Profiles of Youth With Predominantly Inattentive Attention‐Deficit/Hyperactivity Disorder in a Nationwide Clinical Sample in Iceland

This study aimed to examine comorbidity, emotional symptoms, and cognitive profiles of youth with predominantly inattentive attention-deficit/hyperactivity disorder (ADHD-I) using a large nationwide clinical sample based on in-person assessments using gold-standard diagnostic procedures. Participants were 2109 children (64.7% male) aged 5-18 (M = 10.10) diagnosed with either ADHD-I (n = 636) or combined presentation (ADHD-C; n = 1473). Diagnoses of ADHD and comorbid psychiatric conditions were determined with the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime version (K-SADS-PL) and the Anxiety Disorders Interview Schedule for Children (ADIS-C/P). Additional measures included the Wechsler Intelligence Scale for Children (WISC-IV) and parent/teacher reports on the Strengths and Difficulties Questionnaire. Children with ADHD-I were, on average, 2 years older at the time of diagnosis than those with ADHD-C. Anxiety disorders, autism, depressive disorders, and tic/Tourette's disorder were equally prevalent across both the ADHD-I and ADHD-C groups. On cognitive testing, the ADHD-I group scored significantly lower on verbal comprehension (VCI), processing speed (PSI), and working memory (WMI) compared with the ADHD-C group. Findings highlight distinct challenges for youth with ADHD-I in this nationwide clinical sample. These youth are more often identified later and perform worse on certain cognitive tasks. Notably, they have a remarkably higher prevalence of comorbidities, such as anxiety disorders, than the worldwide prevalence of mental disorders in children and adolescents. The results underscore the importance of earlier screening and appropriate interventions for children presenting primarily with inattentive symptoms.