 4-year period (p=0.414 and p=0.286, respectively).
Age-standardised performance in executive function was generally stable or improved over time, and significant improvements were reported in measures of information processing, attentional control, cognitive flexibility and goal setting.
Baseline ADHD symptom scores and observer ratings of inattention/hyperactivity were generally similar between the persistent ADHD group and the partial remission group. Those with ADHD in partial remission had significantly higher Full Scale intelligence quotient (FSIQ) and Performance IQ (PIQ) scores (p=0.032 and p=0.007, respectively) than those with persistent ADHD. Scores in these domains increased over time in those with partial remission, but remained similar in those with persistent ADHD. Children with ADHD in partial remission also performed significantly better in WRAT-III arithmetic scores than those with persistent ADHD (p=0.019). Overall, there was some evidence of better neurocognitive performance in children with ADHD in partial remission at follow-up compared with those with persistent ADHD.
At follow-up, a significantly higher proportion of patients with persistent ADHD were receiving methylphenidate compared with those with ADHD in partial remission (73.5% vs 52.4%, p=0.005).
Limitations of this study included: 1) improvements in results may be due to practice effects as opposed to actual improvement; 2) sample size attrition between baseline and follow-up resulted in small sample size, and it is possible that the remaining sample was biased towards children with greater neurocognitive difficulties or persistence of symptoms; 3) under-reporting of symptoms may have occurred due to parents not being explicitly told to rate the child’s behaviour off medication.
The authors concluded that monitoring the academic performance of children with ADHD over time is important given the level of performance decline in children in this study despite the majority being prescribed stimulant medication at some point during the follow-up period. Over the assessment period, although intellectual and executive functioning remained stable or improved, respectively, academic performance decreased. A reduced symptom burden at follow-up was also noted to be associated with improved neurocognitive function.
*Patients were included if they received a diagnosis of ADHD at baseline, had an FSIQ of ≥70 on initial assessment and showed no evidence of neurological disorder or psychosis
†Persisters were those who continued to meet full ADHD criteria at follow-up (n=34), whereas those having ADHD in partial remission had <6 symptoms of inattention or hyperactivity/impulsivity in any setting (n=10) or displayed ≥6 symptoms of inattention or hyperactivity/impulsivity in one setting but no symptoms in a second setting (n=11)
‡ACPT, Auditory Continuous Performance Test; TMT, Trail Making Test – Children’s Version; WCST, Wisconsin Card Sorting Test; WISC-III, Wechsler Intelligence Scale for Children—Third Edition; WRAT-III, Wide Range Achievement Test—Third Edition
Murray AL, Robinson T, Tripp G. Neurocognitive and symptom trajectories of ADHD from childhood to early adolescence. J Dev Behav Pediatr 2017; Epub ahead of print.