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Long-Term Outcome of Attention Deficit Hyperactivity Disorder

Introduction

Attention Deficit Hyperactivity Disorder (ADHD) probably accounts for more child psychiatric outpatients than any other single disorder. It is estimated that 3-7% of school-age children have the disorder, with much higher rates reported in some studies. The childhood syndrome primarily consists of three core symptoms, inattention (concentration difficulties, short attention span, distractibility), impulsivity (impatience, acting without thinking), and hyperactivity (restlessness, always on the go). The long-term progress or outcome of children with ADHD has drawn considerable attention, partly because of the disorder's high prevalence, and partly because a significant minority of children with ADHD become known to the criminal justice system in adolescence or young adulthood, thus constituting a major public health concern.

This article reports on the long-term outcome of children with ADHD, as shown by controlled, prospective follow-up studies into young adulthood and adulthood (i.e., late teens to mid-twenties). Since both epidemiological and clinical studies consistently have found that ADHD is more common in boys, follow-up studies have either restricted their samples to boys or have included relatively few girls. In addition, nearly all follow-up studies have been limited to white children. Therefore, the results presented in this article are based on studies of predominantly white boys with ADHD.

Early-Middle Adolescent Outcome (ages 13-15 )

Several prospective studies have followed children with ADHD into their early-mid teens. These studies fairly consistently have shown that, compared to normal controls, children with ADHD exhibit impaired academic functioning (obtain lower test scores, more often repeat grades, etc.) and perform more poorly on cognitive tasks. In addition, at follow-up, children with ADHD are more often characterized by low self-esteem and poor social functioning (e.g., described by their mothers as having no steady friends). Two-thirds to three-quarters of cases continue to meet full criteria for ADHD, and a substantial proportion (30-50% in some studies) exhibit pervasive conduct problems.

Young Adult Outcome (ages 16-19)

Follow-up studies into young adulthood have addressed outcome in four major domains, academic performance, self-esteem and social functioning, arrest history (criminality), and mental status.

Academic Performance

As noted, several short-term follow-up studies have reported academic difficulties among children with ADHD in early-middle adolescence. These difficulties persist into young adulthood. Compared to their peers, ADHD subjects complete less formal schooling, achieve lower grades, fail more courses, perform worse on standardized achievement tests, and are more likely to attend special schools.

Self-Esteem and Social Functioning

As with impaired academic functioning, low self-esteem and poor social functioning continue to characterize the child with ADHD in young adulthood. Compared to controls, children with ADHD in their late teens have fewer friends, score more poorly on tests of social skills and self-esteem, and are rated by clinicians as having poorer psychosocial adjustment.

Arrest History

Two controlled, prospective studies, one in New York (Klein & Mannuzza) and the other in Los Angeles (Satterfield), obtained the official arrest records of all subjects who resided in their state of origin during the follow-up interval. These data provide an objective index of the severity and pervasiveness of antisocial behavior that are not susceptible to the usual sources of unreliability which sometimes characterize interview data (forgetting, minimizing, denying, selective recall, etc.). Both studies found that ADHD subjects fared poorly with regard to indices of criminality. Compared to controls, these individuals showed significantly higher rates of arrests (36-58% vs. 2-20%, depending on study and social class), convictions, incarcerations (9-25% vs. 1%), multiple arrests, multiple convictions, aggressive offenses, felonies, and multiple felonies. In the New York study, the presence of an antisocial disorder (i.e., conduct disorder or antisocial personality disorder) in young adulthood almost completely accounted for the increased risk of criminality in ADHD subjects. When subjects without an antisocial disorder were compared, ADHD proband and control groups did not differ significantly, in arrest rates (28% vs. 16%). Therefore, antisocial disorder was a powerful mediating factor regarding arrest history. This finding suggests that children with ADHD are not uniformly at risk for later criminality, and only those who develop the more pervasive, antisocial syndrome are more likely to become known to the criminal justice system.

Mental Status

To date, only the New York study by Rachel Klein and Sal Mannuzza (2000) has reported the prevalence of clinical diagnoses in young adulthood. The methodology of this study will be reviewed briefly. Follow-up studies of 115 non-psychotic, cross-situationally hyperactive white children of average intelligence, who were between 6 and 12 years of age, were done after 9 years (young adult) and after 16 years (adult). All were referred by teachers because of behavior problems, and were clinically diagnosed as having hyperkinetic reaction of childhood (now called ADHD) at a child psychiatric research clinic. Children were not accepted if the primary reason for referral involved aggressive or other antisocial behaviors. Because of this exclusion criterion, we suspect that the children in the study were relatively free of conduct disorder. This is important, in view of our outcome findings regarding antisocial disorder at follow-up.

At 9-year follow-up (mean age, 18 years), 98% were evaluated. At 16-year follow-up (mean age, 25 years), 90% were assessed. A comparison group of 100 individuals with no behavior problems prior to age 13, was also recruited.

We also studied an independent, replication sample of 111 additional children with ADHD and a comparison group of 78 subjects was recruited. The results of both studies combined, are now reported.

At young adult follow-up, more than twice as many subjects as controls had an ongoing mental disorder (50% vs. 19%, p < .001). Three disorders significantly discriminated between groups: attention deficit disorder with or without hyperactivity (ADD, 37% vs. 3%), antisocial personality/conduct disorder (APD, 29% vs. 8%), and non-alcohol substance use disorder (Substance Abuse Disorder, SUD, 13% vs. 2%) which, in nearly all cases, involved marijuana. Anxiety and affective disorders were rare in both groups (1-2%).

Children with ADHD whose disorder persisted into young adulthood were at significantly increased risk for later developing APD and SUD. Specifically, 53% of subjects with persistent ADD vs. 19% of subjects with no ADD at young adult follow-up had ongoing APD or SUD. Furthermore, for those individuals who developed both APD and SUD, in all cases, onset of APD preceded (84%) or coincided with (16%) onset of SUD. These findings describe a developmental progression from ADD to APD to SUD, and underscore the significance of retaining childhood ADD symptoms in later life. Over half of the children with ADHD were still experiencing clinically significant ADHD symptoms (inattention, impulsivity, hyperactivity) at average age 18 years, and a full 27% had all three of the core symptoms. These results are consistent with those of a young adult follow-up conducted in Montreal (Weiss & Hechtman).

Adult Outcome

Prospective, controlled studies that have followed children with ADHD into adulthood have reported primarily on educational attainment, occupational history, self-esteem and social functioning, and mental status.

Educational Attainment

It is not surprising that significant deficits in educational achievement have been a consistent finding, since children with ADHD characteristically struggle in school, partly because their symptoms fare most poorly in structured settings. Compared to controls, ADHD subjects complete significantly less formal schooling, 2-3 years less, on average. One-quarter to one-third of subjects (vs. 1-9% of controls) drop out of high school. Only about 15% of subjects (vs. half of comparisons) complete a bachelor’s degree or higher. And only 3% of subjects (vs. 15-16% of controls) are enrolled in, or had completed, a graduate degree by their mid-twenties.

Occupational History

Two studies (New York and Montreal) reported that ADHD subjects had significantly lower occupational ranks than controls. This difference primarily was attributed to a greater proportion of comparisons occupying higher-level positions (e.g., lawyer, accountant, stockbroker) than ADHD subjects. Interestingly, both of these studies also found no significant difference between ADHD subjects and comparisons on rate of employment. About 90% of ADHD subjects were either gainfully employed or full-time students at mean age 25 years.

Self-Esteem and Social Functioning

Problems in self-esteem and social functioning persist into adulthood. The Montreal study administered the same self-esteem and social skills tests at young adult and adult follow-ups. ADHD subjects scored significantly worse than controls at both time periods.

Mental Status

Prospective, controlled studies (in Milwaukee, Montreal, New York, and Iowa) that have followed children with ADHD into adulthood (Barkley, Weiss & Hechtman, Klein & Mannuzza, Loney) have consistently reported that antisocial personality disorder is significantly more prevalent among ADHD subjects than comparisons at follow-up. ADHD subject rates across studies average around 26% (vs. 2-7% in comparisons).

An important question is whether conduct disorder in the initial childhood groups of subjects might account for these findings. The New York study excluded children if the primary reason for school referral involved aggressive or other antisocial behaviors. Therefore, we suspect that our sample was relatively pure with respect to ADHD and the absence of conduct disorder. In fact, other clinical data collected in childhood (e.g., parent and teacher behavior ratings) support this contention. Conversely, the other follow-up studies did not exclude these cases, and investigators of these studies have estimated relatively high rates of conduct disorders in their initial samples. Interestingly, compared to the other studies, the New York study reported the lowest rate of APD among ADHD subjects at adult follow-up (15%), although still significantly greater than among control subjects in that study (2%). Two conclusions follow. First, based on the results of the New York study (which were found in two, independent samples), childhood ADHD with or without conduct disorder is at significantly increased risk for antisocial personality disorder in adulthood. Second, as suggested by the rates of APD in other studies, childhood conduct disorder may increase risk for APD among children with ADHD even further.

The relationship between child ADHD and adult substance abuse is less clear. The New York study reported that non-alcohol substance use disorder was significantly more prevalent among ADHD subjects than comparisons (14% vs. 4%), whereas, the Milwaukee, Montreal, and Iowa studies did not.

Regarding the persistence of ADHD symptoms at mean age 25, the Montreal study found that one-third of ADHD subjects vs. 2% of comparisons reported at least one symptom as moderately or severely disabling at adult follow-up; 64% of ADHD subjects vs. 29% of comparisons were rated by psychiatrists as exhibiting restlessness during the interview. In marked contrast, the New York study reported that 7% of ADHD subjects vs. 1% of comparisons had the full or partial ADHD syndrome in adulthood. The Milwaukee study found that, when self reports were used, only 3% of ADHD subjects met full criteria for ADHD. However, this rate rose to 27% when diagnoses were based on parent reports. These widely discrepant findings are most likely due to numerous factors. For example, the Montreal study lost nearly 40% of subjects to follow-up, whereas, attrition was only 15% in the New York study. Also, different from the New York study, interviewers were not blind to group membership in either the Montreal or the Milwaukee follow-ups. In addition, as discussed in other publications, ascertainment procedures differed across studies. Furthermore, mean age at follow-up was 20 in the Milwaukee study, and 25 in the New York and Montreal studies. Finally, as demonstrated by Barkley and others, rates vary within the informant interviewed. The New York study evaluated the subjects, themselves, whereas the Montreal study queried subjects and their partners.

None of the follow-up studies showed significant differences between ADHD subjects and comparisons in the rates of anxiety or mood disorders.

Summary and Conclusions

The course of ADHD from childhood to adulthood is a bumpy road for many. In early-middle adolescence, relative deficits are seen in academic, cognitive, and social functioning, ADHD symptoms remain problematic in the overwhelming majority of these youths, and conduct problems are common.

Many of these same difficulties persist into young adulthood. As a group, these individuals continue to exhibit significant deficits in the academic and social domains. Half continue to experience disruptive or distressing symptoms of the childhood syndrome. Nearly a third fulfill criteria for an antisocial disorder, and two-thirds of these individuals become known to the criminal justice system. Drug abuse is also problematic among a significant minority of these youths.

Childhood ADHD continues to affect important functional domains in adulthood. Compared to their non-ADHD counterparts, these individuals complete fewer years of formal education, hold lower-ranking occupational positions, and continue to suffer from low self-esteem and poor social skills. In addition, they are at significantly increased risk for having an antisocial personality disorder.

There is no doubt that childhood ADHD persists into adulthood in a proportion of children with the syndrome. However, at this time, there is no stable estimate of the prevalence of "adult ADHD". Numerous differences across studies (rate of attrition, data collection procedure, type of informant, knowledge of childhood classification, age at follow-up, symptom definitions, etc.) may account for the disparate rates that have been reported.

Also, a more basic question is, What is adulthood? The New York study has been cited as showing that up to 40% of children with ADHD continue to exhibit the childhood syndrome in "adulthood". This statement is somewhat misleading since it refers to results of the young adult follow-up (mean age, 18 years), and some subjects in that study were as young as 16 when evaluated.

Also, certain estimates of "adult ADHD" in the lay press are based on the results of retrospective diagnoses, which are often unreliable, and whose validity frequently cannot be assessed, e.g., by comparing adult self-reports of childhood memories to those obtained from a knowledgeable informant such as the subject's parent. Clearly, more work is needed in this very important area to determine the risk for persistent ADHD in adulthood, given specified parameters.

Although children with ADHD, as a group, fare poorly compared to non-ADHD controls, these relative deficits do not tell the whole story. Based on the findings of the New York study, nearly all of these individuals were gainfully employed as adults, many as proprietors of successful businesses (auto repair shops, burglar alarm businesses, cookie franchises, bicycle stores, etc.). Furthermore, compared to their young adult fate, substantially fewer experienced emotional and behavioral problems as adults. Indeed, a full two-thirds of these children showed no evidence of any mental disorder in adulthood. Finally, childhood ADHD did not regularly preclude the chances of obtaining a higher-level education or profession; some attended law school and medical school, while others became accountants and stockbrokers. In conclusion, not all children with ADHD are doomed to failure.

References and Related Books

Attention-Deficit Hyperactivity Disorder
Barkley, R.A. (1998) Second Edition. New York, NY
The Guilford Press

Long-term prognosis in attention-deficit/hyperactivity disorder
Mannuzza, S. & Klein, R.G. (2000)
Child and Adolescent Psychiatric Clinics of North America, 9, 711-726

Hyperactive Children Grown Up
Weiss, G. & Hechtman, L.T. (1993), Second Edition, New York, NY
The Guilford Press