Response to the comments of Dr Aboul-Enein on the article 'Frequency of cognitive impairment dramatically increases during the first five years of multiple sclerosis' by Reuter et al.
Francoise Reuter, PhD,
February 10, 2011
We thank Dr Aboul-Enein for asking us to discuss in more details some results of the study published recently by Reuter et al that provides the prevalence of cognitive impairment in patients with early multiple sclerosis explored after a clinical isolated syndrome and 5 years later. This study demonstrates that the proportion of patients suffering from cognitive impairment almost doubles between baseline (29%) and five years (54%). We are surprised by the comments edited by Dr Aboul-Enein that never address the essence of our study. Nevertheless, we agree to clarify the points highlighted by the author. As noticed by the author, the population of MS patients was largely similar to the population explored in the spectroscopic study published recently in Journal of Neurology (Zaaraoui et al, J of Neurol 2010) and that aimed to assess the functional counterpart of early metabolic changes in multiple sclerosis. According to the different scientific goals of these studies, the populations of controls explored are totally different. Actually, in the study published in Journal of Neurology Neurosurgery and Psychiatry (JNNP), we included only controls that were explored in term of cognition at two time points (n=13) in order to take into account the test retest effect. In contrast, only controls that were explored in term of magnetic resonance spectroscopy were included (n=24) in the study published in Journal of Neurology. The slight variation of the prevalence of cognitive impairment at baseline in these two studies (22% versus 29%) noticed by the author is due to different controls' populations. The author has misinterpreted one result obtained in the spectroscopic study published in Journal of Neurology. Actually, the percentage of 39% represents the proportion of patients for whom the degree of cognitive impairment increased during the follow-up and not the proportion of patients suffering from cognitive impairment at five years. This approach selected for the spectroscopic study enables to assess the potential association between metabolic changes and cognitive evolution during the five-year follow-up. The author suggests that side effects related to disease modifying therapy (DMT) may significantly alter cognitive functioning. According to the small number of patients receiving DMT and the different DMT molecules prescribed, this hypothesis cannot be verified. Finally, the author has misunderstood the methodological approach used to classify each patient as cognitively preserved or impaired based on the methodology developed in the study published by Camp et al in 2005 (Camp et al, Brain 2005). Using this method, the percentage of patients with impaired cognitive functions was obtained. It is noteworthy to mention that figure 1 displays a demographic representation of the prevalence of cognitive impairment in the population and not the display of performances. We hope that we have clarified all the issues pointed out by the author.
Conflict of Interest:
Conflict of Interest