Kids that have both ADHD and a lower IQ may not differ so much from kids with ADHD and a normal IQ. It appears that ADHD may affect kids with different IQ scores very similarly.
A recent study looked at the characteristics of attention deficit hyperactivity disorder (ADHD) in kids with normal intellect and kids with mild intellectual disability.
The results showed that symptoms and subtypes of ADHD and secondary disorders were very similar in both groups.
Alka Ahuja, MRCPsych, from the Institute of Psychological Medicine and Clinical Neurosciences in the UK, led a research team to investigate whether children with ADHD are clinically different if they have a mild intellectual disability.
Mild intellectual disability was defined as having an intelligence quotient (IQ) between 50 to 70 points.
According to the study authors, practitioners in the mental health community have suggested that ADHD does not occur in children with intellectual disability. But rather, any symptoms that may look like ADHD are secondary symptoms to the intellectual disability.
The study authors called this line of thought, where clinicians overlook additional psychiatric diagnoses after a child has been diagnosed with an intellectual disability, “diagnostic overshadowing.”
For this study, 971 children, between the ages of 5-17, with ADHD were recruited from 30 child and adolescent mental health clinics in the UK. Participants with any other serious psychiatric disorders or with an IQ below 50 were excluded.
The children were split into two groups based on having an IQ below or above 70 points. There were 97 children in the ADHD-intellectual disability group and 874 children in the ADHD-only group.
There were also 58 kids recruited to use as a comparison group that did not have ADHD, but did qualify for intellectual disability.
After assessment, kids with ADHD-only were:
- 85 percent male
- 73 percent had ADHD Combined type (inattentive and hyperactive-impulsive)
- 6 percent had ADHD Inattentive type
- 10 percent had ADHD Hyperactive-Impulsive type
- 46 percent had a secondary diagnosis for oppositional defiant disorder (ODD)
- 16 percent also had a secondary diagnosis for a conduct disorder (CD)
Kids with ADHD and intellectual disability were:
- 87 percent male
- 82 percent had ADHD Combined type (inattentive and hyperactive-impulsive)
- 5 percent had ADHD Inattentive type
- 6 percent had ADHD Hyperactive-Impulsive type
- 38 percent a secondary diagnosis for oppositional defiant disorder (ODD)
- 36 percent had a secondary diagnosis for a conduct disorder (CD)
The study authors concluded that the subtypes of ADHD and rates for ODD were very similar between the two groups with the exception of the rates of CD, which were 20 percent higher in the ADHD-intellectually deficient group.
There were no CD diagnoses found in the kids with intellectual deficiency but no ADHD, suggesting that intellectual deficiencies were not the driving force in CD.
“Children with ADHD and mild intellectual deficiency appear to be clinically typical of children with ADHD except for more conduct problems,” concluded the study authors.
This study was published in April in The Journal of Pediatrics.
The Baily Thomas Charitable Trust, Action Medical Research, the Welcome Trust, the UK Medical Research Council and the University of Bristol helped provide funding for this project. No conflicts of interest were declared.