Could Atomoxetine Improve Sluggish Cognitive Tempo Symptoms?

To The Editor:

In the September 2013 issue of the journal, Wietecha et al. (2013) described their valuable clinical trial that addressed atomoxetine's effects on children and adolescents with attention-deficit/hyperactivity disorder (ADHD) and dyslexia. The results indicated that atomoxetine improved attention in the groups with ADHD or ADHD and dyslexia, not in the group with dyslexia only. Furthermore, it was the first report regarding the effect of atomoxetine on sluggish cognitive tempo (SCT). However, in Results section, we found that the group with greater improvement of ADHD symptoms had more of a score change on the Kiddie-Sluggish Cognitive Tempo (K-SCT.) This meant that it was possible that atomoxetine's effect on SCT was through the improvement of ADHD symptoms. We would like to share our concerns with respect to this point.

In Table 1 (Wietecha et al. 2013), the results showed that the score decreases for the ADHD Rating Scales (ADHD-RS) – Parent and Teacher versions were greater in subjects with ADHD and dyslexia and with ADHD only, but not in those with dyslexia only. This result indicated that atomoxetine could not benefit dyslexia itself. It is possible that the medication improved dyslexia symptoms through the improvement of ADHD symptoms. Therefore, atomoxetine was not effective for subjects with dyslexia only.

In addition, the score change for the K-SCT in those with ADHD and dyslexia were greatest, and had statistical significance. But for the group with dyslexia only, the score changes were the lowest. These results corresponded to the score changes in the ADHD-RS. As the authors stated (Wietecha et al. 2013), the change in K-SCT score showed a significant, but weak, correlation with changes in the ADHD-RS. It indicated that those with a greater score reduction in the ADHD-RS had more improvement on the K-SCT.

Based on these two points, it was suggested that although atomoxetine could not improve SCT symptoms themselves, it could benefit SCT by the improvement of ADHD symptoms. In consideration of the controversial issue between ADHD and SCT (Burns et al. 2013; Becker and Langberg 2013; Barkley 2014; Langberg et al. 2014; Saxbe and Barkley 2014) the authors needed to have conducted a statistical analysis to exclude the influence of ADHD symptoms on the K-SCT. Unfortunately, they did not do this, and did not address the issue in the Discussion section. Conducting such an analysis would produce a more reliable conclusion, and strongly power it. Otherwise, one should be careful in interpreting the results.