Diagnosis of Co-occurring Autism and Attention Deficit Hyperactivity Disorder

Autism and attention deficit hyperactivity disorder (ADHD) both have onset in early childhood and have multifaceted lifelong effects. The two conditions are separated by different core behavioural symptoms and clinical management. However, autism and ADHD have significant co-occurrence rates. Both autism and ADHD are associated with social differences, high sensory needs, attention difficulties and increased co-occurrence with other conditions. This has resulted in debate about whether autism and ADHD should be viewed as one condition on a gradient or as two separate conditions. Regardless of such the taxonomic classification issues, it appears that, in those children most affected by autism + ADHD characteristics, there are additive challenges across the behavioural and cognitive domains associated with both conditions.

Autistic and ADHD children both benefit from early support, which can reduce some of the negative outcomes associated with these conditions. However, the opportunities to access early support during a sensitive developmental period are reduced by the delayed diagnosis of autism that happens when ADHD co-occurs. A literature review conducted as part of this thesis established that this delay is observed across international jurisdictions. The literature review also demonstrated that there is evidence for an earlier ADHD diagnosis when autism is present. There was also some limited evidence for later age of parental first concern and longer wait time to diagnosis for the autism + ADHD group. Other characteristics which further exacerbated the delay were being female and an ADHD diagnosis being given before the autism diagnosis.

The literature review indicated an international pattern in delayed diagnosis of autism for autistic + ADHD children and that there did not appear to be any studies examining the diagnostic pathway for these children in New Zealand. Therefore, understanding whether this delay is relevant for autistic + ADHD children in New Zealand is an important area of study. As is a further understanding of the mechanism by which autism + ADHD children might present differently to children with a singular diagnosis of either autism or ADHD. Variables indicated by the literature review, such as wait time to diagnosis and age of parental first concern, were also explored as possibly contributing to delay in autism diagnosis when ADHD was present. In the first study of this thesis, 288 New Zealand parents of children diagnosed with autism (n = 111), ADHD (n = 93), or both conditions (n = 84) participated in an online survey. The results indicated that co-occurring autism and ADHD was associated with an earlier ADHD diagnosis and a later autism diagnosis in New Zealand, thus fitting the international trend. Parents of children with both diagnoses reported less atypical development in language and social behaviours compared to parents of autistic children. The co-occurring group also experienced longer times to diagnosis, and saw more types of specialists prior to a diagnosis than those with autism.

The experience of parents might also enhance an understanding of delays and challenges in the diagnostic process. Therefore, the second study of this thesis used qualitative reflexive-thematic analysis to understand the experiences of parents on their journey to diagnosis for their children. The findings suggest that parents view the process to diagnosis as an adversarial one, which required extensive knowledge, finances, and network resources. Parents also described a second ‘battle’, which was often unexpected, to get support for their child post-diagnosis. Parents identified that the relief of the removal of parenting guilt and blame, as well as situating the issue outside of the child, was an important part of the diagnosis label.

The literature review and both studies one and two indicated that the diagnostic process for autism + ADHD is complex. In the final study, these complexities were further explored by an anonymous online survey of clinicians' (psychologists, paediatricians, psychiatrists) responses (n = 29) to two complex neurodevelopmental cases described in vignettes. These vignette cases included autism + ADHD characteristics and a number of other co-occurring characteristics. Clinicians reported multiple possible lines of inquiry including specific assessments for particular hypothesised diagnoses and more general assessments. The results of this study suggested that complex cases require lengthy consideration and multiple resources.

The thesis identified and elucidated the phenomena in the timing of diagnosis when autism and ADHD co-occur. This included understanding the delay in autism diagnosis when ADHD is present and provided possible evidence for where along a diagnostic pathway such a delay might be occurring. A biopsychosocial framework was also used to consider multiple psychological and social aspects of this process including the experiences of complex neurodevelopmental cases for families and clinicians. The experience for families and clinicians grappling with an imperfect diagnostic model suggests that multiple resources, time delays and stressful situations are common. This thesis concludes with theoretical and practical recommendations for an improved diagnostic pathway and experience for clinicians and families.