Although the significance of attentional difficulties for learning and behavior was recognized in the 19th century, clinical interest in attention deficit hyperactivity disorder (ADHD) is a relatively modern phenomenon. Still’s work (1) raised some of the important issues that are still of concern today, e.g., the relative importance of environmental over "organic" factors and the primacy of attentional factors. During the 1920s, the awareness of behavioral difficulties following the influenza pandemic emphasized the importance of organic factors in pathogenesis and entwined the notion of "brain damage" with the diagnostic concept of "minimal brain dysfunction" (2). This term was unsatisfactory in many respects, and in DSM-II the term hyper kinetic reaction of childhood was adopted. Subsequent efforts were made to disentangle attentional, behavioral, and learning problems. In DSM–III, the concept was termed attention deficit disorder (with and without hyperactivity). The shifting debate about the primacy of attentional factors over hyperactivity was resolved in DSM-III-R by discarding the concept of ADD without hyperactivity. DSM-IV allows for distinction depending on whether either hyperactivity or inattention predominates or if both symptom clusters are present (3). These various diagnostic changes have had a major impact on research as well as on epidemiology, e.g., changes in DSM-IV increased the prevalence of the disorder (3, 4) and treatment. Recent research has also raised critical questions about the disorder, e.g., relative to basic mechanisms, genetic vulnerabilities, and course. Two papers in this issue of the Journal provide important perspectives on this condition.
Olfson and colleagues report on national trends in the outpatient treatment of ADHD in children. Using service utilization data from two nationally representative samples, from 1987 and 1997 respectively, trends in treatment were analyzed relative to age, gender, race, family income, and health insurance status. The authors used statistical controls for secular changes in patient features, and their data show a threefold increase in the rate of outpatient treatment between 1987 and 1997, with significant increases in ranges across almost all groups and with particularly large increases among children from more impoverished families. Somewhat paradoxically, as stimulant utilization increased, there was also a significant decrease in the number of treatment visits. This suggests that the nature of the clinical visits changed over time, likely with a greater focus on medication management.
As Olfson and colleagues note, the 1997 estimates they obtained are similar to rates obtained in other epidemiological studies in preschool children. What factors are responsible for the increased rates? As mentioned in the report, several factors are likely involved, including increased recognition of the disorder on the part of teachers and parents as well as health care providers. Changes in treatment over time in relation to family income are also cited. In 1987, children from lower-income families were less likely to be treated, while in 1997 rates of treatment were not strongly related to family income.
A number of different factors appear to be responsible for the tremendous variability in the estimated prevalence rates of the disorder—from 2% to 17% in one review of 19 studies (5). These include changes in definition in DSM-IV, methods of sampling and data collection, and choice of informant. Inclusion of three subtypes in DSM-IV increases the prevalence of the condition (3). Issues of syndrome thresholds clearly have a major impact on case definition, and it is clear that important problems, e.g., the pervasiveness of symptoms over settings, the degree of distress or impairment exhibited, and the persistence of disability over development need to be addressed (6). These issues call for a careful reappraisal of the current "epidemic" of ADHD in this country.
Various factors may explain the paradoxical trends for fewer treatment visits with greater medication usage, but this issue remains an open one in need of additional research. Changes in the type of service provided may account for some of this change. The lack of access to treatment for uninsured children remains an important public health concern. This issue is not unrelated to the epidemiological one, since in the real world, a limited pool of funds are available—even for insured children—and increasing diagnosis of the condition can result in diminishing services. The recent Surgeon General’s report (7) underscored the major difficulties in access to care for children with serious psychiatric disorders; this issue becomes even more important in relation to preventing ultimate disability and fostering academic and occupational success. It should also be noted that the recent NIMH-sponsored Multimodal Treatment Study of ADHD showed medication in a research center was significantly better than management in the community (8).
As children with attentional difficulties are followed over time, it has become clear that these problems can be quite persistent and associated with a range of difficulties in adulthood (9). Research with adults with ADHD has the potential for elucidating mechanisms that may account for persistence of the disorder. In their article in this issue, Ernst and colleagues focus on neural substrates of decision making in adults with ADHD. PET techniques were used in a task in which short-term benefit was weighed against longer-term loss. Differences were found in brain regions activated during the decision-making task, suggesting that the neural circuits underlying decision making differ in adults with ADHD. As the authors note, this observation may also have implications for developing new treatment strategies. Although minimal brain dysfunction has long been discarded as a diagnostic term, this study reminds us of the importance of brain mechanisms in understanding clinical disorder.
Both of these studies featured in this issue are a testament to the increased sophistication of research on ADHD. Many important questions remain to be answered, e.g., implications of diagnostic subtypes and, potentially, underlying neural mechanisms to treatment. The increasing diagnosis of the condition—in children, adolescents, and adults—raises important questions. The implications of long-term treatment for the condition and disentangling the complex question of comorbidity and ADHD remain important research issues as well. In conclusion, although DSM-IV opens the door to increased prevalence of ADHD, we must also be concerned about missing cases in schools and primary care settings. Moreover, even when ADHD is recognized, children may not get appropriate treatment because of problems of access to services or difficulites in dissemination of best practices.
Address reprint requests to Dr. Fred R. Volkmar, M.D., Yale University Child Study Center, 230 South Frontage Rd., New Haven, CT 06520; email@example.com (email).