14. Chronic fatigue syndrome
- 14.1 Aim
- 14.2 Research questions
- 14.3 Definitions and classification of fatigue
- 14.4 Results
- 14.5 Discussion
14.1 Aim
The aim of this analysis is to investigate whether male Australian Defence Force personnel who served in the Gulf War have a higher rate of chronic fatigue syndrome than the comparison group; and, if so, whether this is associated with exposures and experiences that occurred in the Gulf?
14.2 Research questions
1. Do Australian Gulf War veterans have significantly more chronic fatigue syndrome than the comparison group?
2. Is chronic fatigue syndrome in Gulf War veterans associated with exposure to chemical or environmental agents, infectious agents or the use of prophylactic medications or immunisations?
3. Does the immunological profile of Gulf War veterans with chronic fatigue syndrome differ from that of comparison group subjects with chronic fatigue syndrome?
14.3 Definitions and classification of fatigue
The methodological approach to the assessment of chronic fatigue in this study was based on the criteria for the epidemiological investigation of chronic fatigue syndrome as recommended by Fukuda et al.[305] The assessment of fatigue and chronic fatigue outcomes in this study was based on:
- a HSA doctor’s standardised interview of the participant to establish a history of fatigue and chronic fatigue and to assess the severity of the fatigue and the presence of associated symptoms.
- a medical evaluation of the history, physical examination, psychological assessment and laboratory investigations on all cases of chronic fatigue to determine whether there was a medical or psychological condition that may explain the chronic fatigue, with the doctor undertaking this evaluation blinded to the Gulf War status of the subjects,
- other exposure and health outcomes data for the purposes of subgrouping cases of chronic fatigue syndrome.
14.3.1 Definitions of fatigue and chronic fatigue syndrome
For the purpose of this study, the following definitions, based on those developed by Fukuda et al,[305] were used to define various states of fatigue and chronic fatigue syndrome. By definition, all subjects who met the following criteria would have experienced extreme tiredness or fatigue at some time in the past 12 months.
Fatigue
Participants were defined as having fatigue if, in the past 12 months, the participant had experienced extreme tiredness or fatigue following his normal activities.
Prolonged fatigue
Participants were defined as having prolonged fatigue if, in the past 12 months, the participant had felt extremely tired or fatigued following his normal activities every day, or almost every day, for one month or longer.
Chronic fatigue
Participants were defined as having chronic fatigue if the participant had had a period(s) of extreme tiredness or fatigue that had been persistent, relapsing or recurring for a total duration of at least 6 months or more since it first began.
Medically explained chronic fatigue and medically unexplained chronic fatigue
Participants were defined as having:
- medically explained chronic fatigue if the participant had chronic fatigue that could be explained by a medical or psychological condition according to the medical evaluation.
- medically unexplained chronic fatigue if the participant had chronic fatigue that had not been explained by a medical or psychological condition according to the medical evaluation.
Chronic fatigue syndrome
Participants were defined as having chronic fatigue syndrome if the participant had medically unexplained chronic fatigue that was of new or definite onset (had not been lifelong), and
- the participant met the criteria for the severity of fatigue, that is the feeling of extreme tiredness or fatigue was not substantially alleviated by rest (they had some recovery, no recovery or their fatigue was worse following rest, sleep or relaxation), and resulted in substantial reduction in previous levels of occupational, educational, social or personal activities (they were able to do <75% of their normal activities during these periods of extreme tiredness or fatigue), and
- the participant had experienced at least four or more of the following
symptoms, which had not predated the fatigue, and each of which had
been present for at least a total of 6 months, and the four or more
symptoms had been present concurrently for at least 6 consecutive months:
- Self-reported impairment in short-term memory or concentration
- Sore throat
- Tender cervical or axillary lymph nodes
- Muscle pain
- Multi-joint pain without joint swelling or redness
- Headaches of a new type, pattern or severity
- Unrefreshing sleep
- Post-exertional malaise lasting more than 24 hours.
Idiopathic chronic fatigue
Participants were defined as having idiopathic chronic fatigue if the participant had medically unexplained chronic fatigue that did not meet the severity or symptom criteria for chronic fatigue syndrome.
The steps in the process of defining cases of chronic fatigue syndrome in this study, based on the Fukuda et al criteria,[305] are summarised in Figure 14.1. These steps in the process were undertaken without knowing the Gulf War status, which was revealed at the end of the process.
back to topFigure 14.1 Process for defining cases of chronic fatigue syndrome
View figure 14.1 (42 kb)
14.4 Results
14.4.1 Fatigue and chronic fatigue syndrome
One female study participant was identified as having chronic fatigue and this is reported in chapter 15. The following results refer to males only.
Table 14.1 shows that Gulf War veterans reported all fatigue-related health outcomes more commonly than the comparison group. Gulf War veterans reported more extreme tiredness or fatigue at any time in the last 12 months, more prolonged fatigue, and were identified as having more chronic fatigue, than the comparison group. The proportion of subjects reporting an increasing duration of fatigue decreased steadily in both groups. The risk of Gulf War veterans having chronic fatigue, which was not considered to be explained by a medical or psychological condition, was more than twice that of the comparison group. The risk of Gulf War veterans having chronic fatigue syndrome according to the study criteria was five times that of the comparison group. The odds ratios increased with increasing refinement and clinical evaluation of the nature of the fatigue. The numbers of cases of chronic fatigue syndrome were small, especially in the comparison group, and need to be interpreted with caution.
| GWV N=1382* | Comp grp N=1377* | Crude OR | Adj OR† | 95% CI | P value | |||
|---|---|---|---|---|---|---|---|---|
| n | % | n | % | |||||
| Fatigue in the last 12 months |
262
|
19.0
|
159
|
11.5
|
1.8
|
1.7
|
1.4-2.2
|
<0.001
|
| Prolonged fatigue (>= 1 month) |
132
|
9.6
|
74
|
5.4
|
1.9
|
1.8
|
1.3-2.5
|
<0.001
|
| Chronic fatigue (>= 6 months) |
109
|
7.9
|
58
|
4.2
|
2.0
|
1.9
|
1.4-2.7
|
<0.001
|
| Unexplained chronic fatigue* |
92
|
6.7
|
40
|
2.9
|
2.4
|
2.3
|
1.6-3.5
|
<0.001
|
| Idiopathic chronic fatigue |
77
|
5.6
|
37
|
2.7
|
2.1
|
2.1
|
1.4-3.2
|
<0.001
|
| Chronic fatigue syndrome |
11
|
0.8
|
2
|
0.1
|
5.5
|
5.0‡
|
1.1-47.4
|
0.036
|
* There were minor variations in the ‘n’ for
each fatigue-related outcome because small numbers of missing variables
meant that the outcome could not be computed (4 Gulf War and 1 comparison
group subject had missing values or ‘don’t know’ information
for one or more of the severity or symptom criteria for assessing chronic
fatigue syndrome) or data for computation of adjusted odds ratios were
not available on up to 30 participants.
† Odds ratios were adjusted for age (<20, 20-<25, 25-<35,
>=35 years), service type, rank, education, marital status, smoking
(current, former, ever) and alcohol (AUDIT score >8)
‡ Odds ratio obtained by exact logistic regression adjusting for
age (<25, >=25 years), service type and rank
One hundred and sixty-seven male subjects (109 Gulf War veterans and 58 comparison group subjects) were identified as having chronic fatigue (Table 14.1). A medical or psychological condition that could have explained the chronic fatigue, after a blinded medical review, was identified in 35 subjects (17 Gulf War and 18 comparison group subjects), and these are summarised in Table 14.2.
There were a wide variety of medical or psychological conditions that were assessed as explaining the chronic fatigue. The number of subjects with each condition was small.
back to top|
Medical or psychological conditions
|
n |
|---|---|
|
Alcohol or other substance abuse
|
|
| Alcohol abuse* | 4 |
|
Active medical conditions†
|
|
| Cancer | 5 |
| Neurological conditions | 2 |
| Gastrointestinal conditions | 1 |
| Endocrine condition | 1 |
| Respiratory condition, including uncontrolled asthma (>=30 attacks in the last 12 months) |
3 |
|
Psychological conditions (with no active medical
condition)
|
|
| Bipolar I disorder, Manic | 7 |
|
Sleep apnoea or narcolepsy
|
|
| Self-reported sleep apnoea or narcolepsy‡ | 8 |
|
Others
|
|
| Physical labour/exertion or lifestyle changes | 4 |
* Alcohol abuse had been diagnosed by the CIDI and had
had an onset within 2 years before the onset of the chronic fatigue and
at any time afterward
† Of those with an active medical condition assessed as explaining
the fatigue, one subject also had sleep apnoea, and two other subjects
also had Bipolar I disorder, Manic.
‡ Self-reported narcolepsy or sleep apnoea was considered as a possible
explanation for the chronic fatigue if it was rated as a possible or probable
diagnosis by a HSA doctor and been assessed as having the potential to
explain the chronic fatigue from a chronological perspective
Of the eleven Gulf War veterans assessed as having chronic fatigue syndrome, ten were Navy and one was Army. Of the two comparison group participants assessed as having chronic fatigue syndrome, one was from the Navy and one was from the Army.
14.4.1.1 Fitness test results
The fitness test was used as an objective measure of fitness and fatigability. The results for the two study groups overall are presented in the General Health chapter. Of the 11 Gulf War veterans with chronic fatigue syndrome, seven were assessed by a HSA doctor as fit to perform the fitness test, and all completed the 3-minute test. Fatigue was given as a reason for not performing the fitness test in one Gulf War veteran, and for the others the reasons related to medical or musculoskeletal problems. Three of these Gulf War veterans had mean recovery heart rates in the ‘low’ fitness category and four had mean recovery heart rates in the ‘medium’ fitness category. One of the two comparison group subjects with chronic fatigue syndrome was assessed as fit to perform the fitness test, and a musculoskeletal problem was given by the other as a reason for not performing the test. The comparison group subject who did perform the test had a mean recovery heart rate in the ‘medium’ fitness category. These numbers are small and should be interpreted with caution.
14.4.2 Immunological profile of cases of chronic fatigue syndrome
The immunological profile of Gulf War veteran and comparison group cases of chronic fatigue syndrome was compared using lymphocyte subsets. Table 14.3 shows the mean and standard deviations of lymphocyte subset expressed as absolute cell counts and as a percentage of the total lymphocyte count (lymphocyte %). The mean cell counts of white blood cell, lymphocytes and lymphocyte subsets were similar for Gulf War veterans and the comparison group, and were within the reference intervals for both study groups, except for CD16+/CD56+CD3- which was very slightly below the reference interval in both study groups. When expressed as a percentage of total lymphocytes, all mean lymphocyte percentages were similar in Gulf War veterans and the comparison group. The mean lymphocyte percentages were all also within their reference intervals, except for CD19, a B cell marker, which was slightly elevated in both study groups.
back to top| Gulf War veterans (N=11) | Comp grp (N=2) | |||
|---|---|---|---|---|
|
Parameter
|
mean | (SD) | mean | (SD) |
| Cell counts | ||||
| White cell count (4.0-11.0 x 109/L) |
7.2
|
(1.8)
|
6.7
|
(0.7)
|
| Lymphocyte count (1.0-4.0 x 109/L) |
2.2
|
(0.6)
|
2.1
|
(0.2)
|
|
T cell markers
|
||||
| CD3 (0.66-3.22 x 109/L) |
1.7
|
(0.4)
|
1.6
|
(0.2)
|
| CD4+CD3+ (0.41-2.21 x 109/L) |
1.1
|
(0.3)
|
1.0
|
(0.01)
|
| CD8+CD3+ (0.17-1.33 x 109/L) |
0.5
|
(0.2)
|
0.5
|
(0.2)
|
|
B cell markers
|
||||
| CD19 (0.30-0.53 x 109/L) |
0.4
|
(0.2)
|
0.4
|
(0.1)
|
|
Natural Killer Cell markers
|
||||
| CD16+CD3-, x 109/L* |
6.1
|
(3.0)
|
4.0
|
(0.0)
|
| CD56+CD3-, x 109/L* |
5.0
|
(2.9)
|
4.0
|
(1.4)
|
| CD16+/CD56+CD3- (0.15-0.46 x 109/L) |
0.1
|
(0.08)
|
0.1
|
(0.02)
|
| % lymphocytes | ||||
|
T cell markers
|
||||
| CD3 (44-90%) |
74.6
|
(7.5)
|
77.0
|
(1.4)
|
| CD4+CD3+ (27-63%) |
48.1
|
(8.5)
|
50.5
|
(5.0)
|
| CD8+CD3+ (11-38%) |
23.8
|
(5.6)
|
24.0
|
(8.5)
|
|
B cell markers
|
||||
| CD19 (2-15%) |
16.0
|
(6.6)
|
17.5
|
(0.7)
|
|
Natural Killer Cell markers
|
||||
| CD16+CD3-, x 109/L* |
6.1
|
(3.0)
|
4.0
|
(0.0)
|
| CD56+CD3-, x 109/L* |
5.0
|
(2.9)
|
4.0
|
(1.4)
|
| CD16+/CD56+CD3- (1-13%) |
6.5
|
(2.8)
|
4.0
|
(1.4)
|
*IMVS does not report a reference interval for these lymphocyte subsets
Table 14.4 shows the prevalences of lymphocyte subset cell counts in relation to the laboratory reference intervals. Almost half of the Gulf War veteran group cases of chronic fatigue syndrome had CD19 (B cell marker) and CD16+/CD56+CD3- (Natural Killer Cell marker) cell counts lower than the reference intervals, whilst 2 cases had a CD19 count higher than the reference interval. Both comparison group cases of chronic fatigue syndrome had CD16+/CD56+CD3- marker cell counts lower than the reference interval. The white cell counts, lymphocyte counts and T cell marker counts of both study group cases of Gulf War veterans and comparison group cases of chronic fatigue syndrome were within the reference intervals.
| Gulf War veterans (N=11) | Comparison group (N=2) | |||
|---|---|---|---|---|
|
Parameter (cell counts)
|
n | (%) | n | (%) |
| White cell count within ref interval (4.0-11.0 x 109/L) |
11
|
(100.0)
|
2
|
(100.0)
|
| Lymphocyte count within ref interval (1.0-4.0 x 109/L) |
11
|
(100.0)
|
2
|
(100.0)
|
|
T cell markers
|
||||
| CD3 within ref interval (0.66-3.22 x 109/L) |
11
|
(100.0)
|
2
|
(100.0)
|
| CD4+CD3+ within ref interval (0.41-2.21 x 109/L) |
11
|
(100.0)
|
2
|
(100.0)
|
| CD8+CD3+ within ref interval (0.17-1.33 x 109/L) |
11
|
(100.0)
|
2
|
(100.0)
|
|
B cell marker
|
||||
| CD19 within ref interval (0.30-0.53 x 109/L) |
4
|
(36.4)
|
2
|
(100.0)
|
| <0.30-0.53 x 109/L |
5
|
(45.5)
|
0
|
(0.0)
|
| >0.30-0.53 x 109/L |
2
|
(18.2)
|
0
|
(0.0)
|
|
Natural Killer Cell marker
|
||||
| CD16+/CD56+CD3- within ref interval (0.15-0.46 x 109/L) |
6
|
(54.5)
|
0
|
(0.0)
|
| < 0.15-0.46 x 109/L |
5
|
(45.5)
|
2
|
(100.0)
|
14.4.3 Gulf War veteran group subanalysis
The small number of cases of chronic fatigue syndrome in Gulf War veterans was considered too small to undertake further subanalysis in relation to exposures and experiences that occurred in the Gulf War.
14.5 Discussion
This analysis has compared fatigue-related health outcomes between the Gulf War veterans and the comparison group. The main finding is that Gulf War veterans report more fatigue at all duration and levels of fatigue considered in this study. Gulf War veterans have been assessed as having more extreme tiredness or fatigue following normal activities in the past 12 months, more prolonged fatigue, more chronic fatigue, more chronic fatigue which had not been explained by a medical or psychological condition according to the medical evaluation, and more chronic fatigue syndrome than the comparison group. The number of subjects assessed as having chronic fatigue syndrome is small, and needs to be interpreted with caution. There are some differences between Gulf War veterans and the comparison group, and for both study groups, in relation to laboratory reference intervals for two of the lymphocyte subsets that were used to assess immunological function in this study; but the clinical significance of these is uncertain and further interpretation is limited because of the small numbers involved.
Fatigue in the past month was one of the most common symptoms that was self-reported by both Gulf War veteran (66%) and comparison group (56%) subjects in the postal questionnaire in our study. These proportions are considerably higher than those who reported that they had experienced extreme tiredness or fatigue following their normal activities in the past 12 months when interviewed by a HSA doctor (19.0% vs 11.5%). As reported in the General Health chapter, a similar proportion of Gulf War veterans and comparison group subjects self-reported that they have had chronic fatigue syndrome, that had been diagnosed in 1991 or later {13 (1%) vs 17 (1%)}; and self-reported that they have had chronic fatigue syndrome, that had been diagnosed in 1991 or later, and was assessed as a possible or probable diagnosis by a HSA doctor {10 (1%) vs 9 (1%)}. Unlike the chronic fatigue syndrome results presented in this chapter where, by definition, extreme tiredness or fatigue must have been present at some time in the last 12 months, the self-reported chronic fatigue syndrome condition may not have been current or have been experienced in the past 12 months.
The small number of subjects with chronic fatigue syndrome, according to the study definition, in both study groups limited the subgrouping of cases according to parameters such as comorbid conditions, duration of fatigue, and current level of physical functioning. We did investigate the immunological profile of Gulf War veterans and comparison group subjects using lymphocyte subsets. The mean CD19 lymphocyte subset for both study groups were slightly higher than the IMVS reference interval, and the mean CD16+/CD56+CD3- interval for both groups was very slightly lower than the IMVS reference interval. Almost half the Gulf War veteran cases of chronic fatigue syndrome had CD19, a B cell lymphocyte marker, test results that were lower than the laboratory reference interval. Almost half the Gulf War veteran cases and both the comparison group cases of chronic fatigue syndrome had CD16+/CD56+CD3-, a Natural Killer cell marker, test results that were lower than the laboratory reference interval. The white cell, total lymphocyte and T cell lymphocyte subset parameters of Gulf War veterans and comparison group were similar. Both the numbers of subjects assessed as having chronic fatigue syndrome and the number of test results outside the reference interval are small, and the significance of these findings is uncertain.
The reference intervals for lymphocyte have a number of limitations, and are being reviewed by IMVS. The reference intervals for lymphocyte subpopulations were established through testing of between 20-120 people for whom a specific test relevant to the diagnosis of arthritis had been ordered by their doctors. Lymphocyte subpopulation levels can vary on a day to day basis and diurnally. Large variations in the levels of lymphocyte parameters can be caused by external factors such as sleep, intercurrent viral illness, exercise and depression. Thus, shifts in the levels of lymphocyte subpopulations are of most use in monitoring individuals over time or if the changes are marked. The interpretation of small changes in lymphocyte levels, and interpretations against reference intervals, is considered to be more difficult.
Fatigue as a self-reported symptom and chronic fatigue or chronic fatigue syndrome as a medical condition has been reported by several of the overseas studies. The approach to defining cases of chronic fatigue syndrome and the other states of fatigue that was used in our study, was based on the Fukuda et al criteria[305] which were developed by an International Chronic Fatigue Syndrome Study Group in recognition of the need for a comprehensive and systematic approach to the definition and study of chronic fatigue syndrome. Other Gulf War health epidemiological research groups[16, 73] and recent clinical practice guidelines[391] have based their definitions of chronic fatigue syndrome on these criteria. These clinical practice guidelines have also discussed managing patients with chronic fatigue syndrome.
Previous studies have found that reports of fatigue-related symptoms are common in Gulf War veterans. Symptoms of fatigue, tiredness, lacking in energy, needing to rest more or feeling unusually sleepy/drowsy have been reported as symptoms by up to 50% of Gulf War veterans in several studies[20, 21, 160] and more frequently than by the non-Gulf comparison groups. The proportions of Gulf War veterans (66%) and comparison group (56%) subjects self-reporting fatigue as a symptom in our study is greater. Extreme fatigue every day, or almost every day, was reported by 23% of Iowa Gulf War veterans and 9% of non-Gulf veterans,[160] and these results are similar to those of our study (19.0% vs 11.5%). Fatigue lasting 24 hours was reported by 20% of US Gulf War veterans.[20] In UK Gulf War veterans, feelings of tiredness were the most troublesome symptoms, with the highest mean symptom scores, in both the Gulf War veteran and comparison groups, although as with all other symptoms the score was higher in the Gulf War veteran group.[157] Being “overly tired/lack of energy” was reported by 22.2% of a New England cohort of Gulf War veterans, but by 78.2% of a high symptom group and by 30.7% of a moderate symptom group within this cohort.[159] Thus, there is considerable variation in the proportions reporting fatigue-related symptoms in these overseas studies, but the questions used to assess these symptoms were also different.
Previous overseas studies have also found that fatigue-related medical conditions are more common in Gulf War veterans. Chronic fatigue syndrome or myalgic encephalitis was self-reported as a medical condition by 3.3% of UK Gulf War veterans.[21] Gulf War veterans were more likely than the Bosnia and Era cohort to have substantial fatigue (OR 2.2; 95% CI 1.9-2.6 and OR 3.6; 95% CI 3.2-4.2 respectively) according to their scores on the Chalder fatigue scale.[21, 230] Between 1.0-2.9% of Gulf War veterans reported symptoms consistent with chronic fatigue as a medical condition {prevalence difference all subjects 1.4 (0.9-2.0)}, and the differences between the Gulf War and comparison groups were more marked in the National Guard/Reserve than in the regular military.[16] All the criteria for chronic fatigue syndrome were met by 8 subjects in a study of 1155 Gulf War veterans and 2520 non-deployed personnel that investigated the prevalence of a chronic multisymptom illness, for which chronic fatigue was a key feature. Of these, 7 also were classified as severe cases and 1 as a mild-moderate case of this chronic multisymptom illness.[73] Whilst direct comparisons of our findings with those of previous studies are limited because of the different definitions used, chronic fatigue syndrome is self-reported less commonly by Australian than UK Gulf War veterans, but the risk of chronic or substantial fatigue is similar in Australian and overseas Gulf War veterans.
Thus, although fatigue as a symptom and as a medical condition has been reported to be more common among Gulf War veterans than non-Gulf veterans in previous studies, comprehensive and clinical evaluation of fatigue or chronic fatigue in these studies of Gulf War veterans has been limited. The risk of chronic fatigue syndrome in Gulf War veterans in our study (adjusted OR 5.0) is greater than the risk of chronic fatigue-related medical conditions that have been reported in any of these overseas studies.
The prevalence of chronic fatigue in primary care has been estimated to be 5.7%-27%.[391] The proportions of both study groups in our study reporting chronic fatigue (7.9% vs 4.2%) are at the lower end of the estimates.[391] The community prevalence of chronic fatigue syndrome in US and UK populations has been estimated to be 0.2% to 0.7%[391] and this prevalence is slightly lower than that found in our Gulf War veteran study group (0.8%) but similar to that found in our comparison group (0.1%). These study populations are, however, different to those of our study; and a strength of our study is the use of a comparison group to whom the same definitions were applied in the same manner.
Although the cause of chronic fatigue syndrome remains unexplained, an association with a variety of immunological changes have been reported.[231] It has been hypothesised that chronic fatigue symptoms reported by veterans may be due to a shift in the T cell cytokine profile from a Th1 to a Th2 response.[228] As discussed in chapter 4, one stimulus that has been proposed as a potential instigator of this shift in cytokine production is administration of Th2-inducing vaccines, particularly those with a large antigen load (eg plague, anthrax, typhoid, tetanus and cholera) and/or those which used pertussis as an adjuvant. Another potential stimulus proposed is stress, as cortisol drives a Th2 response. Exposure to carbamate or organophosphate insecticides has also been suggested as a possible trigger, as these compounds inhibit IL-2 driven events required for Th1 function.[228]
A few studies have examined this in Gulf War veterans. One of these examined the peripheral blood T-cell cytokine production and the NK cell activity of Danish Gulf War veterans and found no difference between Gulf War veterans and controls.[168] However, the investigators did not specify whether or not the veterans included in the study had somatic or psychological symptoms. Another study[169] examined T cells, B cells, NK cells and cytokines in individuals with chronic fatigue syndrome (either Gulf War or non-Gulf War veterans) and in healthy Gulf War or non-Gulf War veteran controls. The authors concluded that there was no evidence of immune dysfunction in sporadic chronic fatigue syndrome, but that Gulf War veterans with severe fatiguing illness did have an altered immune function, although their results were still within the normal range.
Even though some of the other studies have done further tests, eg cytokine levels, the similarity of our results for CFS cases in the Gulf War veterans and the comparison group do not provide a strong rationale for further laboratory investigation of these cases at this stage.
14.5.1 Summary of findings
In summary, and in answer to the research questions, Australian Gulf War veterans have significantly more chronic fatigue syndrome than the comparison group according to the definition based on the Fakuda et al criteria used in our study, but the numbers were very small. Gulf War veterans also have significantly more prolonged fatigue, chronic fatigue, and medically unexplained chronic fatigue that did not fulfil the severity or associated symptoms criteria for chronic fatigue syndrome, ie more idiopathic chronic fatigue, than the comparison group.
The number of Gulf War veterans with chronic fatigue syndrome was too small to undertake further subanalysis in relation to exposures or experiences that occurred in the Gulf War.
The immunological profile of Gulf War veterans with chronic fatigue syndrome differed to that of comparison group subjects with chronic fatigue syndrome on one lymphocyte subset, (CD19, a B cell marker), but the clinical significance of this is uncertain.
The reasons for the increased risk of all fatigue-related conditions in Gulf War veterans are not obvious from the limited subgrouping according to lymphocyte subsets that could be done given the small numbers of cases of chronic fatigue syndrome. We would like to undertake further evaluation of cases of chronic fatigue and idiopathic fatigue, for whom there are greater numbers of subjects, to investigate the characteristics and exposures of those at increased risk.
back to top