Young Adults with ADHD: A Comparison of Combined and Inattentive Subtypes

In the current psychiatric diagnostic system, three distinct subtypes of ADHD are specified. ADHD Combined Type is used when both inattentive and hyperactive-impulsive symptoms are present. When attention problems are prominent -- and hyperactive-impulsive symptoms are not -- the diagnosis that applies is ADHD, Predominantly Inattentive Type. This is the "official" term for what people often refer to as ADD -- in contrast to ADHD. In situations where the reverse is true, the term is ADHD, Predominantly Hyperactive-Impulsive subtype. In this latter case, the term predominantly is included to reflect the fact that the individual's difficulties are predominantly in that area, although there can certainly be some difficulties with symptoms in the other area. (For information on diagnostic criteria click here.)

In order for this current method of dividing ADHD into different subtypes to be valid, there needs to be clear evidence of functional differences between individuals who have been diagnosed with the different subtypes. Several studies have found evidence of such differences among children. For example, children with the combined and hyperactive-impulsive subtypes are more likely than those with the inattentive subtype to have severe co-existing behavior disorders such as Oppositional Defiant Disorder (ODD) and Conduct Disorder (CD). In contrast, those with the inattentive subtype appear more likely to have learning difficulties and problems with academic performance.

One limitation of prior research on subtype differences is that it has been conducted almost exclusively with children. Thus, relatively little is known about subtype differences among older individuals. Beginning to examine such differences in a young adult population was the focus of a study published recently in the Journal of Nervous and Mental Disease (Murphy, K. et al (2002) Young adults with ADHD: Subtype differences in comorbidity, educational, and clinical history, 190, 147-157.)

Participants in this study included 60 individuals diagnosed with ADHD, Combined Type (ADHD-C), 36 diagnosed with ADHD, Predominantly Inattentive Type (ADHD-I), and 64 comparison subjects without ADHD. All participants were between the ages of 17 and 28. (Note: The hyperactive-impulsive subtype is relatively infrequent -- especially among older individuals -- and was not examined specifically in this study). The average age of participants was about 20, and between 15% and 30% of the participants in each group were female. Participants were recruited from consecutive referrals from clinics specializing in child and adult ADHD and had been carefully diagnosed.

Participants in the community control group were recruited through newspaper advertisements, and were excluded if they reported any history of a major psychiatric disorder or if they had a significant number of ADHD symptoms. Thus, they were not a random sample of community members because those with significant psychiatric problems were specifically excluded. This is problematic, because it means that ADHD participants are being compared to a "healthier-than-normal" comparison group. In particular, when rates of psychiatric diagnoses are examined, comparisons with the control group are not particularly informative because having a major psychiatric disorder was a specific reason for exclusion. It is also important to note that control participants did not differ in socioeconomic status from those in the two ADHD groups. Thus, the findings reported below cannot be attributed to the fact that comparison subjects were from more privileged backgrounds.

Results

Education Outcomes

Participants in both ADHD groups had significantly fewer years of education than control subjects (an average of 13 years for both ADHD groups vs. 14.3 years for the control subjects). Whereas almost 90% of control subjects were high school graduates, the graduation rates for combined and inattentive ADHD groups were 82% and 78%, respectively. Participants in both ADHD groups were also significantly less likely to be college graduates -- about 7% of participants in each group compared to almost 25% of control subjects. Participants in both ADHD groups were also significantly more likely to have received special education services.

Overall, participants with both subtypes of ADHD had clearly attained less successful educational outcomes than young adults without ADHD. The educational attainment of participants in these groups, however, did not significantly differ from each other. Thus, there was no indication that the risk of poor educational outcomes is different for individuals with the combined or inattentive subtype of ADHD.

Psychological Maladjustment

In this category, the researchers examined rates of psychiatric disorders and self-reported psychiatric symptoms among participants in the three groups. The rates of diagnosis were based on results from a structured psychiatric interview. As noted above, because control participants were excluded if they had a psychiatric disorder, comparisons with the control group are not particularly informative. Instead, the comparisons of interest here are between the two ADHD groups. Rates of psychiatric disorder for individuals with each ADHD subtype are shown below. An asterisk (*) next to the disorder indicates that the difference in rates is statistically significant. (Note: In the list below, dysthymia is the term used for a chronic, low-grade depression).

Disorder rates were consistently higher for the combined ADHD group than the inattentive group. Except for Oppositional Defiant Disorder, these differences were not statistically significant. This reflects the fact that the sample size was relatively small (it is more difficult to obtain statistically significant results with a smaller sample). A reasonable interpretation of these results is that rates of disorder among individuals with combined ADHD are greater than among those with inattentive ADHD.

Rates of self-reported psychological maladjustment were compared in the following areas: somatic complaints (i.e. aches and pains), obsessive-compulsive symptoms, depression, hostility/anger, anxiety, interpersonal sensitivity, and paranoid thinking. As expected, both ADHD groups reported significantly more difficulties in all of these areas than control participants. The combined ADHD group reported significantly more problems then the inattentive group in the areas of hostility/anger and paranoid thinking.

Antisocial, Drug, And Alcohol Histories

Rates of antisocial, drug, and alcohol-related difficulties for participants in the three groups are shown below.

Rates of arrest, self-reported drug and alcohol use, and perceptions by others of being drug- and alcohol-dependent were consistently higher among participants with ADHD. And, rates for the ADHD-C group were higher in several areas than rates for young adults with inattentive ADHD. Differences in arrest rates between the two ADHD groups were statistically significant.

History Of Mental Health Services

The final area examined was history of mental health service use. As expected, rates of psychiatric medication use were higher among the ADHD groups than control participants (34%, 14%, and 2% for ADHD-C, ADHD-I, and control subjects, respectively). Current or prior use of stimulant medication (e.g. Ritalin) was 28% for the ADHD-C participants and 13% for the ADHD-I participants. This is a striking finding and indicates that, overall, the vast majority of participants with ADHD had never been treated with medication. Thus, despite legitimate concerns about stimulant medication being inappropriately prescribed to individuals who may not need it, these findings highlight that many ADHD individuals who could legitimately benefit from medication treatment have never received it. Rates of non-medical psychiatric treatment were 52% in the ADHD-C group, 29% in the ADHD-I group, and 22% among control subjects.

Summary And Implications

The major findings from this study are that young adults with either ADHD-C or ADHD-I subtypes are likely to be experiencing multiple domains of impairment. When there are differences between the subtypes, it appears that those with ADHD-C are likely on the more negative end of the spectrum.

These findings highlight the degree to which ADHD -- when not properly treated -- can disrupt an individual's functioning beyond childhood and adolescence and into young adulthood. And, an unfortunate situation implied by these findings is just how often individuals with ADHD fail to receive appropriate treatment (recall that fewer than 25% of these young adults reported ever having received stimulant medication treatment.)

Even though medication treatment is generally recommended to be only one component of an overall treatment program, it is concerning that so few of these participants had ever received a treatment of clearly demonstrated efficacy. One can't help but wonder how many of the other difficulties experienced by young adults in this sample might have been avoided if they had been properly diagnosed and treated earlier in their lives. This is really a critical issue because, although there is currently no known cure for ADHD, the general consensus among experts is that when core ADHD symptoms are managed effectively by carefully conducted treatment, the development of other problems such as those experienced by many participants in this study can be significantly reduced.

The authors of this study emphasize that young adults with ADHD seeking clinical services are not just a reflection of the normal population "...who are overly sensitive to ordinary difficulties with inattentiveness, as skeptics of adult ADHD in the popular media have sometimes contended." Instead, these are individuals who are often struggling in multiple domains and who deserve to receive the best treatment and support available.

Note: This article originally appeared in Attention Research Update, an online newsletter written by Dr. David Rabiner, a Duke University psychologist and former member of CHADD's Professional Advisory Board. You can learn more about Attention Research Update and sign up for a free subscription at www.helpforadd.com.

Reproduced with permission of David Rabiner, Ph.D. - HelpforADD.com