Just stumbled across this while searching for something else and thought cross-posting here was in order:
A suggestion to differentiate and precisely specify diverse forms of fatigue, based on detailed symptoms monitoring (*)
Fatigue often is seen as one of the most characteristic symptoms of ME/CFS. While the focus on fatigue has been criticized, to me it still seems justified to list diverse forms of fatigue and fatigability among the core symptoms of ME/CFS. Yet I think fatigue as a symptom, or complex of symptoms, should always be specified.
It seems to me that most clinicians and researchers conceive fatigue as basically being one feature, consisting of two subtypes: an adequately perceived fatigue and an inadequately perceived fatigue. (Perhaps similar to the conception of pain .)
The first subtype is acknowledged to have an underlying pathophysiology whereas the second subtype is seen as a merely distorted perception of normal bodily and cognitive functions, a perception that lets people do less than they actually could do and makes them avoid certain triggers. Often, the associated claim is that the distorted perception can be normalized again by thinking and/or behaving differently, and to achieve this cognitive therapy or graded exposure to the triggers or both is needed,
At the same time, most researchers I think admit that their ideas how the physiology of 'fatigue' in chronic illness works are still only hypotheses. Fatigue still mostly seems "medically unexplained".
Yet there were some attempts to specify and differentiate manifestations of MS related fatigue which I think could make sense, because they aren't based on premature ideas about the etiology, but on precise observations, and objective measurement derived from those observations. [1,2,4]
I'm afraid though that those attempts to differentiate also apply the underlying concept of adequate and inadequate perceptions as a means to either acknowledge or dismiss them as
medical problems. Which maybe doesn't matter so much for the specific features they study if they are seen as 'adequately perceived' fatigue -- as it more often seems to be the case with motor fatigability and cognitive fatigability in MS and other neurological illness.
However, these approaches seem to me to imply that similar symptoms in the same illness or in a comorbidity (or in another illness that is framed as 'medically unexplained' per se) are not worthy to be differentiated and assessed in a similarly elaborated manner, if they are seen only as a a distorted perception. They then are being denied the possibility of objectively measurable 'real' alterations or of any other relevant objective measures.
Moreover, even the suggestions to differentiate made e.g. by Kluger er al [3] apparently aim at establishing a comparable, unified category of 'fatigue' as a summary of all forms of fatigue and fatigability.
I think it would be extremely helpful to work on a critique on the concept(s) of fatigue in chronic illnesses, validating the idea of differentiating and speaking of fatigue only with a specifier. Also perhaps, validating the importance of both improving the quality of subjective reports and applying objective measures of specific symptoms associated with 'fatigue', no matter if it is associated with a known underlying pathophysiology or not. If some types of fatigue did occur only as a distorted perception, the mechanisms of that distortion would also neeed to be properly investigated before claims on how it could be altered are made.
In ME/CFS however, specifying diverse forms of fatigue (also in more complex symptoms like PEM which consists of diverse symptoms, including symptoms that cannot be sufficiently described even with differentiated, specified terms of fatigue) I think need to be preceded by more precise observations.[5]
Observations could include cognitive activity and physical activity patterns over a period of time (several weeks at least), accompanied by observation of movement patterns [6] (including fine motor skills) and repeated testing of diverse dimensions of cognitive performance, all compared with both healthy controls and other illness, e.g, depression.
These diverse observations and measurements I think have to be seen together to not only develop useful tools for a more robust diagnosis but also to get better clues where to look for potential pathophysiological factors.
References:
[1] Sehle, A., Vieten, M., Sailer, S. et al (2014), Objective assessment of motor fatigue in multiple sclerosis: the Fatigue index Kliniken Schmieder,
J Neurol 261: 1752.
https://doi.org/10.1007/s00415-014-7415-7,
[2] Dettmers, C. , Riegger, M. , Müller, O. and Vieten, M. (2016), Fatigability Assessment Using the Fatigue Index Kliniken Schmieder (FKS) Is Not Compromised by Depression.
Health , 8, 1485-1494. doi:
10.4236/health.2016.814147.
[3] Kluger BM, Krupp LB, Enoka RM (2013), Fatigue and fatigability in neurologic illnesses: proposal for a unified taxonomy.
Neurology. , 80 (4): 409-16,
https://n.neurology.org/content/80/4/409 ; PMC article:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3589241/
Related discussions on S4ME:
[4] Objective assessment of diverse types of MS related fatigue and fatiguability,
https://www.s4me.info/threads/objec...of-ms-related-fatigue-and-fatiguability.4241/
[5] Measuring fatigue. Discussion of alternatives to questionnaires:
https://www.s4me.info/threads/measuring-fatigue-discussion-of-alternatives-to-questionnaires.7325/
[6] suggestion on how to use accelerometers:
https://www.s4me.info/threads/measu...ernatives-to-questionnaires.7325/#post-130804
(*)
This is an amended version of a comment made in reference [4], and a later edites version of my submission to the ME/CFS PIP discussed here.:
Later edit: "[...] whereas the second subtype is seen as a mere distortion of normal bodily and cognitive functions. --> whereas the second subtype os seen as a merely distorted perception of normal bodily and cognitive functions ...[+ more edits in this and the following sentence.]
Latest edits --added content:
"I'm afraid though that those attempts to differentiate also apply the underlying concept of adequate and inadequate perceptions
as a means to either acknowledge or dismiss them as medical problems."
"
If some types of fatigue did occur only as a distorted perception, the mechanisms of that distortion would also need to be properly investigated before claims on how it could be altered are made."