There are a grand total of 19 studies on Sluggish Cognitive Tempo (SCT) that have been published and recorded at the National Institute of Health data base. Seventeen of those studies are somewhat
Two studies validated that the symptoms of Sluggish Cognitive Tempo include:
Slow Processing/Increased Reaction
Under Arousal and Sleepiness
Faulty Selective Memory
Several studies concluded that:
A) People with symptoms of SCT meet the classification of Predominantly Inattentive ADHD.
B) People who meet the diagnostic criteria for ADHD Inattentive do not all meet the diagnostic criteria for SCT.
Put another way, having SCT strongly predicts that you will be diagnosed with the Predominantly Inattentive subtype of ADHD (ADHD-PI) but being Predominantly Inattentive does not predict that you will have symptoms of Sluggish Cognitive Tempo.
Three studies report symptoms in individuals with Sluggish Cognitive Tempo that were not present in individuals with symptoms of Predominantly Inattentive ADHD without SCT. These symptoms included:
Higher Anxiety Levels
Higher Rates of Depression
More Social Withdrawal
Mores Social Dysfunction
Less Externalizing Behavior
One study looked at treatment with Methylphenidate (Ritalin) and found that the response to treatment was the same for Predominantly Inattentive ADHD with and without symptoms of SCT. One study found that ADHD-PI individuals with and without Sluggish Cognitive Tempo responded positively to Behavioral Therapy and that both inattentive symptoms and sluggishness symptoms were improved by the behavioral intervention.
One large study of over 2800 children found that boys with ADHD could be categorized as either:
A) Predominantly Inattentive
C) Sluggish Cognitive Tempo
This same study found that girls with ADHD could be categorized as either:
A) Predominantly Inattentive/Sluggish Cognitive Tempo
Another study found that the symptoms of Sluggish Cognitive Tempo did not predict differences in gender, age of onset of ADHD, or overlapping co morbidities.
It would appear from the first large study that girls are more likely to be inattentive and sluggish and boys less likely to be. This needs to be looked at more closely.
It should be noted that the American Psychiatric Association diagnostic manual, third edition, the DSM III had a diagnosis that was called Attention Deficit Disorder without Hyperactivity. This diagnosis was for people who were inattentive and had "inconsistent levels of orientation and alertness. They were described in the DSM III as sluggish, drowsy, and 'daydreamy'. Field trials prior to publishing the DSM IV failed to demonstrate a positive predictive value in diagnosing Predominantly Inattentive ADHD using the symptoms of SCT and these sluggishness items were discarded from the Inattentive ADHD symptom list.
Russell Barkley, a very well respected ADHD authority, believes that SCT and Predominantly Inattentive ADHD are one and the same. The psychiatric community obviously disagreed with him when they published the DSM IV. They continue to disagree with him as they are currently thinking that SCT is an entity separate from ADHD and are considering placing it in a category of its own.
Dr. Barkley has been correct about much of what he has reported about ADHD and some may argue that it does not really matter if he is right or wrong about this. SCT and ADHD-I respond about equally well to medication and behavioral therapy, both have inattention, both have fewer disruptive symptoms or externalizing symptoms when they are compared to people with ADHD Combined type or ADHD Hyperactive/Impulsive, and both are more likely to have symptoms of anxiety and depression when they are compared to the other subtypes (even though those with SCT are likely to be more anxious and more depressed).
A distinction is necessary because in people with ADHD-PI without SCT the issue of their level of arousal is significant. In people with SCT their low arousal level shades all their other symptoms. In people with SCT a treatment that addresses arousal level is imperative whereas in ADHD-PI the treatment should be tailored to address inattention without affecting arousal level.
To treat either SCT or ADHD-PI properly, the treatments must be tailored to the symptoms. A 'one size fits all' approach is not advocated in treating the three different subtypes of ADHD and a 'one size fits all' approach for Predominantly Inattentive ADHD and Sluggish Cognitive Tempo may not be appropriate either.