368 Chronic Fatigue Syndrome
symptoms (those in the last category were younger and had a
shorter duration of the illness).
Disagreement continues about which symptoms should be
included in the CFS case de“nition. For example, Komarof f
and associates (1996) compared patients meeting the major
criteria of the original U.S. CFS case de“nition (Holmes et al.,
1988) with healthy controls and groups with multiple sclero-
sis and depression. They concluded that eliminating muscle
weakness, arthralgias, and sleep disturbance, and adding
anorexia and nausea would strengthen the case de“nition.
Jason, Torres-Harding, Carrico, et al. (2002) compared indi-
viduals with CFS, melancholic depression, and controls, and
in contrast to the Komaroff study, muscle weakness and
arthralgias were reported in over half of participants with CFS
and uniquely differentiated this group from controls. Jason,
Torres-Harding, Carrico, et al. (2002) also found that anorexia
and nausea occurred with relatively low frequency, and nei-
ther uniquely differentiated those with CFS from controls.
Others have provided experimental evidence for the
importance of the CFS criteria (Hartz, Kuhn, Levine, &
London, 1998). These authors (1998) examined persons
with CFS and compared them to those with other fatigue-
related conditions and those with no symptoms of fatigue.
They concluded that persons with fatigue could be classi“ed
by the degree to which they matched the case de“nition of
CFS (Fukuda et al., 1994). They also suggested including cri-
teria such as frequent fever and chills, muscle weakness, and
sensitivity to alcohol. Jason, Torres-Harding, Carrico, et al.
(2002) found that muscle weakness and sensitivity to alcohol
uniquely differentiated the CFS group from controls. They
also found a symptom currently not part of the Fukuda
criteria„shortness of breath. It did dif ferentiate the groups
and might play a role in neurally mediated hypotension,
which has been connected to CFS (Poole, Herrell, Ashton,
Goldberg, & Buchwald, 2000).
A study by Jason, Taylor, Kennedy, Jordan, Huang, et al.
(2001) evaluated dimensions of chronic fatigue in a strati“ed
random community-based sample of households within
ethnically diverse neighborhoods. Factor analysis of items
contained in a CFS Screening Questionnaire provided support
for the existence of four distinct components of chronic fa-
tigue. These were lack of energy (fatigue intensity), physical
exertion (fatigue exacerbated by physical exertion), cognitive
problems (dif“culties with short-term memory, concentration,
and information processing), and fatigue and rest (rest or sleep
is not restorative). Results of these analyses were of theoreti-
cal importance because two of the primary dimensions of fa-
tigue that emerged within the CFS-like group, postexertional
fatigue and cognitive problems, corresponded closely with
major de“nitional criteria for CFS (Dowsett, Goudsmit, Mac-
intyre, & Shepherd, 1994; Lloyd, Hickie, Boughton, Spencer,
& Wake“eld, 1990). Postexertional fatigue is part of the major
criteria for Myalgic Encephalomyelitis (ME; the British term
for CFS) in Great Britain (Dowsett et al., 1994), and cognitive
problems are part of the major criteria for the Australian de“-
nition of CFS (Lloyd et al., 1990). Postexertional fatigue and
cognitive problems appear to represent primary dimensions
of CFS.
A cluster analysis of the data just mentioned was per-
formed to de“ne a typology of chronic fatigue symptomatol-
ogy (Jason & Taylor, in press). With respect to CFS, “ndings
suggest that a majority of individuals with moderate to severe
symptoms can be accurately classi“ed into two impor-
tant subgroups: one distinguished by severe postexertional
fatigue and fatigue that is alleviated by rest; and one distin-
guished by severe overall symptomatology, severe postex-
ertional fatigue, and fatigue that is not alleviated by rest. One
key characteristic distinguishing the two clusters that con-
tained almost all participants with CFS from the cluster
containing only one CFS participant was markedly high
severity of postexertional fatigue. This symptom has been
designated as a major criteria for the London de“nition of
Myalgic Encephalomyelitis (Dowsett et al., 1994), but as
one of the minor criteria for the U.S. de“nition of CFS
(Fukuda et al., 1994).
Results from this investigation highlight the relative im-
portance of this symptom as a diagnostic marker for CFS and
point to the potential utility in designating postexertional
fatigue as a major criteria for CFS in future attempts to
de“ne this syndrome. A second key characteristic, fatigue in
relation to rest, distinguished individuals in two clusters that
contained individuals with CFS, but those in one cluster dif-
fered most signi“cantly from those in the second cluster with
respect to whether their fatigue was alleviated by rest. One of
the major criteria for the current U.S. de“nition of CFS
(Fukuda et al., 1994) is that fatigue is not substantially allevi-
ated by rest. Findings from this investigation suggest that this
criteria may be more accurately designated as one of the
minor criteria for CFS so that it does not arti“cially exclude
those with CFS who may experience some symptom relief
with rest. A third result deserving attention involves the “nd-
ing for more severe cognitive problems in the clusters with
patients with CFS versus the cluster with only one patient
with CFS. This “nding highlights the importance of cognitive
problems to the experience of CFS and supports the designa-
tion of cognitive problems as a major criteria for CFS in the
London (Dowsett et al., 1994) and Australian (Lloyd et al.,
1990) criteria.