Recent Advances in the Diagnosis and Treatment of Attention-Deficit/hyperactivity Disorder in Individuals with Intellectual Disability
Huang, Haojiang, Ruedrich, Stephen, Mental Health Aspects of Developmental Disabilities
An extensive review of the literature supports that attention-deficit/hyperactivity disorder (ADHD) is a common and valid co-morbid diagnosis in individuals with intellectual disability. Two recently published diagnostic manuals, the Diagnostic Criteria-Learning Disability (DC-LD) and Diagnostic Manual--Intellectual Disability (DM-ID), support this assertion, and should improve diagnostic accuracy. However, standards are still urgently needed to establish the symptomatic thresholds, above which an individual with intellectual disability who demonstrates inattentive or hyperactive behavior, can be diagnosed as having co-morbid ADHD. Similar to neurotypical persons with ADHD, stimulants are the primary pharmacological treatment in for individuals with ADHD and intellectual disability, but expected treatment response may be less robust. Future research should attempt to refine symptomatic thresholds for ADHD diagnosis, and further characterize ADHD as a behavioral phenotype of intellectual disability etiologies.
Keywords: ADHD, behavioral phenotypes, intellectual disability, mental retardation, psychiatric, stimulants
Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioral disorder of childhood. (7) When first characterized in the early 1900s, "hyperactive syndrome" was identified in a group of impulsive, disinhibited and hyperactive children, many of whom had neurological deficits caused by encephalitis. (58) At that time, most 58 reports on ADHD focused on the motor hyperactivity seen in affected patients. Beginning in the 1970s, deficits in attention span and distractibility have supplanted motor overactivity, and they have become the defining feature of the disorder. (25)
According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostic criteria, (9) ADHD is characterized by a persistent pattern of inattention, and/or hyperactive and impulsive behavior, which are in excess of that expected for a child's development level. In their 1996 DSM-PC (The Classification of Child and Adolescent Mental Diagnoses in Primary Care: Diagnostic and Statistical Manual for Primary Care Child and Adolescent Version), the American Academy of Pediatrics offered definitions for expected and appropriate activity levels for different childhood developmental stages. (8) In the DSM-IV criteria, some of the symptoms must be present before age 7. The impairment from inattention and/or hyperactivity and impulsivity must be pervasive and clinically significant. Pervasive development disorders, psychotic disorders and other major mental disorders must be excluded before the diagnosis of ADHD can be made.
Three subtypes of ADHD are currently classified: predominantly inattentive type, predominantly hyperactive/impulsive type, and a subtype combining inattention and hyperactivity. The combined subtype is the most prevalent subgroup, accounting for 50-75% of all individuals with ADHD, followed by the inattentive subtype (20%-30%), and the hyperactive/ impulsive subtype (less than 15%). (46)
Reports on the general prevalence of ADHD vary substantially, partly due to changing conceptions of the illness and evolving diagnostic criteria over time, as well as variations in clinical assessment in different settings and with various sample populations. In the United States, it is currently estimated that the prevalence rate for ADHD in school-aged community samples is 8-10%. (7) ADHD is more prevalent in boys than girls, with the gender ratio ranging from 2-1 to as much as 9-1. (42) Most females with the disorder have been diagnosed with predominantly the inattentive subtype, which may account for a hypothesized under-diagnosis of ADHD among girls, who are less likely to demonstrate the disruptive hyperactive/impulsive behaviors seen in boys. (42)
In neurotypical samples, ADHD commonly occurs in association with oppositional defiant disorder, conduct disorder, mood disorder, anxiety disorder, and a variety of substance use disorders. …