1. Introduction
Conventional MRI sequences continue to be the mainstay in the diagnosis and monitoring of multiple sclerosis (MS) patients. However, they mainly assess the inflammatory processes of MS and therefore its correlation with clinical outcomes is only partial (Filipp & Grossman, 2002; Li et al., 2006; Fisniku et al., 2008; Enzinger et al., 2001; Rudick et al., 2006; Minneboo et al., 2009). Brain volumes analysis allow the evaluation of its neurodegenerative mechanisms. There is a robust evidence linking brain atrophy with disability in MS (Kearney et al., 2014; Popescu et al., 2013; Pérez-Miralles et al.,2015; Deloire et al., 2011; Benedict et al., 2013; Calabrese et al., 2011; Azevedo et al., 2015; Rocca et al., 2017; Vollmer et al., 2016; Vidal-Jordana et al., 2018), and the incorporation of these techniques into the routine daily basis could be of great value to improve the follow-up of this disease. Nonetheless there are still many methodological and biological factors that generate an important variability in their results, and hold back its use to research projects (Sastre-Garriga et al., 2017). The objective of this study is to analyze the relationship between advanced MRI sequences and physical disability and cognitive functioning in MS patients in a clinical practice setting in order to increase our knowledge of these techniques and move forward its implementation as another routine evaluation tool. 

2. Materials and Methods 
This research is a cross-sectional study. We included MS patients according the McDonald 2010 criteria (Polman et al., 2011) attending the demyelinating diseases unit at Torrejon University Hospital, Madrid, between December/2015 and December/2016. The patients gave their informed consent. The study complied with the Helsinki declaration and the results are completely confidential according to the personal data protection law (1999). 
Clinical and epidemiological data were obtained retrospectively through review of the medical charts. Cognitive functioning was evaluated with the Brief Repeatable Battery of Neuropsychological Tests (BRB-N) (Rao et al., 1991), which consists of the Selective Reminding Test (verbal memory), the Paced Auditory Serial Adittion Test (PASAT) (working memory), verbal fluency test and Symbol Digit Modalities Test (SDMT) (executive functions and speed processing) and Spatial Recall Test (SPART) (visual memory). The results were adjusted to age, sex and education level for the Spanish population (Duque et al., 2012). We also obtained the Beck Depression Inventory-II (BDI-II) (Sacco et al., 2016)and the Multiple Sclerosis Fatigue Scale (Fisk et al., 1994; Casanova et al., 2000). Advanced MRI evaluation was done by Icometrix® software through T1-3D and FLAIR-3D sequences. We analyzed whole brain volume (WBV), Gray Matter Volume (GMV) and T2 lesion load (T2). We defined cognitive dysfunction for a cognitive domain as a score lower than 1.5 standard deviations in its neuropsychological test. The association between brain volume measurements and clinical variables was studied with lineal multivariate regression, and between brain volumetry and number of affected cognitive domains with negative binomial regression. Statistical analysis was done with SPSS software, version 19. Statistical significance was set at p<0.05. 

3. Results
A total of 41 patients were studied, including 31 relapsing-remitting MS (RRMS), 6 secondary progressive MS (SPMS), and 4 primary progressive MS (PPMS). 27 samples were women. Mean age was 43.85±11.1 years, and mean duration of MS was 8±1.09 years. Mean score of EDSS was 2.6±1.9 and median EDSS 2 (Intercuartile range (IQR): 1.0-4.0). Average education level was 11.5±3.3 years. Mean score of BDI-II was 12.2±9.0, and mean score of MSFS was 9.4±8.9 (Table 1). 

Average number of affected cognitive domains was 0.83±6.3. 25 patients (61%) obtained normal punctuations in all the tests. 7 patients had impairment in 1 cognitive domain, and 9 patients (22%) had two or more (Table 2).

The most frequent affected cognitive domain was working memory (29.3%), followed by speed processing (17.1%) and verbal memory (12.2%) (Table 3). 

Multivariate regression analysis found a relationship between WBV and age (b= -2.4, p=0.037), GMV with age (b=-1.7, p=0.014) and EDSS (b=-7.55; p=0.013), and finally T2L with EDSS (b=2.29; p=0.032).
Negative binomial regression analysis revealed an association between cognitive dysfunction and clinical phenotype (greater dysfunction in PPMS) (OR RRMS/PPMS 0.037, p=0.016; OR SPMS/PPMS 0.02, p=0.028), but not with MRI data (WBV p=0.383; GMV p=0.495; T2L p=0.451). 

4. Discussion
In our study we obtained a proportion of cognitive dysfunction (impairment in 2 or more cognitive domains) of 22%, lower than other published series, normally ranging 40-60%. This difference could be explained to the composition of our sample with a predominance of RRMS, which is associated with a lesser cognitive damage (Chiaravalloti & DeLuca, 2008; Denney et al., 2005; Ruano et al., 2017), and low disability (global mean EDSS: 2.6, and mean EDSS in the RRMS group of 1.8). Nonetheless, cognitive impairment can be present even in early phases of the disease, and in patients with a good clinical situation (Migliore et al., 2017; Amato et al., 2001; Hankomäki et al., 2014), so the differences between different samples must be related to other factors not completely understood. 
Regarding the affected cognitive domains we obtained similar results to other studies, with more repercussion in executive functions, speed processing and verbal memory (Rao, 1995; Benedict et al., 2002), although we also got a lower percentage of dysfunction of these domains compared to other studies. 
When we analyzed the relationship between volumetry measurements and cognitive status we only obtained an association with the clinical phenotype. This result is in line with previous works, in which cognitive dysfunction is more frequent and more intense among progressive forms of the disease (Chiaravalloti & DeLuca, 2008; Denney et al., 2005; Ruano et al., 2017). In our study it is noteworthy the lack of association between cognitive impairment and advanced MRI sequences (WBV and GMV). In spite of the differences in the methodologies of different studies, most of them find correlations between brain volumes and physical and cognitive functioning (Rocca et al., 2017; Vollmer et al., 2016). In our study is especially striking for the GMV which is one of the brain volume measurements with a greater impact in the disability in MS (Steenwijk et al., 2016; Filippi et al., 2013; Fisher et al., 2008; Rudick et al., 2009). Again, these differences could be justified by methodological reasons, regarding the design of the study (cross-sectional instead of longitudinal), the characteristics of our sample (low frequency of cognitive impairment), as well as technical factors related to the acquisition and analysis of the images (Eshaghi et al., 2018).
Multivariate regression showed a significant relationship between EDSS and GMV and T2L. In this regard there is also a great variability among different studies, but most of them find a positive association between these data, especially with the atrophy of the gray matter (Eshaghi et al., 2018), and even with composite measurements of GMV-T2L (Moodie et al., 2012; Gauthier et al., 2007). At last, we also found a correlation between age and a loss of cerebral volume, both global and gray matter. This result could be expected as brain volume decrease physiologically with age and with a longer duration of the disease. 

5. Conclusion 
we can say that our study corroborates that brain atrophy measurements can be incorporated into the daily basis evaluation of MS patients. Specifically T2 load and Gray Matter volume are helpful in monitoring the EDSS progression. On the other hand, we also add evidence to the importance of the cognitive impairment and volumetric changes occurring in MS, as well as the differences between the different clinical forms of the disease (greater cognitive impairment in progressive MS). Finally some results, in particular the lack of association between volumetry data and cognitive dysfunction, show the importance of continuing the research of the neurodegenerative processes of MS. 

Ethical Considerations
Compliance with ethical guidelines
All ethical principles are considered in this article. The participants were informed of the purpose of the research and its implementation stages. They were also assured about the confidentiality of their information and were free to leave the study whenever they wished, and if desired, the research results would be available to them. A written consent has been obtained from the subjects. principles of the Helsinki Convention was also observed.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.


Authors' contributions
Conceptualización, Methodology, Formal Analysis, Data Curation, Writing Original, Draft Preparation: Luis Ignacio Casanova Peño; Conceptualización, Methodology, Formal Analysis, Data Curation, Writing Original, Draft Preparation, Supervision, Project Administration, Funding Acquisition: Carlos López De Silanes De Miguel; Conceptualización, Methodology, Formal Analysis, Data Curation, Writing Original, Draft Preparation: Laura de Torres; Writing-review & editing, visualization: Miriam Eimil Ortiz, María José Gil Moreno, Beatriz Oyanguren Rodeño, Rodrigo Terrero Carpio, Blanca Patricia Díaz Montoya, Julia Sabín Muñoz, Julia Sabín Muñoz, Miguel Ángel Saiz Sepúlveda and Marta González Salaices; Software, Resources, Writing-review & editing: Esther De Antonio Sanz; Resources, writing-review & editing: Sara Abellán Ayuso.

Conflict of interest
The authors declared no conflict of interest.

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