Attention-deficit/hyperactivity disorder (ADHD) in adults is a common-and, frequently undiagnosed-psychiatric disorder. This article will focus on the symptoms, associated features, diagnosis, differential diagnosis, prevalence, etiology and treatment of this illness. Much of the information is based on the work my colleagues and I have done over the past 20 years. Further documentation of the subjects in this article, as well as the instruments discussed, can be found in my monograph, Attention-Deficit/Hyperactivity Disorder in Adults (1995).
With no DSM-IV criteria developed for ADHD in adults, the first task is to define the symptoms of the syndrome in adults. The DSM-IV's symptomatic criteria refer to children and, not surprisingly, many of them are age-limited. In this category are such symptoms as "often runs about or climbs excessively" or "often has difficulty playing or engaging in leisure activities quietly." These specific behavioral criteria may increase interrater reliability in diagnosing childhood ADHD but they are not directly applicable to adults. Accordingly, we have had to develop tentative operational criteria. These were necessary when we began our investigations of ADHD in 1976 (before DSM-III), and we have continued to develop them because they specify characteristics more relevant to adults. Since ADHD begins in childhood, the first task is to determine the psychiatric status of the patient as a child and to make a retroactive diagnosis. Few of our patients had been evaluated or treated as children; nevertheless, one can inquire of an adult about the presence or absence of childhood DSM-IV symptoms for ADHD, but in most adults memory is cloudy, and we lack a measure of its reliability. As a screening measure we seek to obtain more global and seemingly better-remembered behavioral characterizations. To avoid the memory problem, we have employed three approaches. The best method is to speak to the patient's parents. Barring this, we have found it useful to have the parents rate their now-adult offspring as he or she had been in childhood on the Parents' Rating Scale (Wender and others 1981). This is a version of the workhorse of childhood ADHD assessment, the Conners Rating Scale. It has been standardized on normal and ADHD adults, and the score can be translated into the percentile of an adult's "hyperactivity" in childhood. The third technique is to administer a rating scale, the Wender Utah Rating Scale, in which the adult reports on his or her memories of 25 descriptors characteristic of ADHD in childhood (Ward and others 1993). This has been standardized on normal adults, adults with a major depressive disorder and adults with ADHD. The next step is to identify ADHD symptoms in the adult. The criteria that my collaborators and I have developed and employed are the Utah Criteria. The Utah Criteria makes hyperactivity in childhood continuing into adulthood a mandatory diagnostic symptom. This criterion obviously eliminates that subgroup of ADHD children and ADHD adults who were and are characterized by inattentiveness without hyperactivity and impulsivity. The more stringent requirements were employed in our research to limit our investigations to the most clear-cut subgroup of patients with ADHD. What was useful, however, for research purposes need not be helpful clinically, because it is clearly the case that many children and adults with inattention alone respond to the same treatments as do children and adults with hyperactivity and/or impulsivity. Our diagnostic criteria also eliminated patients with major mood disorders, schizophrenia, antisocial personality disorder, and schizotypal or borderline personality disorders. This was not to deny the often observed comorbidity; rather, it represented our desire to study a relatively homogeneous sample. Many individuals in these excluded categories also have prominent ADHD symptoms; and an important and as yet unexplored area is the influence of drug treatment on their ADHD symptoms. As one example, it would be of interest to determine whether the affective lability and lability of temper in patients with Cluster B personality disorders respond to the medications effective in the treatment of ADHD. Another issue (which ties in with the natural history of the disorder and will be discussed presently) is that we have observed considerable historical comorbidity for conduct disorder in our adult patients. This is a predictable finding since ADHD children are often comorbid for conduct disorder. (While there are many ADHD children without conduct disorder, most conduct-disordered children have ADHD as well.) This is important prognostically because approximately one-half of children with conduct disorder go on to develop antisocial personality disorder. Little is known about the value of drug treatment of ADHD in the presence of conduct or antisocial personality disorder. We have also encountered a continuing history of learning disorders in our adult patients. These disorders should likewise have been anticipated because ADHD children have increased comorbidity for learning disorders in reading, spelling and mathematics. These skills are rarely assessed in psychiatric evaluations of adults, and it is important to evaluate them in adults with ADHD and treat them appropriately, since learning disorders may persist through adult life.
The next question is that of the prevalence of ADHD in adults. No epidemiological studies have been conducted, but one can reach an order of magnitude calculation by estimating the prevalence of ADHD in children and the fraction of these cases that persists into adulthood. Many epidemiological studies of ADHD in childhood have been conducted. Although the diagnosis of ADHD is categorical, "yes" or "no," the categorical decision is based on the number of symptoms present. Depending on the method and the cutoffs employed, the prevalence of ADHD in childhood ranges from 3 percent to 10 percent. In all instances the disorder is found to be at least two to three times as common in boys as in girls. There is a commonly overlooked issue in determining the "true" prevalence of ADHD: the absence of a gold standard. That is, we lack the microbiological, pathological and physiological measures that are associated with medical illnesses and that permit us to accurately ascertain the sensitivity and specificity of diagnostic methods. We cannot meaningfully determine how sensitive and specific our criteria for ADHD are because we do not have any means of determining whether an individual patient "really" has the disorder. Lacking any such measure, we must make a decision to employ looser or more stringent criteria, and this is relevant to whom we treat. This question will be discussed in the context of the "pay-off matrix" in my discussion of treatment. The natural history of ADHD is optimally assessed by anterospective studies, in which children with ADHD have been followed through adolescence and into adult life. There are two such studies. Weiss and Hechtman reported on a follow-up at age 25 of "hyperactive" children they had treated when the children were 6 to 12 years old, 60 percent of whom they were able to evaluate as adults. Two-thirds of their subjects complained of at least one symptom of restlessness, distractibility or impulsivity versus 7 percent in the controls. Approximately one-half of the patients continued to have moderate or severe problems, while approximately one-quarter had developed antisocial personality disorder. Mannuzza and colleagues (1984, 1991, 1993) followed a cohort of "hyperactive" children from childhood to ages 18 and 26 and were able to obtain follow-up data from nearly all of them. At age 18, 40 percent of the patients had ADHD (compared to 3 percent of the controls), 27 percent had conduct disorder or antisocial personality disorder (versus 8 percent of the controls) and 16 percent had non-alcohol substance abuse disorder (versus 3 percent in the controls). At age 26, only 11 percent continued to have full or partial ADHD symptoms, while 18 percent had antisocial personality disorder; and the same number (16 percent) continued to have non-alcohol substance abuse disorder. The most striking feature of these studies is the relative persistence of the disorder through adolescence and its apparent decrease in early adult life. How is one to interpret the reported drop in the prevalence of ADHD between the ages of 18 and 26? One obvious answer is that the children simply outgrew the disorder. Another interpretation is that in working with the 25-year-olds, the investigators were dependent on reports by the subjects alone, while in childhood the informants had included both the subject and his or her parents. Our findings have been that adults with ADHD-having had the syndrome for their entire lives-often fail to report many of their symptoms or fail to report their severity. From a practical standpoint, we have found it necessary to include patients' spouses or "others," both in attempting an initial assessment and in determining the response to treatment. Based only on reports from the patients themselves, it is likely that these studies may have underestimated the true prevalence of ADHD. Putting the prevalence and natural history data together, it appears that one- to two-thirds of the 3 percent to 10 percent of the childhood prevalence, or somewhere between 1 percent and 6 percent of the general population, continue to manifest appreciable ADHD symptoms into adult life.
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