According to the National Institutes of Health, the comorbidity rates of ADHD and autism vary, estimating that 10-90% of autistic children also have ADHD. Several factors contribute to this wide range, one being the difficulty distinguishing between the two conditions because of overlapping symptoms.
ASD + ADHD Comorbidity
ASD and ADHD often co-occur, although the exact reasons are not fully understood. Current research contains theories of possible factors that may contribute to the manifestation of these conditions:
- Genetics and family history
- Similarities in brain structure
- Being male
Similarities Between the Two
While these two conditions are different, there is quite a bit of symptom overlap. Overlapping symptoms can be a sign of comorbidity, but research suggests that autistic people are more likely to have ADHD symptoms, while those who have ADHD are less likely to have ASD symptoms.
Both disorders can affect working memory, processing speed, and response inhibition. Individuals with autism may experience inattention, impaired adaptive functioning, and other cognitive and social difficulties.
Additionally, ASD and ADHD involve language delays, defiance, problems with eating or sleeping, difficulties with emotional regulation, sensory issues, and challenges with executive functioning. Both conditions are also more commonly observed in males, and symptom severity can vary significantly among individuals.
Differences Between the Two
Despite symptom overlap, ASD presents many symptoms that ADHD does not. For example, social impairment, restricted behaviors, or repetitive stimulation known as “stimming.” Children with ASD often are overfocused and have difficulty changing from one activity to another.
ADHD behaviors primarily center around impulsivity, excessive movement or talking, and difficulty concentrating or paying attention for long periods. The approach between the two is also different. Those with ADHD often respond to medication, whereas ASD relies more on behavioral therapies. Individuals with both conditions may benefit from a combination of interventions.
Identifying ASD + ADHD in Children
When evaluating children, primary consideration should be given to ADHD if the child predominantly exhibits hyperactivity, impulsivity, or inattention. ASD is most likely if the main symptoms are intense focus and interests, avoiding eye contact, delayed developmental milestones, and repetitive movements. Using tools such as the (ADOS®-2) Autism Diagnostic Observation Schedule™, Second Edition test can help identify ASD.
However, if symptoms of ASD are present, alongside other symptoms common to ADHD, such as difficulty settling down or hyperactivity, an experienced doctor can work to differentiate which symptoms may be caused by ADHD, ASD, or both conditions.
Diagnosing ASD + ADHD
Typically, when assessing for an ASD diagnosis, a clinician will need the help of an autism assessment like the(ADOS®-2) Autism Diagnostic Observation Schedule™, Second Edition test, and ADHD are diagnosed with the (CAARS) Conners’ Adult ADHD Rating Scales assessment. Often, children are diagnosed with autism before they receive an ADHD diagnosis, as the symptoms of ASD are generally more noticeable at an early age. Because of the significant overlap of traits, when testing for autism, utilize ADHD screeners, and vice versa.