hyperactivity disorder: update for clinicians.

The Second Attention Disorder? Sluggish Cognitive Tempo vs. Attention-Deficit/Hyperactivity Disorder: Update for Clinicians

CATHERINE SAXBE, MD RUSSELL A. BARKLEY, PhD

Sluggish cognitive tempo (SCT) refers to an impairment of attention in hypoactive-appearing individuals that first presents in childhood. At this time, it exists only as a research entity that has yet to debut in official diagnostic taxonomies. However, it seems likely that a constellation of characteristic features of SCT may form the criteria for a newly defined childhood disorder in the foreseeable future, provided limitations in the extant findings can be addressed by future research. Most clinicians who assess and treat cases of attentiondeficit/hyperactivity disorder (ADHD) have likely seen and treated someone who falls within the parameters for SCT. This article outlines the history of SCT and reviews the current understanding of the disorder, how it is distinguishable from and similar to other attention disorders, and what future directions research and treatment may take. Based on this review and their clinical experience, the authors conjecture that SCT is probably distinct from ADHD rather than being an ADHD subtype, although there is notable overlap with the ADHD predominantly inattentive and combined presentations. (Journal of Psychiatric Practice 2014;20:38–49)

exploration of his presenting symptoms reveals significant lack of motivation and a sullen mood when frustrated, but he is largely compliant with rules and not notably or consistently defiant or oppositional. During his clinical session, he is distracted, spacey, apparently “out of touch” at times, and slouches lethargically in a chair, yet when prompted he is mostly cooperative with the interview. His insight into his parents’ concerns, however, is limited and most of his answers are brief and vague. He often looks blankly at the interviewer until questions are repeated, as if he had not attended to or fully processed them initially. Teachers have asked his parents to have him evaluated for stimulant medication because of significant attention problems in school. Completion of a Vanderbilt ADHD Rating Scale by the homeroom teacher revealed observations consistent with excessive levels of inattentive symptoms for age, but very low levels of hyperactive and impulsive symptoms, therefore consistent with ADHD-predominantly inattentive type. A Vanderbilt Scale completed by the mother corroborated the teacher’s observations of the patient’s poor attention and high distractibility, although in addition the mother endorsed more symptoms of irritability. The mother also reported that peers had begun to regard the patient as “weird” for often being the last kid to line up or comply with other instructions from the teacher.

KEY WORDS: sluggish cognitive tempo (SCT), attention-deficit/hyperactivity disorder (ADHD), children, adolescents

A 16-year-old girl was referred to the child psychiatry outpatient clinic for failing to complete tasks, freSAXBE and BARKLEY: Medical University of South Carolina, Charleston.

A 9-year-old boy is brought to an outpatient child psychiatric clinic by his parents who report that he has been getting “clipped down” in school for daydreaming, staring, poor attention, and failure to follow along with lesson plans. He has difficulty finishing homework, mainly due to sluggishness, and requires ardent prompting and nightly tutoring by his parents to complete assignments. At home, he is easily frustrated, especially with math, seems slow to process information, and exhibits a “lazy” or “bad attitude.” Further

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Copyright ©2014 Lippincott Williams & Wilkins Inc. Please send correspondence to: Catherine Saxbe, MD, Institute of Psychiatry, 2 North Youth Division, Medical University of South Carolina, 67 President’s Avenue, MSC 861, Charleston, SC 29425-8610. [email protected] Disclosure: Dr. Barkley has been a paid speaker for Eli Lilly and Shire and a paid consultant to Theravance during the previous 12 months and he receives royalties from Guilford Publications for his books, newsletter, rating scales, and videos related to ADHD. One of those rating scales for adult ADHD evaluates SCT. Dr. Saxbe has no relevant disclosures. DOI: 10.1097/01.pra.0000442718.82527.cd

Journal of Psychiatric Practice Vol. 20, No. 1

Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

SLUGGISH COGNITIVE TEMPO

quently losing items, poor focus in class, and recurrent conflicts with her mother over not doing her chores, always running late, and leaving her bedroom in perpetual disarray. The patient’s parents divorced when she was 5 years old. She has a 12-year-old sister. The patient maintains average grades (Bs and Cs) at school and has a small group of friends, but she does not participate in any extracurricular activities or hobbies other than spending hours on the computer nightly. Her mother expresses concern that her daughter may be depressed, mainly because she appears socially withdrawn, reticent, reluctant to participate in social interactions with peers, and lacks interest in activities many of her peers pursue. When she was 13 years old, the patient was evaluated by a neurologist for excessive staring spells. Several EEGs were conducted at that time to rule out possible absence seizures and showed no epileptiform activity. The patient’s report cards have consistently noted that she doodles when she should be taking notes and is rarely prepared to answer when called on by the teacher, often asking for the question to be repeated. Neither of these children was reported to be disruptive to fellow students, to be aggressive or antisocial, to be impulsive or sensation-seeking, or to be excessively talkative or hyperactive. Quite the contrary, both showed a pattern of daydreaming, a sluggish and hypoactive or even sleepy demeanor, and a propensity for withdrawn or internalizing symptoms. Both manifested types of inattentive behavior as their principal referral complaint—a form of inattention that is excessive for their age and problematic or impairing in more than one setting. Clinicians would likely posit that the impairments in attention and focus indicate a diagnosis in the ADHD “family,” and the majority of practitioners would likely be inclined to classify and treat these cases as being of the ADHD predominantly inattentive (IN) type, according to the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Revised (DSM-IV-TR)1 criteria or “presentation,” according to the DSM-52 criteria, even if criteria were not strictly met. However, research for nearly three decades has been elucidating a distinct attention disorder that may exist apart from ADHD, which has been dubbed sluggish cognitive tempo (SCT)3,4 or attention deficit disorder (ADD)5 and seems more suitable to the nature of the inattention seen in these two clinical cases.


HISTORY OF SCT VERSUS ADHD Children with the attention disturbance SCT have likely existed in the population at least throughout the past two centuries, if not longer. Descriptions of individuals with “low power” of attention or arousal, who appear to stare or daydream frequently, and to otherwise seem inattentive or sluggish and erratic in accurately processing information first appear in the medical literature in Crichton’s description of two disorders of attention in his medical textbook An Inquiry into the Nature and Origin of Mental Derangement, published in 1798.6 The first disorder he described involved distractibility, frequent shifting of attention or inconstancy, and lack of persistence or concentration, and it aligns more closely with the attention disturbance evident in ADHD. The second disorder described by Crichton involved diminished power or energy of attention that is more consonant with the attention problem evident in SCT. Crichton had little to say about the second disorder of attention other than that it may be associated with debility or torpor of the body, which weakens attention and results in individuals who are often characterized as retiring, unsocial, and having few friendships or attachments of any kind, with even those friendships seldom durable. He argued that the faculty of attention can become sufficiently weakened that it may leave an individual insensible to external objects or to impressions that would ordinarily awaken social feelings. Although resembling modern descriptions of SCT in some respects, Crichton’s characterization of this attention deficit could also be similar to the attention and social problems associated with autistic spectrum disorders or even schizoid or schizotypal personality disorders. Modern research began focusing specifically on children with SCT in 1980 as a clear consequence of the distinction made in DSM-III7 between two subtypes of ADD; those with (+H) and without (–H) hyperactivity. Barkley’s recollection of the DSM-III committee meetings was that this distinction was made largely on the basis of anecdotal reports by clinicians on the committee that such ADD children existed in their practices and needed to be identified in the official taxonomy of childhood disorders. That official distinction mistakenly assigned the impulsiveness of the disorder as being aligned with the inattentive symptoms, and so ADD–H was represented as a disorder having high levels of both inattention

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and impulsivity but low levels of hyperactive behavior. Yet despite this error, research quickly revealed that the impulsive symptoms are more closely associated with the hyperactive symptom dimension than the inattentive dimension,3,4,8 as reflected in the DSM-IV-TR1 and now the DSM-5.2 Researchers subsequently corrected this error and proceeded to conduct numerous studies comparing individuals with ADD+H and ADD–H—that is, individuals with high levels of both inattention (IN) and hyperactivityimpulsivity (HI) to those with just high IN but very low HI symptoms. Results were quite mixed and did not universally support this distinction.9,10 It appears that the first description of a subset of ADD–H children as being more drowsy, sluggish, and daydreamy than other children was in a 1985 paper by Lahey et al.,11 which described a study comparing 20 children with ADD+H to 20 with ADD–H. The authors suggested that these were two different types of attention deficits and not subtypes of the same disorder sharing the same attention disturbance. This study and other early studies in this area were nicely summarized in a 1986 review by Carlson,3 who concluded that ADD–H could be distinguished from ADD+H in its behavioral characteristics. While both groups had poor academic functioning, the peer relationship problems in ADD–H were characterized more by anxiety, shyness, and social withdrawal. Their behavior or attention problems were also better characterized as sluggish, drowsy, and apathetic. They also had lower levels of conduct problems, peer unpopularity, and social rejection. In contrast, ADD+H children were more socially rejected, displayed more aggression and conduct problems, and were not perceived as more distractible. Later reviews also reached similar conclusions.4 Thus, the concept of sluggish cognitive tempo arose to represent children with a particular pattern of high IN but low HI symptoms. Eventually, DSM-III-R12 would abolish the +H and –H types in view of the limited research supporting such subtyping, yet it called for continuing research on the ADD–H group, now termed undifferentiated ADD and placed at the end of the section on “Disorders Usually First Evident in Infancy, Childhood, and Adolescence” as a residual category without diagnostic criteria. Research would continue to explore differences between these subtypes for a few years thereafter,13 which continued to suggest a greater manifestation of SCT-like symptoms in the

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ADD–H than the +H group and possibly a reduced response to stimulant medication.14 With the advent of DSM-IV, these +H and –H subtypes reappeared in the official taxonomy as the ADHD-combined type (Ctype) and the ADHD-predominantly inattentive type (IN-type). Official sanctioning of this “subtyping” once more fostered numerous studies comparing these constructs well into the 1990s and beyond. Over the past decade, researchers have decreased their efforts to study this +H and –H (or C-type vs. Itype) distinction in favor of studying those children specifically identified with high levels of SCT symptoms in comparison to those with ADHD-C.15–20 Some studies have estimated that as many as 30%–63% of cases of the I-type have high levels of SCT.15–18,21

WHAT IS THE NATURE OF SCT VERSUS ADHD? Distinctive Symptoms There is no official diagnostic term for children whom researchers have labeled as having SCT, and hence there are no officially endorsed criteria for its clinical recognition. However, researchers have identified the most salient symptoms of SCT.15–19,21,22 These are 1) daydreaming, 2) trouble staying awake/alert, 3) mentally foggy/easily confused, 4) stares a lot, 5) spacey, mind is elsewhere, 6) lethargic, 7) under-active, 8) slow-moving/sluggish, 9) doesn’t process questions or explanations accurately, 10) drowsy/sleepy appearance, 11) apathetic/withdrawn, 12) lost in thoughts, 13) slow to complete tasks, and 14) lacks initiative/effort fades. The last two symptoms are as likely to be associated with ADHD as with SCT in children or adolescents, and so they are not recommended for assisting with differential diagnosis between these two types of attention disorders.15,22 However, the remaining twelve symptoms, among others,19 appear to be highly useful for identifying groups that may have this condition for further study. Studies evaluating the nature of SCT symptoms have routinely found that they represent separate symptom dimensions from the two traditional yet highly intercorrelated symptom dimensions that characterize ADHD (IN and HI) both in children19,22 and adults.23 Typically, at least two symptom dimensions are evident: 1) daydreamer/sleepy and 2) slow/sluggish/lethargic.15,19,22 A third symptom dimension, representing low initiation/persistence, may also be present,22 but this may be as correlated




with ADHD-IN symptoms as with SCT, thus making it less useful for case discrimination. In studies of clinic-referred and epidemiologically sampled children, these two distinct factors are evident across all of the various approaches to measurement studied to date, including parent and teacher ratings,15,18,19,22,24,25 observations of behavior at school,26 and observations of behavior in clinical settings.27 SCT symptoms demonstrate a far lower relationship to HI symptoms than they do to IN symptoms.15,18,19,21,22,25,28 In fact, the relationship of SCT to HI symptoms may become negative once the overlap of ADHD-IN with SCT is statistically removed.19 All of this is to say that the structure of SCT symptoms is not merely a reflection or broadening of the ADHD symptom dimensions as might be expected from the SCT-as-ADHD-subtype hypothesis. Instead, SCT symptoms are as independent from, or partially coupled to ADHD symptoms, as are other dimensions of psychopathology, such as depression and anxiety. Distinct Demographic Findings Very few studies to date have compared SCT and ADHD groups with regard to their parental/family demographic characteristics, which might provide further evidence of their distinctiveness. Several studies18,22 have found that SCT was not related to the age, gender, or minority status of the child. These findings were more recently replicated in a large epidemiological study by Barkley of representative samples of children15 and adults21 in the United States aged 6 to 89 years. In contrast, the Barkley study,15,21 like others, found that ADHD symptoms declined across childhood with age, were greater in boys than girls in childhood and adolescence, and were slightly but significantly associated with some ethnic groups (Hispanic-Latino) more than others. Barkley15 found that children identified with SCT were older than children identified with ADHD, implying a somewhat later age of onset for SCT symptoms. That study also found that SCT was associated with lower parental education level, lower annual household income, and a greater likelihood of a parent being out of work due to disability. Interestingly, in the survey of U.S. adults, Barkley21 found that adults classified as SCT also had less education and lower annual incomes and that, when SCT was comorbid with ADHD, those cases were more likely to be unmarried and to be out


of work on disability than were adults with ADHD alone. These initial studies of demographic differences between SCT and ADHD suggest that SCT may be more strongly associated with psychosocial adversity or stressors than is ADHD. At the very least, they imply that SCT, either as a disorder or as a symptom dimension, may have a different pattern of demographic correlates than ADHD. Neuropsychological Differences The first study of cognitive (neuropsychological) differences among attention disorders was conducted by Carlson et al.,29 who compared children with ADD+H and ADD–H. They found that both ADD groups scored significantly lower on intelligence testing. The ADD+H group had a lower full-scale IQ score than either the ADD–H or control group. Both ADD groups did poorly on tests of spelling and reading, but the ADD–H group performed more poorly on math achievement. Problems with visual matching were greater in the ADD–H then the ADD+H group, while the groups did not differ in accuracy on the inhibitory aspects of the Stroop task, in rapid naming, or on measures of receptive and expressive language, visual-motor integration, or sustained visual attention. Later research comparing the ADHD-C and the ADHD-IN types found much the same pattern—weak if any evidence of cognitive differences between these groups.30 Thus it might appear that these two disorders of attention differed less in cognitive patterns and more in ratings of disruptive behavior (higher in ADD+H), social relations (less popular but less withdrawn in ADD+H), self-esteem (lower in ADD–H), and internalizing symptoms (higher in ADD–H).4 It is noteworthy that the 1986 study by Carlson et al.29 seems to be the first report of an association of ADD–H with difficulties with math performance, a pattern that would be evident in some studies of SCT conducted much later.24 In general, there has been far less research on the neuropsychological deficits associated with SCT than has been the case with ADHD, for which the research literature is abundant.31,32 While patients with SCT may appear sluggish in their thinking, research is lacking that elucidates the precise nature of the cognitive processing deficits related specifically to this condition or that demonstrates problems with the temporality of cognitive functioning. Some studies suggest that a deficit in early information

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processing or selective attention may exist in SCT that is not characteristic of ADHD,33 but this remains to be replicated. Likewise, slower motor speed has been linked to SCT in some studies,18,34 as might be expected from its behavioral symptom profile, although this was not found in other studies.24 Skirbekk et al.20 found that variability of spatial memory performance was specifically linked to SCT but not ADHD even after controlling for IQ, ADHD inattention, and other variables. These results need to be examined in subsequent replications. A few recent studies point to the likelihood that, unlike ADHD, SCT is not as serious and pervasive a disorder of executive functioning (EF),15,21,24,28 if it is a disorder of EF at all. ADHD, for instance, is frequently associated with deficient performance on tests involving inhibition and working memory, especially nonverbal working memory,35 which is less likely to be the case, if at all, for SCT.24 Barkley15,21,36 recently used ratings of EF in daily life with large epidemiologically derived samples of children and adults and found that SCT had only very weak relationships to four of the five EF deficit dimensions (< 1% shared variance) when controlling for its association with ADHD symptoms, especially the inattention dimension. There was, however, a small but significant degree of shared variance (< 5%) between SCT and the dimension of planning and problem-solving on this scale, even after such statistical controls. However, in general ADHD-IN accounted for the vast majority of variance across most EF dimensions, with HI symptoms accounting for a lesser but still significant degree of variance, especially in the EF dimensions of self-restraint (inhibition) and emotional self-regulation. It therefore seems reasonable to conclude that SCT is not a disorder of EF while ADHD is, especially if EF is evaluated via rating scales of EF in daily life activities. Several conjectures could be advanced to account for the mild cognitive deficits linked to SCT, such as a brainstem arousal dysfunction or hypersomnia condition, given the sluggish/sleepy features evident in SCT symptoms. A more recent and compelling hypothesis is that SCT is a form of pathological mind-wandering.15,34 Both SCT and mind-wandering have been associated with daydreaming that has a negative impact on productivity in daily life. For clinicians, the important point at this time is to recognize that there is symptomatic, demographic, and neuropsychological evidence to distinguish SCT from

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ADHD, with more research ongoing to further examine and delineate the differences. Is There Overlap Between SCT and ADHD? If SCT is distinct from ADHD, the possibility exists that comorbidity between the two could exist in some cases. In Barkley’s recent national study of children in the United States, more than half (59%) of the participants who qualified as having SCT also qualified as having ADHD.15 Where an overlap existed, it was principally with ADHD-IN (22% of SCT had ADHDIN, 30% had ADHD-C) rather than with the HI-Type (8% of SCT had ADHD-HI), which is consistent with earlier studies exploring this overlap in children18–20 and adults.21 Concerning the inverse relationship, 39% of children with ADHD had SCT (31% of children with the IN Type, 27% of children with the HI Type, and 55% of children with the C-Type). While such overlap could mean that SCT is a form of ADHD, other findings seem to rule against that conclusion, such as the increased severity of impairment when both SCT and ADHD symptoms are present. Also, only 39% of the children qualifying for ADHD of any type also qualified for SCT. For instance, Barkley’s recent survey of adults in the United States21 found that 5.8% of the sample met criteria for high SCT symptoms. Approximately half (54%) of those qualifying for SCT had ADHD, yet nearly half did not. Where overlap existed, it was again principally with those subtypes of ADHD having significant IN. Similarly, approximately half of individuals qualifying for ADHD of any type (46%) also qualified for SCT. The overlap with SCT mainly involved individuals having ADHD-IN (26%) or the combined type (24%), with very few again having the HI Type (4%). This would be expected given the moderate correlation between these two symptom dimensions. It seems to us that the relationship of SCT to ADHD is one of comorbidity between two relatively distinct but related or partially coupled disorders, such as exists between anxiety and depression, and not one of subtyping within a single shared disorder. More research will help clarify if this is, in fact, the case. Distinct Patterns of Comorbidity As noted earlier, research on ADD–H compared to ADD+H found that the former was more often associated with anxiety, low self-esteem, social withdrawal,




and ratings of internalizing symptoms more generally. This was also the case in later comparisons of ADHD-IN and ADHD-C types. This pattern has carried forward to the present day comparisons of SCT vs. ADHD. More often than not, the SCT dimension has been linked more to ratings of internalizing symptoms than is the case for ADHD,16,18,19,24,25,37,38 even after controlling for the contribution of ADHD symptoms.19,22,24,37 While a few exceptions exist in this literature,28,39 the weight of the evidence supports this tighter linkage of SCT to internalizing symptoms (anxiety/depression/withdrawal) than is the case for ADHD. It also supports the conclusion of a weaker association of SCT with externalizing symptoms or disorders, such as oppositional defiant disorder (ODD), conduct disorder (CD), or psychopathy in children. ADHD, in contrast, is routinely linked to a higher risk of comorbidity for the externalizing symptom dimension generally and specifically for ODD and CD as discussed earlier and elsewhere.15,40 To our knowledge, just one study—the recent survey of U.S. children by Barkley15—has examined the relationship of SCT versus ADHD with 17 other learning, developmental, and psychiatric disorders. Both SCT and ADHD were associated with elevated rates of comorbidity for 11 of the 17 disorders as reported by parents based on diagnoses their children had received from clinicians in the past. However, SCT was not associated with higher rates of reading or math disorders, hearing impairment, or oppositional defiant, anxiety, or bipolar disorder diagnoses than the controls, while ADHD was associated with higher rates of all of these disorders except hearing impairment. Unlike ADHD, the SCT group had a higher rate of depression than either the controls or those with ADHD. Where SCT co-existed with ADHD, it was associated with higher rates of comorbidity for most disorders than was either disorder alone. These findings may help to explain the earlier findings that SCT is more strongly associated with internalizing types of symptoms than ADHD; it may be the link of SCT with depression more than with anxiety that accounts for that earlier association. In the Barkley survey of U.S. children,15 the comorbidity of SCT with ADHD created a much worse condition than was the case for either disorder alone, especially relative to the cases with SCT alone. This might suggest an additive effect of each disorder when it co-exists with the other, as if each was a distinct disorder that was associated with greater risks


when comorbid with the other. However, this pattern could also have arisen merely as a function of symptom severity. Comorbid cases had more symptoms of both disorders than was the case for the groups with each disorder alone. Distinct Domains of Impairment in Major Life Activities As discussed earlier, ADD–H (as well as its subsequent iteration, the ADHD-IN type) has routinely been associated with social withdrawal, but has been less associated with social rejection than ADHD. Children with SCT are not as socially aggressive or intrusive and consequently may be less socially impaired than those with ADHD. Studies of SCT symptoms more specifically have shown that SCT is linked to social problems generally and social withdrawal specifically.18,37,38 even in the presence of high ADHD-IN symptoms.38 Such findings may be more apparent in teacher than parent ratings.24,37 To our knowledge, Mikami and colleagues41 are the only ones who have conducted a detailed observational study of the social interactions of children with SCT. They employed a simulated chat room with children with ADHD and controls and statistically controlled for ADHD type, IQ, reading ability, and typing skill in their analyses. The study found that SCT independently predicted fewer total responses in the chat room, less perception of subtle social cues, less memory for the conversation, and a smaller proportion of hostile responses. These findings agree with the more general findings described earlier concerning the nature of SCT as involving inattention to the environment (in this case social cues) and a more socially withdrawn or at least less involved demeanor. This study may also suggest the possible role of SCT in attention and encoding dysfunction as well as a possible association with impairment in critical social behaviors of a different sort than one sees associated with ADHD (e.g., social intrusion, aggression, bossiness, excessive speech). Another domain of impairment linked to ADD–H or the later IN-type, and probably to the more specific disorder of SCT, is poor academic performance.3,4,21 ADD–H has been linked repeatedly across studies with difficulties with academic performance, and possibly specifically with problems with math, even if it is not as strongly associated with disruptive behavior in school as is ADHD. Bauermeister et al.24

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found that both SCT and ADHD-IN were each significantly and independently associated with lower academic achievement scores on testing after controlling for the other set of symptoms, whereas HI symptoms showed no such relationship to academic achievement. In addition, as noted above, SCT symptoms were uniquely associated with deficient math performance. In contrast, Becker and Langberg37 did not find an association between SCT and results of academic achievement tests after controlling for IQ and ADHD symptoms. The basis for this disparity in results is not obvious. In the recent large scale survey of U.S. children by Barkley,15,36 parents rated their child’s degree of impairment in 15 different domains of major life activities. These ratings were evaluated for their association with groups classified as ADHD only, SCT only, and ADHD + SCT, with all three groups compared with a control group. SCT cases were more impaired in all domains than control cases and had their greatest difficulties in community-leisure domains rather than home-school (work) domains. In contrast, while ADHD cases were also impaired across all domains, their greatest difficulties occurred in home-school domains. Moreover, ADHD was associated with more pervasive impairment, in that both ADHD groups (ADHD alone and combined with SCT) experienced significant impairment in at least twice as many of the 15 domains as did the SCT alone cases. Further analyses found that ADHD symptom dimensions, especially IN, contributed markedly more variance to impairment in the homeschool domains than did HI or SCT dimensions. HI, in contrast, contributed more variance to community-leisure impairments, while SCT did so to a far lesser extent. SCT was not found to be more impairing than ADHD in educational settings, at least as rated by parents. Results of Barkley’s survey of U.S. adults21 found that both the SCT only and ADHD only groups were more impaired than the control group, but that the SCT and ADHD groups did not differ in overall mean impairment. A somewhat different pattern was evident for the percentage of domains in which impairment occurred (pervasiveness). Both of the ADHD groups (ADHD alone, ADHD + SCT) were impaired in more domains than the SCT only and control groups. The SCT only group was also impaired in more domains than the group of control adults, but not to the degree evident in the ADHD groups. These

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results are consistent with numerous studies showing that individuals with ADHD experience adverse affects in many domains of major life activities relative to clinical and community control groups.42 However, the findings from the adult survey go further in suggesting that ADHD may be a more pervasively impairing disorder than SCT in most domains. Summary: How is SCT Different from ADHD? ADHD-IN and SCT symptoms are moderately intercorrelated and cases classified as having disorders on these dimensions will therefore have some shared characteristics, such as difficulty completing tasks, poorly sustained attention, poor persistence on tasks, and diminished effort. However, there are also important differences. The distractibility in SCT, when present, may be of a more internal nature, such as occurs in daydreaming and mind wandering, whereas ADHD-IN and ADHD-C are usually described as disorders involving external distraction and deficient executive functioning. As noted above, working memory and inhibitory control, as assessed by tests, have been shown to be deficient in ADHD- IN and ADHDC types but not in SCT.8,28,43 Where rating scales have been used, SCT is only minimally associated with deficits in EF, mainly with planning and problemsolving and even then only to a very small degree. In contrast, the IN dimension of ADHD accounts for the majority of variance in such deficits across all five dimensions of EF deficits in daily life.15,21 SCT seems to be chiefly associated with internalizing symptoms and related disorders (anxiety, depression, low self-esteem) more than externalizing symptoms and related disorders (ODD, CD, ADHD). It is also characterized by fewer social problems, such as unpopularity or rejection, than is the case for ADHD, although some social impairment is linked to SCT, at least as rated by teachers. This could be related to withdrawal, reticence, or shyness, as would seem to be consistent with high levels of internalizing symptoms. While both disorders are linked to problems with academic performance in school settings, the linkage of SCT to academic achievement deficits is weaker and not significant in some studies. An intriguing relationship may exist between it and deficient math achievement but this requires more research before it can be accepted as definitive. ADHD, in contrast, is linked to far greater impairment in academic performance and on achievement




tests in children, mainly due to severity of the IN dimension, though even here SCT makes some unique contribution.22 Yet the only study of adults with SCT21 found that they self-reported greater impairment in educational and work settings than was the case for adults with ADHD, so this disparity in findings likewise deserves further investigation.

IS THERE A BETTER LABEL FOR SCT? We believe that sluggish cognitive tempo is not the best term to use for this attention disorder. First, parents, patients, and clinicians may find it rather derogatory, since the term “sluggish” is associated with connotations of being retarded, slow-witted, or just plain lazy. Second, the term implies that we know the underlying core cognitive deficiency in the disorder, and this is far from the case. Studies of timing, information processing speed, or other cognitive parameters relevant to cognitive tempo have not been done with SCT cases specifically. While ADD might seem to be a more appropriate term, as suggested by Diamond,5 its use would unfortunately create confusion given that it has historically referred to what is now ADHD-IN. It would also suggest that SCT is a subtype of ADHD, a position we believe the evidence reviewed here would weigh against or at least cause one to question. While pathological mind wandering has some appeal as a basis for SCT,34 there is as yet no evidence of this. Until cognitive research on SCT is clearer and more robust in its evidence base and yields convincing evidence of the nature of a core deficit, we suggest a more general term less fraught with offense or misunderstanding. Labels such as “concentration deficit disorder,” “developmental concentration disorder,” or “focused attention disorder” might prove more generic and acceptable. These terms retain the emphasis on a problem with attention yet one that is likely distinct from ADHD but without any implication of underlying cognitive processes or disrespectful semantic baggage. More than semantics is at stake here. The nosology reflects the way we conceptualize a disorder, view our patients, and how they understand themselves.

PROBLEMS WITH THE SCT CONSTRUCT Apart from concerns about public and professional receptiveness to the label, the SCT construct is plagued by some scientific and methodological issues


that remain unresolved at this time. For instance, as noted earlier, the symptom dimensions of SCT can include anywhere from 3 to more than 20 items and may form 2 to 4 quasi-distinct underlying dimensions when statistically analyzed. It is not clear which of these numerous symptoms and dimensions are most central to the disorder and most distinguish it from ADHD or other disorders. Some research suggests it may be the cognitive (daydreamy) dimension that most distinguishes SCT from the ADHD symptom dimensions,19 but more research on this issue (e.g., sensitivity, specificity, positive and negative predictive power, and receiver operating characteristic analyses) is warranted before this conclusion can be accepted as definitive. It is also clear from this review that SCT dimensions are moderately correlated with ADHD dimensions, primarily IN, sharing 25% to 35% of their variance, arguing that they are dimensions that are just quasi-separable from ADHD and may still be a form of ADHD. While we view this as unlikely, given that the majority of the variance in SCT symptoms is not shared with ADHD symptoms, as well as the other distinguishing features identified here for SCT relative to ADHD, we concede that this issue is not yet settled in the literature. Moreover, in many of the comparisons of SCT groups with ADHD groups in recent research, SCT often appears to be associated simply with less severe deficits than ADHD, which is just as consistent with it being a milder version or subtype of ADHD as with it being a disorder distinct from ADHD. Indeed, the significant co-existence of the two disorders (35%–50% or more) found in the surveys by Barkley15,21 might serve to reinforce that view. Yet the two disorders, when combined, are much worse in their correlates and impairments than is either alone, which would not be expected if one is simply a milder version of the other. Also, the significant association of SCT with various deficits (as described earlier), after severity of ADHD symptoms was controlled for, would not occur if SCT was just mild ADHD. Moreover, a similar degree of comorbidity exists between other disorders, such as ADHD with ODD, or anxiety with depression, that does not trump the clinical or scientific utility of viewing these disorders as relatively distinct conditions. For example, adults with SCT show more impairment in the domains of work and education than adults with ADHD,21 and children with SCT show greater impairment in sports participation

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than children with ADHD.15 Support for SCT being a distinct disorder is also evident from analyses in which SCT symptoms remained uniquely predictive of certain deficits (e.g., academic and especially math performance, the EF of self-organization) even after the severity of ADHD was controlled for,15,19,21,22,24 or in which SCT appeared to have a different pattern of comorbidity.15 But such findings are currently small enough in number that SCT has not yet been definitively proven to be a unique disorder that is distinct from ADHD. Apart from the issue of SCT being a kind of ADHD, the question remains as to whether or not SCT is just another way of identifying children with, or at later risk for developing, internalizing disorders, such as anxiety or depression, given that SCT has higher levels of association with such disorders than ADHD. This issue is difficult to address conclusively given existing findings. While the Barkley survey of children15 found that SCT was associated with a higher rate of depression diagnoses (5%–10%), the vast majority of the children with SCT did not have such a diagnosis (although that does not mean they did not have the disorder given the exclusive reliance on diagnoses reported by parents in this study). In addition, while SCT is more highly correlated with internalizing symptoms than ADHD,19 SCT and the internalizing dimension still share only a small diagnostic overlap, after controlling for ADHD. Jacobson et al.22 also found that SCT remained uniquely predictive of certain types of impairment, even after depression symptoms were controlled for. These findings rule against SCT being simply a childhood presentation of the internalizing disorders of anxiety and depression.

IMPLICATIONS FOR ASSESSING SCT As with any behavioral disorder, when a patient presents with any complaint of fatigue or hypoactivity, a thorough medical evaluation, assessing especially for anemia, thyroid abnormalities, nutritional deficiencies, and sleep disorders, must be completed before considering a psychiatric diagnosis. Sluggishness coupled with poor concentration, especially if of sudden onset, necessitates blood work and possible sleep studies. At this time, SCT is not a clinically diagnosable entity because universal criteria are still being investigated. However, information from a family

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and social history carefully taken during the initial evaluation can aid in raising the suspicion for SCT, especially where complaints of inattention are mixed with those of passivity, hypoactivity, and even social withdrawal. In addition to employing rating scales of ADHD symptoms, the evaluation can be supplemented with rating scales that directly assess SCT symptoms (for adults, see Barkley 201123 and for children, see Penny et al. 200919). While the use of structured interviews is helpful in assessing for the existence of DSM disorders, such as ADHD, there are, as noted above, no official criteria yet available for SCT. Nevertheless, the U.S. survey by Barkley15 suggests that, if parents endorse at least 3 or more of the 12 symptoms of SCT discussed earlier as occurring often or more frequently, this will place a child above the 93rd percentile for the population, which is a traditional index of statistical deviance. For adults, this threshold would be 5 of the 9 symptoms studied by Barkley in his adult survey.21 When coupled with evidence of impairment in one or more major life activities, such as may be shown on normed rating scales of impairment,36,44 this would seem to be sufficient for now to rule in SCT. As mentioned previously, demographically, adult patients with SCT are more likely than populations with ADHD or control populations to be divorced21 and children with SCT are more likely to have unemployed parents, as well as parents with lower education and income.15 These findings lead naturally to various compelling hypotheses—for example, are these children daydreaming themselves to more sunny imaginings as some patients with mind-wandering describe? Or do their daily economic and intrafamilial stresses provoke intense rumination on fears and worries? In 2001, Lahey proposed that SCT might be the presentation of ADHD-IN with comorbid depression and anxiety.45 Further studies have not borne out that theory for ADHD-IN types; however it is a logical and intriguing line of reasoning when one specifically identifies cases of SCT in childhood. Certainly the sleepy, apathetic, confusedappearing child with SCT can seem—or actually be—depressed, and there is a greater correlation with depression in SCT than in ADHD.21 This area calls for more investigation. Another question is whether SCT could also represent a form of hypersomnia. Studies of sleep disturbances in individuals with SCT would seem to be indicated. Certainly an EEG study comparing chil-




dren with SCT with controls would be a meaningful investigation of possible deviations in brain wave activity. Phenotypically, children with SCT can look almost postictal at times and, while there is no evidence to date suggesting a seizure component, an important differential diagnosis for this disorder is absence or temporal lobe seizures since children with SCT have been noted to have staring spells. Is the impairment in attention a reflection of impaired consciousness?

IMPLICATIONS FOR THE TREATMENT OF SCT The most appropriate treatment for SCT is the most pressing question at the moment and necessitates further study. Stimulants (e.g., methylphenidate [MPH]), have not been shown to be particularly effective in improving the inattention and internal distraction of SCT, at least in anecdotal reports and our experience. Supportive of this experience, one study of ADHD-IN cases, many of whom had elevated symptoms of SCT, found a modest positive response to MPH, mainly at low doses, but with only 20% of cases remaining on this medication after a doubleblind, placebo-controlled trial compared to the vast majority of ADHD-C children, in whom the degree of improvement was greater.14 No large-scale medication trials have examined response to stimulants specifically in SCT, but one recent investigation shows promise for the potential use of atomoxetine. Wietecha and colleagues evaluated the treatment effects of atomoxetine compared with placebo in children 10–16 years of age in three groups: children with ADHD only, children with ADHD and dyslexia, and children with dyslexia only.46 Although a specific group with SCT was not identified, core symptoms of SCT were evaluated in all groups using the Kiddie-Sluggish Cognitive Tempo Interview Parent and Teacher subscales. SCT symptoms were assessed at baseline, 16 weeks, and 32 weeks. At 32 weeks, SCT symptoms had improved significantly with atomoxetine treatment on both subscales in all three groups. This is an exciting finding and warrants further investigation as it is the first published report to show improvement in SCT with any medication. In view of what is known about SCT, we can conjecture reasons to explore alternative medications. Given the overlap of SCT with anxiety and depression, perhaps selective serotonin reuptake inhibitors (SSRIs) might be a possible treatment. Do depressed


SCT cases present with greater impairment than non-depressed cases? Would an activating antidepressant (e.g., fluoxetine, sertraline, venlafaxine, or bupropion) reduce the observed sluggishness and boost alertness? Some clinicians have used fluvoxamine to manage pathological mind-wandering given its effects on obsessional thinking, but it is not clear that such thinking is present in SCT. Anecdotally, patients with SCT don’t themselves complain of obsessive thoughts or excessive rumination but instead of symptoms consistent with poorly regulated mind wandering. If SCT is related to hypersomnia or a disturbance of consciousness or wakefulness, then one might consider investigating the use of anti-narcoleptics, such as modafinil. The alpha-2 agonist guanfacine XR, which was recently approved for the management of ADHD, might be worth investigating for SCT, yet its side effects of sleepiness might prove counterproductive in view of the sluggish/sleepy features seen in SCT. There are many potential directions for medication trials here. With regard to psychosocial treatments, although only one study of behavior modification methods has been published, it showed that children with SCT symptoms had a good response to traditional home and school behavior management methods when targeted to their specific symptoms.47 One study of social skills training found that children with ADHD-IN type (who are more likely to have SCT) improved more in their assertive skills than did children with ADHD-C type,48 but neither type improved in other domains of social skills. Even though cognitive behavioral therapy has not been shown to be useful for ADHD,49 at least until adulthood,50 it has proven useful for children with anxiety and/or depression and might be worth trying in SCT cases given the higher than expected comorbidity between these disorders. Because so few intervention studies have been done and these trials did not study SCT specifically, there would seem to be great promise in exploring the value of various psychosocial treatments for the management of SCT specific symptoms and impairments. Given the limited evidence that treatments for ADHD cannot be automatically assumed to work similarly in cases of SCT, treatments such as cognitive-behavioral therapy or social skills training that have not proven especially useful for ADHD should be tried again in cases of SCT. In closing, we believe that SCT may represent an exciting new frontier in psychiatry and that, given

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the evidence reviewed here, SCT (with a less pejorative-sounding name) may eventually be accepted as an identifiable attention disorder with its own diagnostic criteria that distinguish it from ADHD. For that to happen, far more research needs to be done on the cognitive deficits that underlie the behavioral symptoms of SCT to answer the question, “What exactly is SCT?” We are aware of no research focusing specifically on the etiology of SCT—another direction ripe for research so as to address the question, “What causes SCT?” And given the lack of research on interventions specifically designed for SCT, an equally important issue is “What can clinicians do about it?”

12.

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15.

16.

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