Sluggish cognitive tempo

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Sluggish cognitive tempo (SCT) is a descriptive term for a cluster of symptoms that some researchers believe comprise a novel psychiatric disorder. Although definitions for this proposed disorder are still being developed, some mental health professionals have characterized those affected as individuals with an attention disorder which is distinct from ADHD.[1][2]

Signs and symptoms[edit]

ADHD, the only disorder of attention currently defined by the DSM-V or ICD-10, is subdivided into three types: a predominantly inattentive presentation, a predominantly hyperactive-impulsive presentation, and a combined presentation. Formal diagnosis is made by a qualified professional, and includes demonstrating six or more symptoms of inattention, hyperactivity and impulsivity, or both, for the three presentations, respectively. The symptoms must also be inappropriate, and must interfere with social, school, or work functioning, in addition to meeting multiple other diagnostic requirements.[3]

The list of symptoms used in the diagnosis of ADHD is shown below.[4]

  • Inattention symptoms: fails to give close attention to details, has trouble holding attention on tasks, does not listen when spoken to directly, does not follow through on instructions, has trouble organizing tasks, is reluctant to do tasks which require an extended mental effort, often loses things necessary for required tasks, easily distracted, forgetful in daily activities
  • Hyperactivity and impulsivity symptoms: fidgets or squirms, leaves seat inappropriately, runs or climbs inappropriately, unable to play quietly, often "on the go" or "driven by a motor", talks excessively, blurts answers early, has trouble waiting his/her turn, interrupts or intrudes on others

SCT is proposed to be a similar disorder to the predominantly inattentive presentation of ADHD, but, as discussed later, importantly distinct from it. The list of symptoms that follows is from a leading researcher of SCT, however, no universally accepted set of symptoms has been developed since this symptom cluster has not yet been recognized as an independent disorder. Additionally, requirements for a proposed diagnosis such as the number of symptoms, the duration of symptoms, and the impact on functioning are continuing to be investigated.[2]

  • Sluggish cognitive tempo symptoms: prone to daydreaming, difficulty staying awake or alert in boring situations, easily confused, easily bored, spacey or in a fog, lethargic or more tired than others, underactive or less energy than others, slow moving, don't process information as quickly or accurately as others

Dysexecutive syndrome[edit]

The executive system of the human brain provides for the cross-temporal organization of behavior towards goals and the future more generally and coordinates actions and strategies for everyday goal-directed tasks. Essentially, this system permits humans to self-regulate their behavior so as to sustain action and problem solving toward goals specifically and the future more generally.[5] Dysexecutive syndrome is defined as a "cluster of impairments generally associated with damage to the frontal lobes of the brain" which includes "difficulties with high-level tasks such as planning, organising, initiating, monitoring and adapting behaviour."[6] Such executive deficits pose serious problems for a person's ability to engage in self-regulation over time to attain their goals and anticipate and prepare for the future.

Adele Diamond postulated that the core cognitive deficit of those with ADHD-PI (ADD) is working memory, or, as she coined in her recent paper on the subject, "childhood-onset dysexecutive syndrome".[7] However, two more recent studies by Barkley[5] found that while children and adults with SCT had some deficits in executive functions (EF) in everyday life activities, they were primarily of far less magnitude and largely centered around problems with self-organization and problem-solving. Even then, analyses showed that most of the difficulties with EF deficits were the result of overlapping ADHD symptoms that may co-exist with SCT rather than being attributable to SCT itself. More research on the link of SCT to EF deficits is clearly indicated but as of this time, SCT does not seem to be as strongly associated with EF deficits as is ADHD.[5]

Causes[edit]

Unlike ADHD, the general causes of SCT symptoms are almost unknown, though one recent study of twins suggested that the condition appears to be nearly as heritable or genetically influenced in nature as ADHD.[8] That is to say that the majority of differences among individuals in these traits in the population may be due mostly to variation in their genes. The heritability of SCT symptoms in that study was only slightly lower than that for ADHD symptoms with a somewhat greater share of trait variation being due to unique environmental events. For instance, in ADHD, the genetic contribution to individual differences in ADHD traits typically averages between 75 and 80% and may even be as high as 90%+ in some studies. That for SCT may be 50-60%. Far less is known about SCT yet the symptoms seem to indicate that the posterior attention networks may be more involved in the disorder than the prefrontal cortex region of the brain and difficulties with working memory so prominent in ADHD. Unlike ADHD in which there exist hundreds of studies on molecular genetics identifying candidate genes that may contribute to the disorder, there are no studies of molecular genetics that specifically evaluated individuals having SCT.

Although ADHD appears to be linked to problems with the availability of or sensitivity to variations dopamine and norepinephrine, and/or the efficiency of the large chemical structures of the specific receptors and re-uptake receptors, the neurotransmitters that may be linked to SCT are unknown.

A recent study found a link between thyroid functioning and SCT symptoms, but effects were small and suggests that thyroid dysfunction is not the cause of SCT.[9] SCT symptoms were also observed in pediatric survivors of acute lymphoblastic leukemia, where they were associated with cognitive late effects.[10] Another study found high rates of SCT in children who had suffered prenatal alcohol exposure.[11]

Treatment[edit]

Treatment of SCT has not been well investigated. Initial drug studies were done only with the ADHD medication, methylphenidate (Ritalin/Concerta), and even then only with children who were diagnosed as ADD without hyperactivity (DSM-III) and not specifically for SCT. The research seems to have found that most children with DSM-III ADD-H (currently ADHD-C) responded well at medium-to-high doses.[7] However, a sizable percentage of children with ADD without hyperactivity (using DSM-III criteria; therefore the results may apply to SCT) did not gain much benefit from methylphenidate, and when they did benefit, it was at a much lower dose.[12] One study found that the presence or absence of SCT symptoms made no difference in response to methylphenidate in children with ADHD-PI.[13] Another study, a retrospective analysis of medical histories, also found that children with SCT responded well to methylphenidate.[14] But these studies did not specifically examine the effect of the drug on SCT symptoms. The only study of medication to date to specifically evaluate drug effects on SCT symptoms in children used atomoxetine and found it to have significant beneficial effects.[15]

Only one study has investigated the use of behavior modification methods at home and school for children with predominantly SCT symptoms and it found good success.[16]

Some SCT individuals report anecdotally that they experience improvement in their ability to focus through meditation, but this claim has not been subjected to scientific study.[citation needed]

In April 2014, The New York Times reported that sluggish cognitive tempo is the subject of pharmaceutical company clinical drug trials, including ones by Eli Lilly that proposed that one of its biggest-selling drugs, Strattera, could be prescribed to treat proposed symptoms of sluggish cognitive tempo.[17]

There is no effective treatment for SCT.[18]

Prognosis[edit]

The prognosis of SCT is unknown. In contrast, much is known about the adolescent and adult outcomes of children having ADHD.[19] Those with SCT symptoms typically show a later onset of their symptoms than do those with ADHD, perhaps by as much as a year or two later on average. They have as much or more difficulty with academic tasks and far fewer social difficulties than do people having ADHD (see population sample studies of SCT by Barkley, above). However, unlike ADHD, there are no longitudinal studies of children with SCT that can shed light on the developmental course and adolescent or adult outcomes of these individuals. Even so, a 2012 study by Barkley of adults[20] suggests that the disorder is present in the adult population and can be quite impairing in educational and occupational settings, even if it is not as pervasively impairing as ADHD in adults.

SCT is believed to possibly involve difficulties with selective attention or the capacity to distinguish important from unimportant information rapidly. Alternatively, as noted above, it may involve a pathological form of mind-wandering. In contrast, people with ADHD have more difficulties with persistence of attention and action toward goals coupled with impaired resistance to responding to distractions. Both disorders interfere significantly with academic performance but may do so by different means. SCT may be more problematic with the accuracy of the work a child does in school while ADHD may more adversely affect productivity, or the amount of work done in a particular time interval. Also, children with SCT may have difficulty with verbal retrieval from long term memory than children with ADHD. They also have a more disorganized thought process, a greater degree of sloppiness, and lose things more easily. They tend to have as high a risk for comorbid learning disabilities as do people with ADHD (23-50%). Yet there is some evidence that the type of learning disorders may differ in SCT, perhaps with a higher prevalence of math disorders than seen in those with ADHD. Instead of having greater difficulty selecting and filtering sensory input, as is in the case of SCT, people with ADHD have problems with inhibition.[21] The comorbid psychiatric problems often associated with SCT are more often of the internalizing types, such as anxiety, depression, and social withdrawal.[22][23] Their typically shy nature and slow response time has often been misinterpreted as aloofness or disinterest by others. In social group interactions, those with SCT may be ignored. Those with the other types of ADHD are more likely to be rejected in social situations, because of more intrusive or aggressive behavior. Those with classic ADHD also show externalizing problems such as substance abuse, oppositional-defiant disorder, and, to a lesser degree, conduct disorder.[24][25] One recent investigation has also found differential associations to certain personality dimensions in children: ADHD was associated with sensitivity to reward while SCT symptoms were specifically associated with punishment sensitivity.[26]

Epidemiology[edit]

Recent studies indicate that the symptoms of SCT in children form two dimensions: daydreamy-spacey and sluggish-lethargic,[27] and that the former are more distinctive of the disorder from ADHD than the latter.[28] This same pattern was recently found in the first study of adults with SCT by Barkley.[29] This has also been the case with more recent studies of college students.[30] These studies indicated that SCT is probably not a subtype of ADHD but a distinct disorder from it. Yet it is one that overlaps with ADHD in 30-50% of cases of each disorder, suggesting a pattern of comorbidity between two related disorders rather than subtypes of the same disorder.

In many ways, those who have an SCT profile have some of the opposite symptoms of those with classic ADHD: instead of being hyperactive, extroverted, obtrusive, and risk takers, those with SCT are drifting, introspective and daydreamy, and feel as if "in the fog". Due to their drifting tendencies, those with SCT may have trouble with memory retrieval. They also do not have the same risks for oppositional defiant disorder, conduct disorder, or social aggression,[24] and thus may have different life course outcomes compared to children with ADHD-PH and Combined subtypes who have far higher risks for these other "externalizing" disorders. A key behavioral characteristic of those with SCT symptoms is that they are more likely to appear to be lacking motivation and may even have an unusually higher frequency of daytime sleepiness.[31] They seem to lack energy to deal with mundane tasks and will consequently seek to concentrate on things that are mentally stimulating perhaps because of their underaroused state. Those with SCT symptoms may show a qualitatively different kind of attention deficit that is more typical of a true information input-output problem, such as poor focusing of attention on important details, erratic memory retrieval and active working memory, and possibly excessive mind-wandering.[32] Conversely, those with ADHD-PH and Combined subtypes are characteristically excessively energetic and have no difficulty processing information.[25]

Despite the apparent incompatibility between SCT and hyperactivity, and contrary to previous suggestions that SCT could distinguish a distinct group within the ADHD-PI type, Barkley's[29] study found that SCT was comorbid with ADHD-C almost as often as with ADHD-PI. According to a Norwegian study, "SCT correlated significantly with inattentiveness, regardless of the subtype of ADHD."[33]

Compared to individuals with ADHD-PH and Combined subtypes, children with SCT have far lower rates of comorbid oppositional defiant disorder and conduct disorder, a higher occurrence of anxiety symptoms, and possibly a greater occurrence of depression.[34] Most consistent across studies was a pattern of social withdrawal in interactions with peers rather than the social intrusiveness, aggressiveness, and rejection so often evident in the more well-known attention disorder, ADHD. SCT is strongly correlated with ADHD inattentive and combined subtypes.[35] However, SCT can be found in individuals who would not receive an ADHD diagnosis, and it can also be found in some individuals with ADHD hyperactivity/impulsivity. Efforts are underway to encourage researchers to use the term "concentration deficit disorder" (CDD) for SCT.[24]

In the 1990s, Weinberg and Brumback described six cases and proposed a new disorder: "primary disorder of vigilance" (PVD), which seems to be very similar to what is now called SCT.[according to whom?] Typical symptoms of it included difficulty sustaining alertness and arousal, daydreaming, difficulty focusing attention, losing one's place in activities and conversation, slow/delayed/incomplete tasks and a specific temperament and personality type among other criteria. The most detailed case report in their scientific article looks like a prototypical representation of SCT. The authors acknowledged an overlap of PVD and ADHD but argued in favor of considering PVD to be distinct in its unique cognitive impairments.[36][37] Problematic with the paper is that it dismissed ADHD as a nonexistent disorder (despite it having several thousand research studies by then) and preferred the term PVD for this SCT-like symptom complex. A further difficulty with the PVD diagnosis is that not only is it based merely on 6 cases instead of the far larger samples of SCT children used in other studies but the very term implies that science has established the underlying cognitive deficits giving rise to SCT symptoms, and this is hardly the case.[21]

History[edit]

Symptoms similar to ADHD were first systematically described in 1775 by Melchior Adam Weikard and in 1798 by Alexander Crichton in their medical textbooks. Although Weikard mainly described a single disorder of attention resembling ADHD-HI,[38] Crichton postulates an additional attention disorder, described as a "morbid diminution of its power or energy", and further explores possible "corporeal" and "mental" causes for the disorder (including "irregularities in diet, excessive evacuations, and the abuse of corporeal desires"). However, he does not further describe any symptoms of the disorder, making this an early but certainly non-specific reference to an SCT-like syndrome.[39]

In more modern times, research surrounding attention disorders has traditionally focused on hyperactive symptoms, but began to newly address inattentive symptoms in the 1970s.[40] Influenced by this research, the DSM-III (1980) allowed for the first time a diagnosis of an ADD subtype that presented without hyperactivity.[41] Researchers exploring this subtype created rating scales for children which included questions regarding symptoms such as short attention span, distractibility, drowsiness, and passivity.[40] In the mid 1980s, it was proposed that as opposed to the then accepted dichotomy of ADD with or without hyperactivity (ADD/H, ADD/noH), instead a three factor model of ADD was more appropriate, consisting of hyperactivity-impulsivity, inattention-disorganization, and slow tempo subtypes.[42]

With the publication of DSM-IV in 1994, the disorder was labeled as ADHD, and was divided into three subtypes: predominantly inattentive, predominantly hyperactive-impulsive, and combined.[43] Of the proposed SCT specific symptoms discussed while developing the DSM-IV, only "forgetfulness" was included in the symptom list for ADHD-I, and no others were mentioned.[40] However, several of the proposed SCT symptoms were included in the diagnosis of "ADHD, not otherwise specified".[43]

Prior to 2001, there were a total of four scientific journal articles specifically addressing symptoms of SCT.[40] In 2001, a researcher suggested that sluggish tempo symptoms were, in fact, adequate for the diagnosis of ADHD-I, and that their exclusion from DSM-IV was inappropriate.[44] The research article and its accompanying commentary urging the undertaking of more research on SCT spurred the publication of over 30 scientific journal articles to date which specifically address symptoms of SCT.[40]

However, in 2013, with the publication of DSM-V, ADHD continues to be classified as predominantly inattentive, predominantly hyperactive-impulsive, and combined, and there continues to be no mention of SCT as a diagnosis or a diagnosis subtype anywhere in the manual. As well, the diagnosis of "ADHD, not otherwise specified" no longer includes any mention of SCT symptoms.[3] Similarly, ICD-10, the medical diagnostic manual, has no diagnosis code for SCT.[45] Although SCT is not recognized as a disorder at this point, researchers continue to debate its usefulness as a construct and its implications for further attention disorder research.[40]

Controversy[edit]

Significant skepticism has been raised within the medical and scientific communities as to whether SCT, currently considered a "symptom cluster," actually exists as a distinct disorder.[17]

Dr. Allen Frances, an emeritus professor of psychiatry at Duke University, has commented "We're seeing a fad in evolution: Just as ADHD has been the diagnosis du jour for 15 years or so, this is the beginning of another. This is a public health experiment on millions of kids...I have no doubt there are kids who meet the criteria for this thing, but nothing is more irrelevant. The enthusiasts here are thinking of missed patients. What about the mislabeled kids who are called patients when there’s nothing wrong with them? They are not considering what is happening in the real world."[17]

UCLA researcher and Journal of Abnormal Child Psychology editorial board member Steve S. Lee has also expressed concern based on SCT's close relationship to ADHD, cautioning that a pattern of over-diagnosis of the latter has "already grown to encompass too many children with common youthful behavior, or whose problems are derived not from a neurological disorder but from inadequate sleep, a different learning disability or other sources." Lee states, "The scientist part of me says we need to pursue knowledge, but we know that people will start saying their kids have [sluggish cognitive tempo], and doctors will start diagnosing it and prescribing for it long before we know whether it’s real...ADHD has become a public health, societal question, and it’s a fair question to ask of SCT."[17]

Adding to the controversy are potential conflicts of interest among the condition's proponents, including the funding of prominent SCT researchers' work by the global pharmaceutical company Eli Lilly[17] and, in the case of Dr. Russell Barkley, a leader in the burgeoning SCT research field, direct financial ties to that company (Dr. Barkley has received $118,000 from 2009 to 2012 for consulting and speaking engagements from Eli Lilly).[46] When referring to the "increasing clinical referrals occurring now and more rapidly in the near future driven by increased awareness of the general public in SCT", Dr. Barkley writes "The fact that SCT is not recognized as yet in any official taxonomy of psychiatric disorders will not alter this circumstance given the growing presence of information on SCT at various widely visited internet sites such as YouTube and Wikipedia, among others."[47]

See also[edit]

References[edit]

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