Some have attempted to answer this question by arbitrarily selecting for diagnosis a certain proportion of the population studied. For example, the
DSM-IV field study selected cutoff scores that included the 7 percent who were most impaired by ADHD symptoms, thus establishing that the remaining 93 percent of children would not be considered impaired enough to warrant diagnosis. But why should that be the cutoff for diagnosis rather than 3 percent, 10 percent, or 15 percent?
One way to address this question is to determine the percentage of individuals in the general population who typically meet diagnostic criteria for ADHD as defined by DSM-IV. The prevalence rate cited for ADHD in DSM-IV-TR is 3 to 7 percent of school-aged children. But this estimate has not been well documented in epidemiological studies. In 2001, Andrew Rowland and colleagues reported an epidemiological study that used parent and teacher reports about a population-based sample of children in North Carolina. This study found that 16 percent of the children in their sample were significantly impaired by ADHD symptoms, an incidence rate much higher than the estimate in DSM-IV. Some other studies have reported an even higher incidence of ADHD, while other researchers have found lower rates in the general population.
Whatever the incidence rate of DSM-IV-defined ADHD, how impaired are those who meet DSM-IV diagnostic criteria for ADHD in comparison to those who are just slightly below that cutoff? Lawrence Scahill and others (1999) reported a study that addressed this question. The group used a combination of parent and teacher reports to assign a large sample of children aged six to twelve years into three groups: those who fully met DSM-III-R diagnostic criteria for ADHD; a "subthreshold ADHD" group who had many symptoms, but fewer than what is usually required for diagnosis; and a non-ADHD group.
The Scahill study found that children in their subthreshold sample had less psychosocial stress—for example, less family dysfunction and less poverty and a lighter load of additional psychiatric disorders—than those who fully met diagnostic criteria for ADHD. Yet this subthreshold ADHD group still carried a burden of ADHD symptoms and, for many, additional psychiatric impairments relative to those in the non-ADHD group. Scahill concluded his report by noting that the subthreshold ADHD children, who had many ADHD symptoms but not enough to meet full di agnostic criteria, appeared to be at high risk of developing full ADHD; one-third of them already had another psychiatric disorder. I believe that such high-risk individuals, especially children, should be evaluated carefully and, if appropriate, considered for possible treatment.
A parallel might be drawn to a variety of medical problems. Individuals whose blood pressure is only slightly below the accepted cutoff for diagnosis of hypertension, or those whose blood glucose levels are just slightly below the accepted cutoff for diabetes, are generally recognized as "at risk" for problems that can easily become serious threats to health and functioning. In good medical practice, these at-risk individuals are generally provided interventions that may range from recommendations for a change of lifestyle to daily use of medication to reduce their risk to less dangerous levels.
Likewise, prescriptions for eyeglasses or contact lenses are not limited to children and adults whose vision is so impaired that they are virtually in need of a white cane. Rather, good practice usually provides corrective lenses for all those whose chronic impairments of vision interfere in any significant way with their performing the tasks of daily life. If medical practitioners employed the same pragmatic principles to guide interventions for ADHD as those used for patients with poor vision or borderline risk of hypertension or diabetes, it is likely that the number of those considered eligible for intervention would be much higher than the 3 to 7 percent estimated by the DSM-IV-TR. Yet there is still need for some threshold at or around which a clinician should be more inclined to offer diagnosis and treatment.
In its emphasis on the need for recognizing children whose ADHD impairments place them at risk of ADHD, the Scahill report called attention to the importance of early identification and intervention. As I explain in Chapter 4, some children show clear evidence of ADHD impairments from their earliest years. Parents and preschool teachers are able to recognize that this particular child is dramatically more impaired than most others of the same age in meeting the developmental challenges of his age group. In such cases, prompt evaluation is important, particularly if the child is extremely impulsive, hyperactive, or aggressive.
Severe ADHD impairments in preschool children may cause them to be at great risk of accidental injuries, rejection, and scapegoating by other children. They may also be vulnerable to emotional or physical abuse from siblings, parents, or other caretakers who are chronically frustrated by the untreated ADHD preschooler's relentless and exhausting demands. Even when a child's behavior does not cause such severe suffering, untreated ADHD in a young child can significantly hamper development of the basic skills and attitudes needed for success in the early years of school. The time for careful assessment and consideration of possible ADHD treatment of a child is that point when the impairments of ADHD are significantly interfering with that child's ability to meet age appropriate developmental challenges.
For those individuals whose ADHD impairments do not become apparent until later childhood, adolescence, or adulthood, evaluation for possible ADHD diagnosis and treatment may begin much later, but it can still lead to very important, life-transforming interventions.
I believe that the threshold for ADHD diagnosis should be one that identifies those children, adolescents, and adults who suffer from chronic developmental impairments of executive functions that significantly interfere with the tasks of daily life—and so are likely to be helped and not harmed by clinical interventions for ADHD. It is unlikely that these individuals can be adequately identified solely on the basis of counting the number of DSM-IV symptoms of ADHD that the person "often" manifests, because "often" is a subjective measure. It is also unclear what constitutes "clinically significant impairment."
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