Self-reported symptoms of attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and affective lability in discriminating adult ADHD, ASD and their co-occurrence.

Background: To diagnose and manage adults with Attention Deficit Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), or their co-occurrence (ADHD + ASD), clinicians must identify specific features that differentiate these diagnostic categories. Self-report questionnaires targeting specific features are widely used and, together with clinical assessments, provide reliable diagnoses. Although affective lability is present in various psychiatric disorders, it lacks specificity when screening for ADHD in the general population, and its discriminant value for ADHD, ASD, and ADHD + ASD has not been studied.

Methods: This study involved 300 adults without intellectual developmental disorder (188 male) who received an ADHD (n = 174), ASD (n = 68), or ADHD + ASD (n = 58) diagnosis after a multidisciplinary consensus decision according to DSM-5 criteria. Before clinical assessment, all patients requesting evaluation for one of these diagnoses completed questionnaires on an online platform. The assessment instruments included a modified version of the Barkley Adult ADHD Rating Scale (BAARS IV) for ADHD, the Autism Spectrum Quotient (AQ) and the Empathy Quotient (EQ) for ASD features, and the Affective Lability Scale (ALS) for affective lability. Total scores and sub-scores of the instruments were compared among the three groups. Additionally, stepwise logistic regression analyses were conducted to identify specific measures that contribute to group discrimination.

Results: Results revealed distinct patterns in symptomatology as expected. The ADHD and the ADHD + ASD groups presented significantly higher ALS total score compared to ASD. Stepwise logistic regression analyses identified specific measures contributing to group differentiation. ASD vs. ADHD + ASD discrimination included BAARS IV current total score and EQ total score. The subscale anger from ALS in addition with BAARS IV past total score and AQ total score were the factors that discriminated ADHD diagnosis from the co-occurrence of ADHD and ASD. Finally, BAARS IV past total score, BAARS IV current inattention, AQ total score, and EQ total score were found to differentiate ADHD from ASD.

Conclusions: The study highlights the significance of incorporating emotional dimensions in diagnostic frameworks and may contribute valuable insights for clinicians differentiating neurodevelopmental conditions.