To examine the relationship between the cognitive subscale of the modified fatigue impact scale (MFIS-CS) and objective measures of cognition in patients with multiple sclerosis (MS).

MFIS is a validated instrument for assessment of severity of fatigue in MS; it is composed of 21 questions which span physical, cognitive and psychosocial domains. However, it remains to be determined if impairment in MFIS-CS actually correlates with objective impairments in cognition.

Fifty-four participants (20M/34F) were recruited as part of an intervention for cognitive impairment in MS. Mean age of the subjects was 43.64 years, (SD=9.77), mean education was 15.21 years (SD=2.19), and a mean EDSS step score was 3.78 (SD=1.99). Participants underwent testing with the Symbol Digit Modalities Test (SDMT), California Verbal Learning Test II (CVLT-II), and Beck Depression Inventory (BDI). Correlation with MFIS-CS was analyzed using the Pearson Correlation Coefficient in SPSS.  

Pearson correlation analyses revealed no significant relationship between MFIS-CS and SDMT (r(52) = .02, p= .88) or CVLT-II learning (trials 1-5) (r(52) = .02, p = .87). However, a significant correlation was observed between MFIS-CS and BDI-II scores (r(52) = .44, p < .001). 

These results indicate a discordance between reported cognitive fatigue and objective measures of cognitive performance in MS patients. Moreover, the correlation of the MFIS-CS with depressive symptoms is consistent with previous reports that depression may be underlying perceptions of cognitive impairment in MS patients. These findings underscore the relevance of interpreting both subjective and objective reports of patients with MS as well as their emotional status in relation to problems with fatigue.