Distinguishing between Fatigue and Fatigability in Multiple Sclerosis.

Area of Science:

• Neuroscience
• Clinical Psychology

Background:

• Fatigue is a prevalent and debilitating symptom in multiple sclerosis (MS).
• Fatigue encompasses tiredness, low energy, motivation, and concentration difficulties.
• It can be assessed as a current state or a trait related to work capacity.

Purpose of the Study:

• To differentiate between the state level of fatigue and the trait level of fatigability in individuals with MS.
• To explore the neural underpinnings and measurement of fatigue and fatigability.
• To highlight the importance of distinguishing these concepts for effective MS symptom management.

Main Methods:

• Distinguishing between state fatigue (instantaneous perception) and trait fatigability (work capacity).
• Measuring perceived fatigability via questionnaires on past task performance.
• Measuring objective fatigability by assessing outcome changes during tasks.

Main Results:

• State fatigue reflects current homeostatic regulation, while fatigability relates to work capacity.
• Perceived and objective fatigability are distinct constructs.
• Elevated trait fatigue in MS is linked to interoceptive network deficits (insula, dorsal anterior cingulate cortex) and increased functional connectivity during demanding tasks.

Conclusions:

• The distinction between fatigue (state) and fatigability (trait) is crucial for understanding MS symptom burden.
• Interoceptive network function is implicated in trait fatigue in MS.
• Reward and pain pathways can modulate both state and trait fatigue levels in individuals.