ADHD, Autism, Cerebral Palsy Often Overlap

Deborah Brauser

June 19, 2012

June 19, 2012 — Diagnoses of attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), cerebral palsy, and epilepsy may often overlap in older children, new research suggests.

A new registry study of more than 700,000 children in Norway showed that by the age of 11 years, there was a significant incidence of ADHD, ASD, and epilepsy. There was also a significant proportion of cerebral palsy cases among children older than 4 years. Further, boys had a significantly higher risk for all the disorders studied than girls.

In addition, there was "considerable overlap" found between these diagnoses, including more than 17% of the children with ASD having comorbid ADHD, more than 11% of those with ASD having comorbid epilepsy, and almost 13% of those with epilepsy having comorbid cerebral palsy.

"The findings demonstrate the significant burden of disease associated with neurologic and neurodevelopmental disorders in children, and that this burden is disproportionately skewed towards boys," Pål Surén, MD, MPH, from the Center for Pediatric Epidemiology and Biostatistics at the University College London Institute of Child Health in the United Kingdom and from the Norwegian Institute of Public Health in Oslo, and colleagues write.

The investigators also note that 4.3% of the 11-year-olds registered had at least 1 of the 4 diagnoses studied.

"This is lower than recent figures from the United States, but the difference is largely driven by high prevalence rates of ADHD," they write.

The study was published online June 18 in Pediatrics.

Mandatory Registry

According to the investigators, although "numerous studies" have assessed the prevalence of these disorders individually, little research has been done to examine them collectively.

"Prevalence estimates also vary widely, which may partly be explained by the fact that most prevalence studies derive diagnoses from self-report surveys or chart abstraction, not from in-person specialist assessments," write the researchers.

They note that recent large studies have found that the prevalence rates for ASD are as high as .9% in the United States and 1.2% in the United Kingdom; the worldwide mean prevalence of ADHD is 5.3%.

The population prevalence for epilepsy in children is estimated to be between .5% and 1.0%; and the prevalence for cerebral palsy is estimated to be between .15% and .35%.

The extent of overlap between these disorders, however, has not been studied extensively, even though comorbid epilepsy has commonly been found in children with ASD, and comorbid ADHD and ASD continue to be debated.

For the current study, the investigators examined 2008-2010 data for 731,318 children from the Norwegian Patient Register (NPR), which collects mandatory information from all specialist health services in the country.

Norway currently provides free healthcare to all children up to the age of 16 years. The children selected for inclusion in this study were born from 1999 through 2010, which means they were between the ages of 0 and 11 years at the end of follow-up.

The disorders assessed were epilepsy, cerebral palsy, pervasive developmental disorder (which corresponds to ASD in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition [DSM-IV]), and hyperkinetic disorders (which corresponds to ADHD in the DSM-IV).

Extensive Overlap

Results showed that at the age of 11 years, the proportion of children with ADHD was 2.9%. The proportions were .9% for epilepsy and .7% for ASD.

In addition, the estimated cumulative incidence rates for all 3 disorders at this age were 3.4%, 1.1%, and .8%, respectively.

"The cumulative incidence is likely to be higher because some cases diagnosed before 2008 were probably missed," report the investigators.

The incidence rate of cerebral palsy for the children aged 5 years or older was .3%.

Of all the children who had a primary diagnosis of ASD, 17.3% had comorbid ADHD, and 11.2% had comorbid epilepsy. Of those having ADHD, 6.4% had comorbid ASD, and 5.3% had comorbid epilepsy.

For the children with a primary diagnosis of epilepsy, 12.8% had a comorbid diagnosis of cerebral palsy, 7.8% had comorbid ADHD, and 6.1% had comorbid ASD.

The boys had a significantly increased risk for all of the disorders studied compared with the girls.

For children between the ages of 6 and 11 years, the male/female ratio was 4.3 for ASD (95% confidence interval [CI], 3.9 - 4.9), 2.9 for ADHD (95% CI, 2.7 - 3.1), 1.3 for cerebral palsy (95% CI, 1.2 - 1.5), and 1.2 for epilepsy (95% CI, 1.1 - 1.3).

"Validation studies of these diagnoses would strengthen the research value of NPR data and will be undertaken in the years to come," write the researchers.

The study was supported by grants from the Research Council of Norway and from the National Institute of Neurologic Disorders and Stroke. The study authors have disclosed no relevant financial relationships.

Pediatrics. Published online June 18, 2012. Abstract


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