Prevalence of ADHD Relatively Stable Over Time Despite Increase in Diagnoses

The actual prevalence of attention-deficit/hyperactivity disorder (ADHD) remained relatively stable over the course of a decade, even in the face of increases in clinical diagnoses, according to researchers who published their findings in The Journal of Child Psychology and Psychiatry. Despite small increases in subthreshold-ADHD and mean ADHD scores, they asserted that the combined results suggested that changes in a variety of factors were responsible for the apparent uptick, rather than a true increase in the ADHD phenotype.

Conflicting results from research over the last few decades have left the psychiatric community uncertain as to the actual trajectory of ADHD in the pediatric population. The study investigators were looking to help answer a pressing clinical question without a clear answer: Has the prevalence of ADHD truly increased over time?

Data on 19,271 9-year old twins (50.6% boys) were extracted between 2004 and 2014 from the ongoing population-based Child and Adolescent Twin Study in Sweden and analyzed for ADHD traits using the Autism-Tics, ADHD and other Comorbidities (A-TAC) inventory, via parental report. Cutoffs were established for diagnostic-level and subthreshold-level ADHD, and yearly mean ADHD scores were calculated and compared with ADHD lifetime prevalence of clinical diagnoses, derived from national patient registers. Odds ratio (OR) estimates were calculated based on these results.

Diagnostic-level ADHD (n=406, 2.1%) did not increase significantly in prevalence over a decade (odds ratio [OR] 1.37; 95% CI, 0.77-2.45; P =.233) despite an overall 37% elevation during this period. At the same time, both subthreshold ADHD prevalence (n=2058 [10.7%]) and mean ADHD scores did increase significantly over time (P <.001 for both measures). Meanwhile, ADHD clinical diagnoses increased considerably (>5-fold) over this same time period (OR 5.27; 95% CI, 1.85-14.96; P <.001). When stratifying patients by sex, investigators found that prevalence estimates were consistently lower for girls compared with boys across all measures.

Identified study strengths included a large sample size, extended study period, good response rates, excellent stability and validity of the Autism–Tics, ADHD, and other Co-morbidities inventory (A-TAC), and the use of a population-based sample.

Study limitations included declining participation in the study, which could have possibly skewed results, moderate sensitivity of the ADHD scale leading to potential underestimation of changes over time, use of only parental reports, not accounting for pharmacological treatment, and a question of whether results from this twin study were generalizable to the singleton population.

Given these findings, the investigators stated that the large increases in clinical ADHD diagnoses were unlikely to be representative of a real bump in prevalence. Rather, they suggested that such apparent inflations were likely reflective of the effect of a number of possible factors rather than a true elevation. These factors may include alterations in clinical diagnosis and treatment practices, more widespread community awareness of ADHD, changes in diagnostic reporting, better healthcare access, and/or the possibility that ADHD is being overdiagnosed. The investigators recommended further exploration to replicate their results using a variety of study designs to strengthen their findings.

Disclosures: HL has served as a speaker for Eli-Lilly and Shire and has received research grants from Shire all outside the submitted work. PL has served as a speaker for Medice. The remaining authors have declared that they have no competing or potential conflicts of interest.

Reference

Rydell M, Lundström S, Gillberg C, Lichtenstein P, Larsson H. Has the attention deficit hyperactivity disorder phenotype become more common in children between 2004 and 2014? Trends over 10 years from a Swedish general population sample [published online February 27, 2018]. J Child Psychol Psychiatry. doi:10.1111/jcpp.12882