Emotional, Behavioural and Social Correlates in Subthreshold and Full-Syndrome ADHD

Subthreshold attention-deficit/hyperactivity disorder (ST-ADHD) describes individuals who exhibit clinically significant symptoms of inattention, hyperactivity or impulsivity without meeting full diagnostic criteria for ADHD. Despite its subclinical status, ST-ADHD may be associated with substantial emotional, behavioural and social impairment. This study aimed to compare children and adolescents with ST-ADHD and full-syndrome ADHD in terms of emotional and behavioural difficulties and psychiatric comorbidities. This cross-sectional retrospective study included 217 patients with full-syndrome ADHD and 111 with ST-ADHD. Emotional, behavioural and social functioning were assessed using the Strengths and Difficulties Questionnaire (SDQ). Group differences were evaluated after controlling for potential confounding factors, including age, sex and education level. Interaction analyses were also performed to examine whether these differences varied by age or sex. Age distributions were comparable between the groups, although sex ratios and education levels differed. Psychiatric comorbidity was more prevalent in the ADHD group than in the ST-ADHD group (74.2% vs. 60.4%, p = 0.010). In covariate-adjusted analyses, hyperactivity/inattention scores remained significantly higher in the ADHD group, whereas emotional problems, conduct problems and peer-related difficulties did not differ significantly between the groups. Formal interaction analyses did not show significant Group × Age or Group × Sex effects. The observed functional difficulties and relatively high comorbidity rates suggest that ST-ADHD may represent a clinically relevant condition and that a dimensional assessment approach incorporating developmental and clinical characteristics may be useful. However, given the absence of a non-ADHD comparison group, these results should be interpreted cautiously. Future studies including typically developing children and psychiatric comparison groups are needed to further clarify the specificity of these difficulties.