Investigate the repercussion of processing speed of information (PSI) deficit on functional impulsivity in Multiple Sclerosis (MS).

Behavioural aspects are rarely explored in MS. Dickman scale FIDI allows distinguishing functional impulsivity (FI) which is the ability to react fast and properly when it is necessary, from dysfunctional impulsivity (DI) which is the tendency to miss forethought before acting. This study aimed to explore whether MS patients significantly lack of FI or show too high DI, and the factors that may induce abnormal impulsivity.

Patients with Clinically Isolated Syndrome (CIS, n=26), Relapsing-Remitting MS (RRMS, n=33), Secondary Progressive MS (SPMS, n=25) and Primary Progressive MS (PPMS, n=25) were prospectively recruited in our university MS clinic, and filled the FIDI Dickman scale to measure FI and DI, the Fast Beck Depression Inventory for depression, and the EMIF scale for physical, cognitive and social fatigues. The Computerised Speed Cognitive Test (CSCT) was performed to measure PSI.

The whole cohort did not show pathological lack of FI nor high DI on a mean z-score (mean FI: -0.2, SD: 1.1; mean DI: 0.1, SD: 0.9). Nevertheless, 25 patients out of 109 showed a pathological lack of FI. RR patients showed significantly less FI (mean FI: -0.7, SD: 1.2) compared to the three other groups (F=8.9, p=0.004). Multiple linear regression analyses taking into account EDSS score, disease duration, depression, fatigue scores, and PSI, showed significant impacts only of cognitive fatigue (beta=-.42)  and CSCT (beta=.31) on FI (F(7;99)=9.93, p<0.000001).

MS patients, especially RRMS, tend to show a pathological lack of FI. Progressive forms of MS might lack of insight on this self-administered questionnaire. Slowing of PSI and a high cognitive fatigue tend to induce a lack of functional impulsivity in MS. PSI impacting FI highlights a link between cognition and behaviour in MS.