Attention-Deficit Hyperactivity Disorder: Epidemiology, Causes and Diagnosis
This is the first in a series of blog posts on ADHD. In it I concisely review the epidemiology, causes and diagnosis of this condition. Future blog posts will review the effectiveness and limitations of currently available mainstream treatments of ADHD, and research findings on a variety of complementary and alternative treatments being investigated.
Epidemiology of ADHD
Attention deficit hyperactivity disorder (ADHD) occurs in children and adults with roughly equal prevalence in all countries surveyed. Surveys suggest that 7 to 8 % of children and 4 to 5% of adults fulfill criteria for ADHD. The rate at which ADHD is diagnosed and treated in both children and adults has increased dramatically since the syndrome was first recognized as a specific disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM) in the 1970s. In the United States as many as 10% of males and 4% of females have been diagnosed with ADHD. An objective epidemiological or scientific basis for the rapidly increasing prevalence of ADHD in general and the higher incidence of the syndrome in boys compared to girls is highly controversial and may reflect social issues and changes in diagnostic criteria more than actual changes in prevalence rates.
ADHD has multiple causes
The causes of ADHD are multifactorial. Data from twin studies show that ADHD is a highly heritable disorder and the risk of developing this disorder is probably influenced by genes that affect CNS transport of dopamine and serotonin. ADHD is also associated with premature birth, birth trauma, childhood illness and environmental toxins. Increased risk of ADHD is associated with in-utero exposure to alcohol, tobacco smoke and lead. As many as 20% of ADHD cases may be caused by brain injury around the time of birth. While certain food preservatives exacerbate the symptoms of ADHD, they probably do not cause the disorder. Some cases of ADHD may be associated with delayed development of certain areas of the frontal and temporal lobes and relatively rapid maturation of motor areas of the brain. Neuroimaging studies suggest that these brain regions may have relatively decreased activation in individuals diagnosed with ADHD. Children diagnosed with ADHD frequently experience disturbed sleep including restlessness, sleep walking, night terrors and restless leg syndrome; however, a causal relationship between sleep disorders and ADHD has not been clearly established. Early childhood neglect or abuse may also increase the risk of developing ADHD. Most cases of ADHD probably result from multiple genetic, developmental, physiological, environmental and psychosocial factors.
According to the DSM-5 a diagnosis of ADHD is considered to be a persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development. An ADHD diagnosis requires the presence of at least six symptoms (five for ages >17) of hyperactivity or inattention that begin before the age of 12, persist for at least 6 months, are maladaptive, inconsistent with the child’s development level, are present in tow or more settings, and are not better explained by a pre-existing medical or psychiatric disorder. Specific symptoms of inattention may include careless mistakes in schoolwork, difficulty sustaining attention in school-related tasks or play, failure to follow through with instructions, difficulty organizing tasks and activities, reluctance to engage in tasks requiring sustained attention, and being distracted easily by extraneous stimuli. Specific symptoms of hyperactivity or impulsivity may include fidgeting with hands or feet or squirming while sitting, frequently getting up in a classroom or other situation in which remaining seated is expected, running or moving in inappropriate or disruptive ways, or (in adults) subjective ‘feelings of restlessness’, difficulty engaging in quiet leisure activities and talking excessively.
Symptoms of inattention, impulsivity or hyperactivity must cause clinically significant impairment in at least two spheres including social, academic or occupational functioning. Neuropsychological testing is frequently employed to assess inattention, processing speed and neurocognitive deficits. A diagnosis of ADHD should be made in childhood only after other childhood disorders, including pervasive developmental disorders, learning disorders and anxiety disorders, have been ruled out. When evaluating adults a thorough medical history is important to rule out medical or psychiatric disorders that mimic symptoms or functional impairments that resemble ADHD. These include, for example, bipolar disorder, absence seizures, hypothyroidism, obsessive-compulsive disorder and chronic sleep deprivation.
The interested reader is referred to my ebook “Attention Deficit Hyperactivity Disorder: The Integrative Mental Health Solution” for a concise review of evidence-based non-pharmacologic approaches to this condition.