Over the past few decades, a consensus has emerged among psychopathologists that some patients exhibit a well-defined syndrome referred to as sluggish cognitive tempo or SCT. There are no diagnostic criteria for SCT because it has not yet been accepted as a separate disorder by the American Psychiatric Association. People with SCT are slow-moving, indolent and mentally muddled. They often appear to be lost in thoughts, daydreaming, drowsy or listless. In reviewing these symptoms and the literature, Barkley suggested that SCT be referred to as Concentration Deficit Disorder (CDD). This term is less pejorative but is not yet commonly used. Becker and colleagues recently evaluated the internal and external validity of SCT via a meta-analysis of 73 studies. Internal validity addresses the consistency of SCT symptoms as measure of an underlying construct. Based on factor analytic studies using more than 19,000 participants, the authors concluded that the items purported to measure SCT are sufficiently correlated with one another to justify the idea that they measure the same underlying construct. Further support for internal validity was found in studies reporting high test-retest and interrater reliability. As regards ADHD, the authors found that SCT correlated significantly with both inattentive (r = 0.72) and hyperactive-impulsive (r = 0.46) symptoms in adults. The greater correlation with inattentive symptoms makes sense given the nature of SCT symptoms. So these data confirm two key points about SCT: 1) it is definitely associated with ADHD symptoms and 2) it is a meaningful construct in its own right. Very little is known about the implications of SCT for the treatment of ADHD. In a naturalistic study of 88 children and adolescents with ADHD, Ludwig and colleagues examined the effect of SCT on the response of ADHD symptoms to methylphenidate. They found no significant differences in treatment response between subjects with and without SCT. McBurnett and colleagues tested the effects of atomoxetine on SCT in children with ADHD and dyslexia (ADHD+D) or dyslexia only. Atomoxetine treatment led to significant reductions in both ADHD symptoms and SCT outcomes. Because controlling for changes in ADHD symptoms did not predict changes in SCT outcomes, the authors concluded that change in SCT in response to atomoxetine is mostly independent of change in ADHD. Although these data are preliminary and in need of replication, they do provide some guidance for clinicians dealing with ADHD patients who also have SCT.
 

REFERENCE
Becker, S. P., Leopold, D. R., Burns, G. L., Jarrett, M. A., Langberg, J. M., Marshall, S. A., McBurnett, K., Waschbusch, D. A. & Willcutt, E. G. (2016). The Internal, External, and Diagnostic Validity of Sluggish Cognitive Tempo: A Meta-Analysis and Critical Review. J Am Acad Child Adolesc Psychiatry 55, 163-78.

Ludwig, H. T., Matte, B., Katz, B. & Rohde, L. A. (2009). Do sluggish cognitive tempo symptoms predict response to methylphenidate in patients with attention-deficit/hyperactivity disorder-inattentive type? J Child Adolesc Psychopharmacol 19, 461-5.

McBurnett, K., Clemow, D., Williams, D., Villodas, M., Wietecha, L. & Barkley, R. (2016). Atomoxetine-Related Change in Sluggish Cognitive Tempo Is Partially Independent of Change in Attention-Deficit/Hyperactivity Disorder Inattentive Symptoms. J Child Adolesc Psychopharmacol.

Barkley, R. A. (2014). Sluggish cognitive tempo (concentration deficit disorder?): current status, future directions, and a plea to change the name. J Abnorm Child Psychol 42, 117-25.