Persistence of ADHD can be defined in several ways. In our assessment, we use a definition that includes not only the full diagnosis as per DSM-IV, but also those with ADHD-NOS. There is controversy in the field as to whether ADHD should be defined categorically or on a continuum. In the authors' opinion, both approaches are equally important and each one contributes to the conceptualization of the disorder. We recommend that clinicians, educators and parents attend to children with a history of ADHD who continue to have attention and impulse control problems, even when they fall short of a diagnosis. We found that fewer than half of the youth with baseline DSM-IV ADHD continued to have the full disorder one year later, but a majority of these youth had persistent disorder with a more inclusive decision rule that combines ADHD and ADHD NOS. ADHD defined more stringently at Time 1 was the strongest predictor of persistence, regardless of how persistence was defined. Furthermore, the combination of ADHD and ADHD-NOS diagnosis at wave 1 was strongly predictive of persistence at waves 2 and 3. Although full ADHD diagnosis was the strongest predictor, baseline ADHD-NOS was also a strong predictor that added information even after adjusting for full ADHD. ADHD-NOS children were 6 times more likely to have ADHD or ADHD-NOS diagnoses at follow-up. These findings are consistent with Faraone et al.'s3
conclusion, on a meta analysis of mostly clinical studies, that persistence of ADHD is greater when cases identified as presenting impairing symptoms such as ADHD in partial remission (a concept akin to ADHD-NOS) are included in the follow-up. These findings argue for considering the continuum of ADHD symptoms, even when categorical definitions are employed.
While ADHD is considered a chronic condition that theoretically should persist once diagnosed, the persistence rates obtained are lower than anticipated. To our knowledge, no other studies exist addressing this issue systematically in community samples, using DSM-IV diagnostic instruments, so comparison with similar studies is not possible. In general rates of persistence of ADHD in community samples tend to be considerably lower17,30–32
than those in clinical samples.3
Conceivably this finding is related to disorders in community samples being generally less severe (fewer symptoms and less impairment) than among subjects who seek clinical services; therefore the diagnosis of both ADHD and ADHD-NOS in community subjects is probably less stable and subject to minor fluctuations in both symptom levels or impairment. Community subjects that persist are in all likelihood those requiring services, but our previous report8
showed that few subjects with the diagnosis receive services, and among those, even fewer receive psychotropic medication which is an important component in the treatment of ADHD. Receiving medication was not an explanation for lower persistence. Paradoxically children receiving medication appear as more persistent in waves 2 and 3, implying not so much that medication was not working but that possibly that the more severe cases received treatment.
The significant interaction between ADHD-NOS and age at wave 1 suggests that persistence of ADHD-NOS is greater among older than younger children. It is possible that a subset of the older NOS cases are not diagnosed as full ADHD because DSM-IV symptom threshold or content are not appropriate to the child's age or developmental level.3
In our analyses this age interaction was better explained by cases with 6 or more inattention or hyperactivity-impulsivity symptoms with a later age of onset. It has been argued that the age of onset criterion should be revised and raised to at least 14 to 16 years.12
Presently the DSM 5 ADHD Workgroup considers changing this criterion to onset on or before 12 years. Other authors question the clinical utility and validity of the age of onset criterion.12,33
As was true in our findings, other research suggests that a sizeable proportion of those that meet symptom criteria but are classified as ADHD-NOS because their onset is after age 7, involve children with ADHD inattentive type. However, finding that 37 % of children that did not meet AOC were ADHD Hyperactive-Impulsive was unexpected given previous findings and lacks a clear explanation at present.34,35
In brief, although both research and clinical experience indicate that a lower symptom cut-off may be appropriate for older adolescents and adults, our findings lend even greater support to the argument made by clinicians and researchers alike that the onset criterion be raised to an older age regardless of the threshold.
As noted, differences in sampling, diagnostic criteria and ascertainment procedures make it difficult to compare findings across published studies. From the literature reviewed, it could not be determined whether other studies have considered context, site, or gender. Our study is the first to examine these issues and the results indicate that persistence of ADHD in children of similar ethnicity does not manifest differently across context and gender.
Psychosocial risk factors have been associated with ADHD persistence over time.5
Children in the South Bronx are exposed to more psychosocial risk factors than in Puerto Rico.18,19
However, contrary to our expectation, we did not find greater persistence of ADHD and ADHD-NOS among Puerto Rican children in the South Bronx than those in P.R.
At any time point girls were about half as likely to be diagnosed with ADHD or ADHD-NOS, however the pattern of persistence was the same for both genders. This finding is consistent with a previous community study indicating that males and females present similar risk factors and clinical profiles, including comorbidty,36
and that gender does not moderate the course of ADHD.15
Nevertheless, it is important to study the variables that may influence the likelihood of persistence or may be masking absence of gender differences in persistence.
A limitation of our study is that it can only address short-term persistence in relatively young children. The study bears replication with other populations over a longer time span. Also, direct teacher reports were not available. Our findings about school behaviors came from parents who may not have been fully cognizant of their child's behavior at school. The reliability for ADHD DISC diagnoses, as with similar diagnostic instruments, represents only fair to good agreement, and this reliability level may influence persistence findings.
Our findings however, have important implications. Persistence can be underestimated in longitudinal studies that measure and report only the full syndrome of ADHD. A subgroup of adolescents or adults that are true clinical cases but with a diagnosis of ADHD NOS may not be identified as persistent.3,37
While the diagnosis of ADHD NOS identifies cases that do not have full ADHD status, symptomatic persistence, that is, maintenance of subthreshold symptoms with impairment, is important to fully understand the progression and the outcomes of the disorder.3
Clinicians need to consider that impaired ADHD-NOS cases also need early identification and possibly treatment, given their persistence over time and potentially disabling consequences.
The DSM-IV ADHD-NOS category needs to be further studied and better operationalized in light of the current revisions considered for DSM 5 and other classification systems. Our criteria for ADHD-NOS not only qualify for the vague definition in DSM-IV, but highlight the need for more precise requirements (number of symptoms in the two dimensions and degree of impairment in two settings) that can be used to operationalize an NOS syndrome with greater specificity. Our results indicate that ADHD-NOS predict both ADHD and ADHD-NOS at follow up. This finding argues in favor of better operationalization of NOS syndromes in DSM 5, not only for ADHD but for other disorders as well.