Operationalising cognitive fatigability in multiple sclerosis: A Gordian knot that can be cut?

Abstract

Background: Researchers have attempted to operationalise objective measures of cognitive fatigability in MS to overcome the perceived subjectivity of patient reported outcomes of fatigue (PROs). Measures of cognitive fatigability examine decrements in performance during sustained neurocognitive tasks.Objective: This editorial briefly summarises available evidence for measures of cognitive fatigability in MS and considers their overall utility.Results: Findings Studies suggest there may be a construct that is distinct from self-reported fatigue, reflecting a new potential intervention target. However, assessments vary and findings across and within measures are inconsistent. Few measures have been guided by a coherent theory, and those identified are likely to be influenced by other confounds, such as cognitive impairment caused more directly by disease processes, depression, and assessment biases.Conclusions: Future research may benefit from (a) developing a guiding theory of cognitive fatigability, (b) examining ecological and construct validity of existing assessments, and (c) exploring whether the more promising cognitive fatigability measures are correlated with impaired functioning after accounting for possible confounds. Given the issues raised, we caution that our purposes as researchers may be better served by continuing our search for a more objective cognitive fatigability construct that runs in parallel with improving, rather than devaluing, current PROs.

Neural correlates of effort-dependent and effort-independent cognitive fatigue components in patients with multiple sclerosis

“…Both forms of fatigue can be separated into an effort-independent general subjective sensation of fatigue, and fatigability as an effort-dependent change in performance. 5 Functional imaging work on different fatigue types 6 provided at least in part conflicting results. Some found a correlation between fatigue and brain atrophy or lesion load.…”

Cognitive Fatigability Interventions in Neurological Conditions: A Systematic Review

“…Third, they suggested that research explore whether the more promising CF measures are correlated with impaired functioning after accounting for possible confounds. Fourth, they highlighted the need for outcome assessments to be able to identify clinically meaningful improvement [109]. A last point made by Harrison et al that we wish to echo here is that the quest for improving the objective measurement of CF does not imply that subjectively measured fatigue is somehow less relevant or important [109].…”

“…As previously stated, the study of fatigue in neurological conditions is fraught with varying definitions and methodology that highlight the need for a clear conceptual framework from which to guide further study. Harrison et al [109] summarized the available evidence for measures of CF in MS and made the following recommendations. First, they called for the development of a guiding theory of CF that considers differences between primary and secondary fatigue and broader psychosocial models.…”

“…Fourth, they highlighted the need for outcome assessments to be able to identify clinically meaningful improvement [109]. A last point made by Harrison et al that we wish to echo here is that the quest for improving the objective measurement of CF does not imply that subjectively measured fatigue is somehow less relevant or important [109]. Clearly, patient perceptions of their own experience should be guiding both clinicians in terms of helping them manage their symptoms, and researchers by ensuring that research questions address concerns that are relevant to the patient populations under study.…”

Cognitive fatigability is a quantifiable distinct phenomenon in multiple sclerosis

“…Further, it is still debated whether cognitive fatigability may represent an aspect of cognitive impairment rather than a distinct phenomenon. Within this framework, the lack of reliable measures and the need for an objective index of cognitive fatigability have been highlighted (Harrison, das Nair, & Moss‐Morris, ). An accurate characterization of all aspects of fatigue, indeed, may guide in the selection of specific and tailored treatments (Manjaly et al , ).…”