Identifying Co-Occurring ADHD In Autism

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by persistent inattention, hyperactivity, and impulsivity that interfere with daily functioning.

There are three main presentations of ADHD: Predominantly Inattentive (ADHD-I), Predominantly Hyperactive-Impulsive (ADHD-H/I), and Combined (ADHD-C), which includes both inattentive and hyperactive-impulsive symptoms.

Autism Spectrum Disorder (ASD) is another neurodevelopmental disorder characterized by persistent differences in social communication and interaction, as well as restricted, repetitive patterns of behavior, interests, or activities.

ADHD and ASD frequently co-occur, with studies estimating that 30-70% of individuals with an ASD diagnosis also meet criteria for ADHD. This overlap can lead to significant challenges in diagnosis and treatment, as the symptoms of both disorders can interact and exacerbate each other.

Careful assessment is crucial to identify the presence of both disorders and develop appropriate interventions tailored to the individual’s unique needs.

Rau, S., Skapek, M. F., Tiplady, K., Seese, S., Burns, A., Armour, A. C., & Kenworthy, L. (2020). Identifying comorbid ADHD in autism: Attending to the inattentive presentation. Research in Autism Spectrum Disorders, 69, 101468. https://doi.org/10.1016/j.rasd.2019.101468

Key Points

The main findings of this study on identifying co-occurring ADHD in autism include:

• 61.8% of the clinic-referred sample of youth with diagnosed autism spectrum disorder (ASD) without intellectual disability (ID) met DSM-5 criteria for an attention disorder, with ADHD-Combined presentation being most common (76.8%), followed by ADHD-Inattentive (19.7%).
• Parent and teacher rating scales had greater diagnostic discriminability in identifying ADHD-Combined vs ADHD-Inattentive symptoms in cooccuring ASD. The ADHD Rating Scale IV inattentive symptom count provided the greatest discriminability.
• Factors like older age and higher inattentive symptom counts on the ADHD Rating Scale IV significantly predicted greater likelihood of ADHD-Inattentive diagnosis in ASD.
• The research highlights the need for thorough examination of inattentive symptoms to rule out ADHD-Inattentive in ASD, as rating scales provide limited discriminability compared to ADHD-Combined.

Rationale

ADHD commonly co-occurs with autism, with cooccuring rates ranging from 30-70% (Antshel, Zhang-James, Wagner, Ledesma, & Faraone, 2016; Joshi et al., 2017).

However, ADHD is often under-identified in this population, precluding access to appropriate treatment (Joshi et al., 2017).

Moreover, prior research suggests that commonly used ADHD rating scales may not adequately capture symptoms in ASD (Yerys et al., 2017).

The current study aimed to identify DSM-5 ADHD presentation prevalence rates in ASD without ID and determine which measures most effectively identify co-occurring ADHD symptoms to inform assessment practices.

Method

This study used archival neuropsychological assessment data from clinically-referred youth with an ASD diagnosis but without ID.

ADHD diagnoses were determined by licensed psychologists integrating data from parent/teacher questionnaires, clinical interviews, and neuropsychological tests.

A subset of 210 participants with complete parent/teacher data were further analyzed.

Procedure

Archival data from clinical and research-based assessments were used. Participants’ parents consented to data storage and de-identified use for research. Clinicians used a comprehensive assessment battery to determine ASD and ADHD diagnoses based on DSM-5 criteria.

Sample

The sample included 419 youth (76% male) aged 6-18 years (mean age 11.12) with autism spectrum disorder (ASD) and average overall intellectual functioning (mean FSIQ score of 99.18) referred for neuropsychological evaluation. 61.8% also met the criteria for co-occurring ADHD.

Measures

• ADHD Rating Scale-IV (ADHD-RS-IV): Parent and teacher versions were used to screen for the frequency of inattention and hyperactivity/impulsivity symptoms based on DSM-IV criteria.
• Child Behavior Checklist (CBCL) and Teacher Report Form (TRF): The Attention Problems and ADHD Problems subscales were used to assess ADHD-related symptoms and behaviors in home and school settings.
• Intellectual functioning measures: The Wechsler Intelligence Scales for Children (WISC-IV/V), Wechsler Adult Intelligence Scale (WAIS-IV), Differential Ability Scales (DAS-II), Wechsler Abbreviated Scale of Intelligence (WASI-II), Wechsler Preschool and Primary Scale of Intelligence (WPPSI-IV), and Reynolds Intellectual Assessment Scales (RIAS) were used to assess participants’ cognitive abilities and determine the presence or absence of intellectual disability.
• ASD measures: The Autism Diagnostic Observation Schedule (ADOS/ADOS-2) and Autism Diagnostic Interview-Revised (ADI-R) were used to confirm ASD diagnoses based on direct observation of the child’s behavior and comprehensive parent interviews regarding developmental history and current functioning.

Statistical Measures

Receiver operating characteristic (ROC) curve analyses compared diagnostic discriminability of measures. Area under the curve (AUC) values indicated diagnostic accuracy.

Venkatraman tests compared AUCs. Hierarchical logistic regressions examined unique variance explained by measures with meaningful AUCs.

Results

• 61.8% of the sample met DSM-5 criteria for ADHD. ADHD-Combined was most prevalent (76.8%), then ADHD-Inattentive (19.7%).
• Parent ADHD-RS-IV inattentive and hyperactive/impulsive symptom counts and CBCL/TRF ADHD Problems subscales had greatest discriminability for ADHD-Combined (AUCs>.70). Only parent ADHD-RS-IV inattentive symptoms meaningfully differentiated ADHD-Inattentive (AUC=.71).
• In logistic regressions, parent ADHD-RS-IV inattentive symptoms significantly predicted ADHD-Inattentive diagnosis beyond age effects. For ADHD-Combined, parent ADHD-RS-IV inattentive symptoms and TRF ADHD Problems added incremental predictive power.

Insight

This study provides important insights into the prevalence of ADHD presentations in ASD and the effective use of rating scales in identifying co-occurring symptoms.

The high co-occurrence rates, especially of ADHD-Combined presentation, highlight the need for routine ADHD screening in ASD.

However, the limited discriminability of most scales for ADHD-Inattentive symptoms suggests clinicians cannot rely heavily on these questionnaires alone to capture inattention.

Instead, thorough examination through detailed clinical interviews, behavioral observations, and record reviews is needed. The findings extend prior work indicating ADHD rating scales operate differently in ASD (Yerys et al., 2017) by demonstrating their variable utility across presentations.

Future research should examine item-level scale performance and compare additional measures like the BASC-2 in cooccuring ASD-ADHD.

Strengths

This study had several methodological strengths, including:

• Large, well-characterized clinical sample with expert clinicians determining ASD and ADHD diagnoses
• First study to examine DSM-5 ADHD presentation prevalence in ASD and compare diagnostic accuracy of common rating scales
• Use of both parent and teacher report
• Examination of rating scales’ incremental validity in predicting ADHD diagnosis

Limitations

Despite strengths, this study also came with several limitations, including:

• Use of clinically-referred sample may limit generalizability to community populations
• Criterion contamination, as the measures examined were also used by clinicians to inform diagnostic decisions
• Only two ADHD rating scales compared; other relevant measures like the BASC-2 not included
• Cross-sectional design precludes examination of long-term predictive validity of measures

Implications

The high prevalence of co-occurring ADHD in ASD underscores the importance of screening for ADHD symptoms in this population to inform treatment planning.

However, the results suggest rating scales alone are insufficient, especially for identifying ADHD-Inattentive presentation.

Clinicians evaluating ADHD in ASD should use rating scales in combination with detailed clinical interviews and observations to capture inattentive symptoms.

The study also highlights the need for further research to refine ADHD rating scales for use in ASD and examine their long-term predictive validity.

Improved assessment can ensure autistic individuals with cooccurring ADHD receive appropriately tailored interventions and supports.

References

Primary reference

Rau, S., Skapek, M. F., Tiplady, K., Seese, S., Burns, A., Armour, A. C., & Kenworthy, L. (2020). Identifying comorbid ADHD in autism: Attending to the inattentive presentation. Research in Autism Spectrum Disorders, 69, 101468. https://doi.org/10.1016/j.rasd.2019.101468

Other references

Antshel, K. M., Zhang-James, Y., Wagner, K. E., Ledesma, A., & Faraone, S. V. (2016). An update on the comorbidity of ADHD and ASD: A focus on clinical management. Expert Review of Neurotherapeutics, 16(3), 279–293. https://doi.org/10.1586/14737175.2016.1146591

Joshi, G., Faraone, S. V., Wozniak, J., Tarko, L., Fried,Joshi, G., Faraone, S. V., Wozniak, J., Tarko, L., Fried, R., Galdo, M., Furtak, S. L., & Biederman, J. (2017). Symptom Profile of ADHD in Youth With High-Functioning Autism Spectrum Disorder: A Comparative Study in Psychiatrically Referred Populations. Journal of Attention Disorders, 21(10), 846-855. https://doi.org/10.1177/1087054714543368

Yerys, B.E., Nissley-Tsiopinis, J., de Marchena, A. et al. Evaluation of the ADHD Rating Scale in Youth with Autism. J Autism Dev Disord 47, 90–100 (2017). https://doi.org/10.1007/s10803-016-2933-z

Keep Learning

Here are some reflective questions related to this study that could prompt further discussion:

• How might differences associated with ASD (e.g., social-communication difficulties, executive dysfunction) complicate the identification of cooccurring ADHD symptoms? What are strategies clinicians can use to disentangle traits?
• Given the limitations of rating scales in detecting ADHD-Inattentive symptoms in ASD, what other assessment methods could be helpful to identify inattention? How might these be adapted for use with ASD populations?
• How do you think co-occurring ADHD symptoms impact the day-to-day functioning of autistic individuals across home, school, and social contexts? What supports might help address impairments related to co-occurring ADHD?
• This study focused on school-aged autistic children and adolescents. What do you think are important considerations in assessing and treating co-occurring ADHD in autistic adults?