Sluggish cognitive tempo

Sluggish cognitive tempo (SCT) is a cluster of symptoms, and possibly a distinct disorder, characterized by the individual being daydreamy, mentally foggy, easily confused, and staring frequently. Individuals also have symptoms of hypoactivity, lethargy, slow movement, and even sleepiness. Children with SCT appeared to have slow processing speed and reaction times. Compared to individuals with ADHD, 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. 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 ADHD. SCT is strongly correlated with ADHD inattentive and combined subtypes. 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.

History

Symptoms of the inattentive type were first described in 1775 by Melchior Adam Weikard and in 1798 by Alexander Crichton in their medical textbooks.^[1]

Originally, SCT was thought to be a subtype of ADHD Primarily Inattentive Type (ADHD-I), however, SCT is not recognized as a mental disorder in any of the medical manuals, such as the ICD-10^[2] or the DSM-IV,^[3] neither is it part of the proposed revision of this manual, the DSM-5.^[4] SCT continues to be the subject of occasional studies in the psychological literature, particularly that involving ADHD, and focuses on how this group of individuals may differ from or be similar to those having ADHD.

SCT was originally discovered in the 1980s when the DSM-III first began subtyping ADHD as attention deficit disorder (ADD) with or without hyperactivity. Research comparing these subtypes produced a mixed pattern of results with some studies supporting the distinction while others did not.^[5] Later studies comparing these subtypes began to notice that those with ADHD-I seemed to have a higher frequency of symptoms of daydreaming, staring, being spacey or easily confused, mental fogginess, and hypoactivity or lethargy.^[6] By the late 1990s and early 2000s, studies began to appear that specifically chose participants for having these symptoms of SCT directly rather than those who met criteria for ADHD-I. Such research proved to be more fruitful in identifying a more reliable pattern of differences in cognitive abilities, comorbid disorders and impairments than had been the case for ADHD-I.^{[7][8][9][10]}

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. 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.^[11][12]

Epidemiology

Recent studies indicate that the symptoms of SCT in children form two dimensions: daydreamy-spacey and sluggish-lethargic,^[13] and that the former are more distinctive of the disorder from ADHD than the latter.^[14] This same pattern was recently found in the first study of adults with SCT by Barkley.^[15] Both of 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" (although in excited states, an SCT patient behaves very similarly to a traditional ADHD patient). Due to their drifting tendencies, those with SCT have trouble with memory retrieval. They also don't have the same risk factors and outcomes. A key behavioral characteristic of those with SCT symptoms is that they are more likely to appear to be lacking motivation. They lack energy to deal with mundane tasks and will consequently seek things that are mentally stimulating because of their underaroused state, an intense craving for emotional and intellectual stimulation. Those with SCT symptoms show a qualitatively different kind of attention deficit that is more typical of a true information input-output problem, such as memory retrieval and active working memory, and display a wavering "up and down" mental pattern with extremely variable levels of intense thought, hyperactivity, and failing memory. Conversely, those with the other two subtypes of ADHD are characteristically excessively energetic and have no difficulty processing information.^[16]

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^[15] 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."^[17]

Causes

Unlike ADHD, the general causes of SCT symptoms are unknown, though some studies of twins suggest that the condition appears to be as heritable or genetic in nature as ADHD. 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. 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. Far less is known about this group having SCT yet the impairments 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. While the 7-repeat allele polymorphism of the DRD4 gene is also linked more strongly as those with ADHD-PI group as those with ADHD/C subgroups,^[18] 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.^[19] SCT symptoms were also observed in pediatric survivors of acute lymphoblastic leukemia, where they were associated with cognitive late effects.^[20] Another study found high rates of SCT in children who had suffered prenatal alcohol exposure.^[21] However, since as much as 5% of the population may have SCT,^[22] these causes may not account for the majority of cases.

Treatment

Treatment of SCT has not been well investigated. Initial drug studies have been done only with the ADHD medication, methylphenidate (Ritalin/Concerta), and found that most children with DSM-III ADD-H (currently ADHD-C) responded well at medium-to-high doses.^[18] 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.^[23] Tests in lab rats have demonstrated that low doses of Ritalin can increase norepinephrine levels.^[24] While methylphenidate and amphetamines have many similar effects on patients (both inhibit reuptake of the neurotransmitters dopamine and norepinephrine, for example), amphetamines also promote release of those neurotransmitters; therefore, Diamond^[25] argued, amphetamines may be more helpful than methylphenidate for individuals with ADD (and/or possibly SCT). However, one study found that the presence or absence of SCT symptoms made no difference in response to methylphenidate in children with ADHD-PI.^[26] Another study, a retrospective analysis of medical histories, also found that children with SCT responded well to methylphenidate.^[27]

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.^[28]

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.

Prognosis

The prognosis of SCT is unknown. In contrast, ADHD is a developmental disorder, meaning that certain traits (inhibition, sustained attention, working memory) will be delayed in the ADHD individual. These traits can and usually do develop across time in people with ADHD, but just at a much slower rate than the average person. Even so, many people with ADHD may never reach normal levels of adult development in these areas. With ADHD, it has been estimated that this lag could be as high as thirty to forty percent. The symptoms of ADHD are often seen by the time a child enters school in nearly half of all cases. 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. 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, the 2012 study by Barkley of adults noted above 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 involve difficulties with selective attention difficulties or the capacity to distinguish important from unimportant information rapidly. 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. The comorbid psychiatric problems often associated with SCT are more often of the internalizing types, such as anxiety, depression, and social withdrawal.^[29][30] 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.^[16][31] 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.^[32]

Prevention

As the causes of SCT are largely unknown at this time, there is no known way to prevent SCT.

History of the term SCT and its relationship to the DSM

Sluggishness, drowsiness, and daydreaming were initially found to be common in children receiving the diagnosis of Attention Deficit Disorder (ADD) without Hyperactivity in the 1980s. It is unclear if the term SCT was coined by Ben Lahey and his colleagues in their study on this set of symptoms or was first used by Neeper in his dissertation with Caryn Carlson around this same time. Both identified a separate dimension or factor of inattention based on these symptoms that was distinct from that seen in ADHD. While this SCT dimension correlated more highly with the Inattention factor associated with ADHD, it was not as highly related to that of Hyperactivity-Impulsivity symptoms associated with ADHD.^[33][34][35]

In the published preliminary draft revisions 2012,^[36] APA writes that more research is needed to assess the "sluggish cognitive tempo" construct.^[37] A proposition in the DSM-5 draft's 2012 proposed a 4th category in the general ADHD diagnosis called RPI (restrictive predominantly inattentive) which would be for individuals with no more than 2 hyperactive/impulsive symptoms. This proposition would provide a descriptive name for a disorder with little or no hyperactivity, which might address the sluggish cognitive tempo construct as a clinical diagnosis and promote future research.^[38] However, the proposal was denied, as the committees did not wish to unduly increase the prevalence of psychiatric disorders in children without overwhelming evidence supporting the existence and utility of identifying a new psychiatric disorder.^{[citation needed]}

Relationship to dysexecutive syndrome

The executive system of the human brain coordinates actions and strategies for everyday 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.^[39] 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."^[40] 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 has postulated that the core cognitive deficit of those with ADHD-PI (ADD) and possibly SCT, is working memory, or, as she coined in her recent paper on the subject, "childhood-onset dysexecutive syndrome". She states:

• "Instructional methods that place heavy demands on working memory will disproportionately disadvantage individuals with ADD".
• "Language problems often co-occur with ADD, and it is suggested that part of the reason might be that linguistic tasks, especially verbal ones, tax working memory so heavily. Spatial, musical, and artistic skills, however, are often preserved or superior in individuals with ADD."
• "The working memory deficit in many children with ADD is accompanied by markedly slowed reaction times, a characteristic that covaries with poorer working memory in general."
• "Individuals with ADD have difficulty maintaining a sufficiently high level of motivation to complete a task...They go looking for something else to do or think about because they are bored...to remedy a general lower arousal level..."^[18]

However, a more recent study found that while adults with SCT had some deficits in executive functions (EF) in everyday life activities, they were primarily of 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 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.^[39]

See also

• Depersonalization disorder
• Attention-deficit hyperactivity disorder
• ADHD predominantly inattentive
• Dysthymia
• Hypothyroidism
• Bipolar II disorder
• Kleine-Levin Syndrome
• Low arousal theory
• Type B Personality

References

External links

• Dr. Barkley presents "Sluggish Cognitive Tempo vs. ADHD: Differences in Nature, Comorbidity, Impairment, and Management" at Psychiatry Grand Rounds at the Medical University of South Carolina Friday, September 7, 2012.
• "The Other Attention Disorder: Sluggish Cognitive Tempo (SCT or ADD) vs. ADHD" by Dr. Barkley (PowerPoint-Slides)