A study of cognitive fatigue in Multiple Sclerosis with novel clinical and electrophysiological parameters utilizing the event related potential P300.

Background: Although cognitive fatigue plays a significant part in Multiple Sclerosis (MS) related impairment, knowledge regarding it is largely lacking. Until now, not many tools are available to a clinician to detect cognitive fatigue. The subjective tools of fatigue have never been reliable.tabl OBJECTIVES: To assess the prevalence and clinical/ demographic profile of cognitive fatigue in MS using novel clinical and electrophysiological measures and to find their accuracy. We also aimed to test the three leading hypotheses - the temporal fatigue, cognitive load and cognitive domain hypotheses of cognitive fatigue in MS.

Methods: 50 consecutive MS patients attending the Neurology OPD in Madras Medical College, Chennai from May 2015 to February 2016 satisfying the 2010 revised McDonald criteria for MS with an equal number of matched controls were recruited. Modified versions (a shorter version, and longer and more demanding versions) of the Stroop test, symbol digit modalities test, and serial addition tests were used in addition to modified tests of P300 latency and amplitude each specifically tailored to reveal cognitive fatigue.

Results: Out of the seven measures of cognitive fatigue used, 46% (n=23) of MS patients had impairment in two or more of the scores compared to that of 8% (n=4) in the healthy control group. The Expanded disability status scale (EDSS) scores were significantly higher for MS patients with cognitive fatigue compared to those without. All the clinical and electrophysiological measures used in this study had a relatively high sensitivity and specificity. In addition, all the clinical measures correlated with the electrophysiological measures of cognitive fatigue in this study. Our data also supported all three hypotheses implying that cognitive fatigue in MS may be a multifaceted entity.

Conclusion: Cognitive fatigue is widely prevalent in MS and can be detected with specific tools. The tools developed and described in this study may be used as an effective means of detecting cognitive fatigue in MS patients and thus allowing patients to realise their limitations. Institution of appropriate remedial measures like advising such patients to break up a more cognitively demanding task into smaller subtasks may help to improve their quality of life.