Analysing the relationship between polysomnographic measures of sleep with measures of physical and cognitive fatigue in people with multiple sclerosis.

OBJECTIVES: We aimed to determine whether there was a relationship between objective measures of sleep measured by polysomnography and measures of physical and cognitive fatigue in patients with Multiple Sclerosis (MS).

METHODS: People with MS of age 18-50 years of any subtype attending the OPD satisfying the revised 2010 McDonald criteria were recruited. Modified Fatigue Impact Scale (MFIS) and the Fatigue Severity Scale (FSS) were used to assess physical fatigue. Cognitive fatigue was measured with modified versions of the Stroop test, modified Symbol Digit Modalities Test, Serial Addition Test, and with latency and amplitude of the P300 evoked potential. Percentage of N1, N2, N3 and REM sleep stages, Sleep onset latency, Sleep efficiency, Wake after sleep onset, Respiratory event index, Periodic limb movement index were the measures recorded with polysomnography.

RESULTS: Among 113 patients, 43 (38.05%) complained of disturbed sleep and 88 (77.88%) complained of increased fatigability and tiredness. Mean MFIS score of the sample was 42.34 ± 9.09. Mean FSS score was 19.12 ± 9.42. Polysomnographic measures of sleep showed a significant correlation with objective measures of cognitive fatigue and did not show any significant correlation with measures of physical fatigue.

CONCLUSIONS: Sleep impairment is a very common problem in people with MS justifying routine polysomnographic evaluation. We have found evidence that though sleep impairment is not related to physical fatigue, it is strongly related to cognitive fatigue.