WHITHER POST-EXERTIONAL
FATIGUE? A Comment on
The Empirical Definition and The Georgia Prevalence Study
by Cort Johnson
(06/18/07)
The
Empirical Definition has many positive aspects; better characterization of CFS
patients, a way to track treatment efficacy and perhaps identify symptom based
subsets and it does appear to identify a very ill population. But does it single
out the peculiar condition called CFS. Some aspects of it suggest to me that it
does not.
Some researchers have proposed that
post-exertional fatigue is a hallmark symptom in CFS. The Canadian Consensus and
1990 Australian definition require post-exertional fatigue to be present for a
CFS diagnosis. The Fukuda definition does not; although it is one of eight major
symptoms it is not required for a CFS diagnosis. The empirical definition
appears to dilute the importance of this symptom further. Some evidence produced
by CDC studies and others, however, suggests it is a central component of CFS.
A CDC study examining the symptoms in a
wide variety of fatigued groups (prolonged fatigue, chronic fatigue, CFS-like,
CFS) found that as the levels of fatigue increased the percentage of people
reporting ‘unusual fatigue after exercise’ did as well (Nisenbaum 2006).
That only 1.6% of people with no fatigue reported this symptom indicated it is
rarely found in healthy people. (Problems with sleep, muscle and joint pain on
the other hand were fairly common (10-20% of healthy people)). About 14% of
people with prolonged fatigue and 33% with chronic fatigue reported unusual
fatigue after exercise but from there the percentages jumped up markedly; 77 and
74% of CFS-like and CFS patients reported this symptom. This suggests there is a
big difference between chronic fatigue patients (fatigued but don’t meet 1994
criteria for CFS) on the one hand and CFS-like (met the criteria but didn’t
undergo the clinical evaluation) and CFS patients (meet the criteria, visited
the clinic) with regard to this symptom.
Similarly CDC
studies exploring the question of subsets in CFS (Conna et. al. 2006, Aslakson
et. al. 2006) found that post-exertional fatigue – was the first and third most
important differentiating variable in the PCA and Latent Class Analyses. Its
discriminatory prowess was highlighted by the fact that it and concentration
difficulties were the only variables not found at all in the Well Group. The
very high levels of post exertional fatigue (78-91%) in the three classes
dominated by CFS patients and the low to moderate levels of it (33-41%) in the
classes dominated by idiopathic fatigue patients again indicated that this
symptom plays a special role in CFS. CFS is often described as being an amalgam
of very common symptoms but these studies indicate that post-exertional fatigue
is only rarely found even a subset of the population one might expect it to; the
BMI matched overweight, obese and even morbidly obese healthy controls in this
study who presumably don’t exercise much.
Since
the ‘chronic fatigue’ group in the Nisenbaum was the largest fatigued group
studied in the Nisenbaum study (PF=575, CF=1085, CFS-like=263, CFS=43) this
group will surely account for most of the increase in the prevalence rates under
the empirical definition. This indicates that most CFS patients under the
empirical definition will not be characterized by ‘unusual fatigue after
exercise’. This is not in some ways surprising; Dr. White and Jason have
pointed out patients can meet the new criteria for CFS simply by reporting they
have low activity levels.
A Personal Response:
For the first ten years after I got CFS I, who was formerly an
avid exerciser, didn’t try to do anything more than walk. My symptoms at that
point, while very disturbing, were nevertheless mostly not that unusual
overall; I was very tired, I couldn’t concentrate well, my muscles hurt, I had
constant sore throats, I felt out of it, I wasn’t strong. Basically I felt like
I was shadow of my former self but I was able to get around, I was able to go to
school. It probably could have been argued that I had some strange mental
condition. Given the lack of information on CFS around that time – mid-1980’s,
in the back of my mind I wondered if something like that had indeed occurred.
About 10 years into the disease I did
something very unusual - I began an exercise program and have tried to do so
several times since then. Each time my response was to it has been bizarre. The
symptom exacerbation has been immense, not just at the beginning of the exercise
program but throughout. Over time I was able to increase my strength and
duration. In fact I usually felt good while I was exercising – but the aftermath
was always devastating. Starting anywhere from ½ hour to several hours later I
could feel that peculiar package of symptoms set in; the stiff, painful muscles,
the heart yammering, the uncoordination, the need to lie down, the difficulty
thinking or talking, the feelings of irritation. These symptoms would typically
peak a day or so later and then slowly subside. It is an utterly strange
response to exercise and it is the hallmark symptom of my CFS – it’s what
convinced me that there was a physiological basis to my problems.
The idea that this vital part of CFS is
being subsumed under this new definition suggests that while researchers may
uncover important aspects of unwellness by studying this population they may
very well have a very difficult time understanding the condition known as CFS.
________________________
Aslakson, E.,
Wollmer-Connar, U. and P. White. 2006. The validity of heterogeneity in chronic
unexplained fatigue. Pharmacogenomics 7, 365-373
Conna, U., Aslakson, E. and P. White.
2006. An empirical delineation of the heterogeneity of chronic unexplained
fatigue in women. Pharmacogenomics 7, 355-364.
Jason, Leonard. 2007. Problems with the
new CDC CFS Prevalence Estimates. IACFS Website.
Reeves WC, Jones JF, Maloney E, Heim C, Hoaglin DC, Boneva
RS, Morrissey M, Devlin R,
Prevalence of chronic fatigue syndrome in
metropolitan, urban, and rural Georgia.
Popul Health Metr. 2007 Jun
8;5(1):5
Reeves WC, Wagner D, Nisenbaum R, Jones JF, Gurbaxani B,
Solomon L, Papanicolaou DA, Unger ER, Vernon SD, Heim C,
Chronic fatigue syndrome--a
clinically empirical approach to its definition and study.
BMC Med. 2005
White, P. 2007. How common is chronic
fatigue syndrome; how long is a piece of string? Population Health Metrics 5:6
doi:10.1186/1478-7954-5-6