IJE Advance Access originally published online on April 25, 2005
International Journal of Epidemiology 2005 34(4):810-819; doi:10.1093/ije/dyi084
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Article |
Neurological status of Australian veterans of the 1991 Gulf War and the effect of medical and chemical exposures
1 Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia
2 Department of Neurology, Austin Health, Heidelberg, Victoria, Australia
3 Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia
* Corresponding author. Department of Epidemiology and Preventive Medicine, Monash University—Central and Eastern Clinical School, Alfred Hospital, Commercial Road, Melbourne, Victoria 3004, Australia. E-mail: helen.kelsall{at}med.monash.edu.au
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Abstract |
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Background Since the 1991 Gulf War, concerns have been voiced about the effects on the health of veterans of Gulf War related medical and chemical exposures.
Methods Our cross-sectional study compared 1424 male Australian Gulf War veterans and a randomly sampled military comparison group (n = 1548). A postal questionnaire asked about the presence of current neurological type symptoms, medically diagnosed neurological conditions, and medical and chemical exposures. A neurological examination was performed as part of a physical assessment.
Results Veterans have a higher prevalence of neurological type symptoms (ratio of means 1.4, 95% confidence interval (CI) 1.2–1.5). Although the odds ratio (OR) of lower limb neurological type symptoms and signs in veterans compared with the comparison group was increased (OR = 1.6, 95% CI 1.0–2.7), it was of borderline significance, and there was no difference between groups according to a Neuropathy Score based on neurological signs alone (ratio of means 1.1, 95% CI 0.9–1.3). The increased OR of neurological type symptoms and signs suggestive of a central nervous system disorder (OR = 1.8, 95% CI 1.0–3.1) was also of borderline significance. Veterans were not more likely to have self-reported medically diagnosed neurological conditions, or to have neurological type symptoms and signs suggestive of an anterior horn cell disorder (OR = 0.9, 95% CI 0.5–1.6). The total number of neurological type symptoms reported by veterans, but not the Neuropathy Score, was associated with Gulf War related exposures including immunizations and pyridostigmine bromide in dose–response relationships, anti-biological warfare tablets, solvents, pesticides, and insect repellents.
Conclusions This study shows increased reporting of neurological type symptoms in Gulf War veterans, but no evidence for increased neurological effects based on objective physical signs. There may be a number of factors, including information bias, relating to increased neurological type symptom reporting in veterans.
Keywords Gulf War veterans, nervous system diseases, chemical exposure, medical exposure, pyridostigmine bromide, immunizations
Accepted 21 March 2005
Veterans of the 1991 Gulf War (veterans) from different countries have consistently been found to report more symptoms than their non-Gulf comparison groups,1–4 especially symptoms that are neuropsychological5 or neuromuscular1,2,6 in nature. Two recent studies have reported elevated rates of clinically confirmed amyotrophic lateral sclerosis (ALS).7,8 Other neurological conditions, based on self-report1,2 or symptom-based definitions,3 are also reported more commonly. Recently, it has been reported that veterans have an increased risk of peripheral neuropathy9,10 although this has not been a consistent finding.11–15
It is of interest to see whether these adverse neurological outcomes are related to exposure to medications and chemicals during the Gulf War,16,17 such as pyridostigmine bromide (PB), immunizations, solvents, insect repellents containing N,N-diethyl-meta-toluamide (DEET), and pesticides including organophosphate insecticides, either singly or in combination. PB is a reversible acetylcholinesterase inhibitor that was used for nerve agent prophylaxis. It is one of the quaternary ammonium anticholinesterase agents that is prevented from entering the central nervous system (CNS) by the blood brain barrier.18 It has been postulated that organophosphate insecticides, nerve agent exposure, or combinations of possible chemical exposures may work synergistically to produce neurological effects,16 based on evidence from animal studies.19,20 Concurrent exposure to PB, DEET, and permethrin resulted in sensorimotor deficits and region-specific alterations in the cholinergic system,20 and concurrent exposure to stress may exacerbate neurotoxic effects,21 in rats. From this, it has been hypothesized that genetic polymorphism of enzymes such as paraoxonase/arylesterase 1 and butyrylcholinesterase may have increased the individual susceptibility of veterans to effects from exposure to neurotoxic chemicals that require these enzymes for detoxification.22,23 Serum paraoxonase activity has been observed to be lower in UK Gulf War veterans compared with non-Gulf comparison groups, although there was no difference between symptomatic and nonsymptomatic veteran groups.24 It has also been proposed that alterations in functioning neuronal mass in the basal ganglia and in central neurotransmitter production may, in part, explain the neurological effects found in veterans.25 The evidence is not conclusive in this field of study in humans, and methodological problems have been acknowledged.26 In particular, previous cross-sectional studies investigating neurological health of veterans have generally relied on self-reported health outcomes or lacked an adequate military comparison group.
Australia deployed 1871 defence personnel to the Gulf area as part of a larger multinational response to the invasion of Kuwait by Iraq on August 2, 1990. The majority of Australian Defence Force (ADF) personnel were naval personnel deployed on frigates, destroyers, or supply ships. Other ADF personnel included medical and nursing staff, mine clearance divers, intelligence officers, linguists, and weapons inspectors. Some ADF personnel were deployed with US and British forces. Smaller numbers of Royal Australian Air Force supplied transport and logistic support, but did not fly combat missions. A health risk assessment is undertaken for ADF deployments. Medical and preventive health measures for ADF personnel deployed to the Gulf War included immunizations, PB, anti-biological warfare, and anti-malarial tablets, personal insect repellents (varieties of which may have contained DEET), and pesticides.
We aimed to investigate whether Australian Gulf War veterans (veterans) had a higher prevalence of symptoms and signs suggestive of peripheral neuropathy (termed neurological type symptoms and signs in this manuscript for brevity), medically diagnosed neurological conditions, or combinations of neurological signs and symptoms suggestive of myopathy, anterior horn cell disease, CNS disorder or epilepsy than a randomly sampled, non-Gulf-War veteran, military comparison group. We also investigated whether veterans who received immunizations, took medications such as PB and anti-biological warfare tablets, or were exposed to chemicals such as solvents and pesticides, had more neurological type symptoms or signs than veterans who were not exposed.
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Methods |
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Subjects
The study population was the entire cohort of 1871 Australian veterans (1833 males, 38 females) who had served in the Gulf region during the period from August 2, 1990 to September 4, 1991. A comparison group of 2924 subjects (2850 males, 74 females) was randomly selected from 26 411 ADF personnel who were in operational units at the time of the Gulf War, but were not deployed to that conflict. The comparison group was frequency matched to the veteran group by sex, service type (navy, army, air force), and 3 year age bands. The study was conducted from August 2000 to April 2002. Subjects were recruited via mailed invitation with two further mailings and follow-up phone contact for non-responders.
Overall, 1808 eligible veterans (not including persons deceased or overseas and unavailable for the medical assessment) and 2796 eligible comparison group, 1456 (80.5%) veterans and 1588 (56.8%) comparison group subjects participated.
Owing to small numbers of female Gulf War veterans, analyses were limited to males. The study groups consisted of 1424 male Gulf War veterans (1232 navy, 87 army, 105 air force) who completed a postal questionnaire, of whom 1382 undertook the neurological examination, and 1548 male comparison group subjects (1123 navy, 172 army, 253 air force) who completed a postal questionnaire, of whom 1376 undertook the neurological examination. Participating veterans were slightly younger, more likely to have served in the navy, less highly ranked and less likely to have tertiary education, i.e. an undergraduate or post-graduate degree than comparison group subjects. Further details of the recruitment, demographic characteristics and smoking status, and the general health symptoms and medical conditions reported by, the study groups are provided by Ikin et al.27 and Kelsall et al.28,29
The Human Research Ethics Committees of Monash University, Department of Veterans' Affairs and the Department of Defence approved the study.
Data collection
Participants completed a self-administered postal questionnaire, which included questions about demographics, military service, 17 neurological type symptoms that may have been experienced in the past month, 63 recent general (including neurological) symptoms, medically diagnosed or treated conditions including the year first diagnosed, medical and chemical exposures including solvents, pesticides, insect repellents and Gulf War immunizations, PB, anti-malarial and anti-biological warfare tablets, the Alcohol Use Disorders Identification Test (AUDIT),30 and the 12 item version of the Short Form Health Survey (SF-12) version 1.31
Veterans were asked about the duration and quantity of PB, anti-malarial or anti-biological warfare tablets taken, and were asked to refer to their vaccination booklet, if available, for details about the total number, timing in relation to deployment, and time period over which they received immunizations.
Participants undertook a health assessment at one of 10 medical clinics located around Australia. This included a standardized neurological examination conducted by doctors, not neurologists, especially trained for the study and blinded to the participants' Gulf War status. The doctors also asked about each medically diagnosed or treated neurological condition reported in the postal questionnaire and classified the likelihood of diagnosis as ‘non-medical’, ‘unlikely’, ‘possible’, or ‘probable’. This was done to improve the accuracy of classification of the self-reported medical diagnoses.
Definitions of possible neurological disorders
We used combinations of neurological type symptoms and signs to define possible neurological disorders (Table 1). Where suitable, some neurological type symptoms suggestive of peripheral neuropathy have been incorporated into the other neurological definitions, such as one or more symptoms of muscle weakness into the definition of symptoms and signs suggestive of a CNS disorder. We also used a Neuropathy Score modified from the Mayo Clinic Neuropathy Impairment Score,32–34 a global score of muscle weakness and reflex and sensory abnormalities suggestive of neuropathy, based solely on signs elicited at a neurological examination. The Neuropathy Score was obtained by adding subscores for cranial nerve, muscle weakness, reflex and sensation abnormalities for the right and left sides of the body and combining them into a score for each person.
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Statistical analysis
Statistical analyses were performed using Stata version 7.0.35 Associations between deployment to the Gulf War and the presence of neurological type symptoms and other defined outcomes, adjusting for potential confounding factors, were assessed using logistic regression36 and reported as adjusted prevalence OR with 95% CIs. The possible confounding factors were chosen a priori and consisted of a core set (age, rank, service type, marital status, and education) as well as factors known to increase the risk of neurological disease (diabetes and excessive alcohol use). Differences in the total number of neurological type symptoms and the Neuropathy Score between the veterans and comparison group, adjusting for possible confounding factors, were obtained by negative binomial regression, which is a statistical technique applicable when outcomes involve counts (which are typically not normally distributed), and allows for greater dispersion of counted values than does a Poisson regression.37,38 The measure of effect that is produced from negative binomial regression is the ratio of the mean counts across the two groups being compared. Likelihood ratio tests36 were performed to investigate homogeneity of the effects of study group across categories of age, rank, and service type for the total number of neurological type symptoms and the Neuropathy Score. These tests were performed using interaction terms added to the regression models. The exposures to be assessed in relation to health outcomes were determined a priori. Dose–response trends were computed using the number of immunizations as a linear variable with trends reported per unit increase, and the number of PB tablets taken as a categorical variable with trends reported per category (none, 1–80, 81–180, >180 tablets) increase. Other exposures were considered as binary covariates in the regressions. The values of the unadjusted and the adjusted ORs and ratio of means were found to be highly similar, and so only the adjusted results are reported.
To investigate the possible effects of participation bias on our results, we collected brief demographic and SF-1231 data from a telephone survey of non-participants. Study participants, who completed the postal questionnaire, also completed the SF-12. A prediction model was used to compute an age-, rank- and service-adjusted OR for the relative health outcome of veterans vs comparison group subjects for having any neurological type symptoms as if the study had achieved full participation. The predicted ‘full participation’ adjusted ORs were averaged over 100 replications of the analyses.27
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Results |
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Table 2 shows that more veterans reported at least one neurological type symptom than the comparison group subjects, and a greater number reported all individual neurological type symptoms, with statistically significant differences for almost all neurological type symptoms reported in the past month. Furthermore, more veterans reported at least one symptom of muscle weakness, sensory disturbance, and autonomic dysfunction than did the comparison group. The total number of neurological type symptoms reported by veterans [mean 1.7 (SD 2.5), median 1] was significantly higher than that reported in the comparison group [mean 1.2 (SD 2.0), median 0, adjusted ratio of means 1.4, 95% CI 1.2–1.5]. This increase did not vary with age, service type and rank (all interaction P-values >0.37, data not shown). Adjustment for smoking (categorized as 0, <10, 10–20, >20 pack years), in addition to other possible confounding factors, made negligible differences to the resulting adjusted ORs or adjusted ratios of means in these or the following analyses (data not shown).
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Peripheral neuropathies tend to affect the lower limbs before the upper limbs, and people often report symptoms before signs are detectable on physical examination. Therefore, we used four operational definitions of increasing specificity to define neurological type symptoms and signs, as well as the Neuropathy Score. Veterans generally reported more neurological type symptoms and signs according to these operational definitions (Table 3). The exception to this was ‘more severe lower limb neurological type symptoms and signs’, where the numbers of defined cases were too small to draw meaningful conclusions. The increased OR of lower limb neurological type symptoms and signs in veterans compared with the comparison group was of borderline significance. The Neuropathy Score was similar in the veteran and comparison groups [mean 2.0 (4.3), median 0 vs mean 2.0 (4.7), median 0, adjusted ratio of means 1.1, 95% CI 0.9–1.3], and this overall result did not differ across subgroups of age, service type, and rank (all interaction P-values >0.45, data not shown). Similar proportions of veterans (65.2%) and comparison group (66.4%) subjects had a Neuropathy Score of zero.
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Table 4 shows the proportions of the veterans and comparison group who reported medically diagnosed or treated neurological conditions that had first been diagnosed since the Gulf War. The results were similar and no important differences were found. When the analysis was confined to conditions that had been rated as a ‘possible’ or ‘probable’ diagnosis by the examining doctors, the results were very similar.
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Two veterans and one comparison group subject reported medically diagnosed or treated motor neurone disease (MND) (Table 4). Given recent reports of increased MND in Gulf War veterans in overseas studies,7,8,39 we asked a neurologist, who was blinded to the participants' Gulf War status, to review the medical information from the postal questionnaire and medical assessment for these three subjects. The neurologist confirmed that the findings were consistent with MND in one veteran and not in the other. The subject reporting MND from the comparison group was found to have a compressive cervical myelopathy due to spondylosis and not MND. Table 4 also shows that a similar proportion of veteran and comparison group subjects had symptoms and signs suggestive of a disorder of anterior horn cells such as MND. Our definition correctly did not identify those two subjects whose self-reported MND was not confirmed by the above neurological review as having symptoms and signs suggestive of a disorder of anterior horn cells. Our definition excluded the veteran with MND, because of self-reported sensory symptoms (although sensation was normal on examination).
The increased OR of symptoms and signs suggestive of a CNS disorder in veterans compared with the comparison group was of borderline significance. Similar proportions of veterans and comparison group subjects had symptoms and signs suggestive of myopathy and of epilepsy, although the prevalences were small and this limited the power of the study to detect differences and to identify associations with Gulf War service (Table 4).
Medical and chemical exposures
Similar proportions of veterans and comparison group subjects reported exposure to pesticides (19.2% vs 15.9%) and solvents (73.9% vs 67.7%) during their entire military career, and exposure to pesticides (8.9% vs 9.8%) and solvents (30.0% vs 33.4%) during civilian jobs held for 
6 months. Therefore, such non-Gulf-War exposures were unlikely to confound any of the following results.
In relation to their Gulf War deployment, 1298 (91.6%) veterans reported receiving immunizations, including 342 (24.1%) who reported that they did not know how many immunizations they had received, and 119 (8.4%) veterans reported receiving none. Of 1113 veterans (for whom sufficient data was available for calculation), 151 (13.6%) were defined as having received a cluster of immunizations, that is, more than five immunizations within a period of a week or less. Some veterans were also uncertain about other medical exposures, and reported that they did not know whether they had taken PB, anti-biological warfare or anti-malarial tablets (Table 5 footnote).
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The total number of neurological type symptoms was associated with several Gulf War exposures including having taken PB and anti-biological warfare tablets, and using solvents, pesticides, and insect repellents during the Gulf War; but not with some other exposures such as having received any immunizations or a cluster of immunizations (Table 5). Increasing number of immunizations and increasing number of PB tablets received were associated with total number of neurological type symptoms in a dose–response relationship. The pattern of the relation between exposures and having any neurological type symptoms (data not shown) was similar to that observed for the total number of neurological type symptoms. The Neuropathy Score was not associated with any of the exposures examined.
Investigation of possible effects of participation bias
The telephone survey for non-participants, upon which part of the prediction model for assessing possible participation bias was based, was completed by approximately one-quarter (n = 411) of all study non-participants. The prediction model assumed that the telephone respondents' answers were representative of those of the remainder of the non-participants.
The predicted ‘full participation’ age-adjusted, rank-adjusted and service-adjusted prevalence OR of having any neurological type symptom between veteran and comparison group subjects was 1.36, which is only marginally lower than the corresponding OR of 1.42 observed for participants.
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Discussion |
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We found increased reporting of neurological type symptoms by Gulf War veterans, but no differences in reporting of medically diagnosed neurological conditions. We also found no convincing evidence for increased neurological effects based on combinations of neurological type symptoms and signs or on signs alone in Gulf War veterans when compared with the comparison group.
There has been limited study of peripheral neuropathy in previous Gulf War epidemiological works with which to compare our results. Cherry et al.6 found that 12.5% of the UK Gulf War veterans reported neuropathic symptoms compared with 6.8% of the non-Gulf comparison group. Our association, also based on symptoms, was not as strong as this. Jamal et al.10 found that both the neurological symptom score and the mean clinical signs score of 14 veterans with unexplained illnesses were increased compared with that of 13 civilian controls. However, they used small numbers of participants, a highly selected veteran sample and civilian controls for comparison, which makes meaningful interpretation difficult.
Our finding of increased neurological type symptom reporting by veterans, but no difference between study groups in the Neuropathy Score, is in general agreement with a recent study of US veterans;15 which found increased neuropathic symptom reporting in veterans, but no differences in prevalence of distal symmetric polyneuropathy between veterans and a non-deployed comparison group assessed by neurological physical examination or electrophysiology or by the methods combined. In addition, the US study reported a relation between the two objective methods of neurological assessment; veterans who had abnormal peripheral nerve conduction studies were found to be 3.89 times more likely to have distal symmetric polyneuropathy found on neurological physical examination.15 In other studies that used objective neurological testing, findings have varied. Five symptomatic veterans had some evidence of mild sensorimotor deficits in peripheral nerve function on nerve conduction studies, but electromyography was normal.9 In addition, another study found a small but statistically significant elevated threshold to cold sensation and differences in two other sensory nerve conduction tests comparing selected veterans and civilian controls.10 No objective abnormalities of neuromuscular disease were found in other studies of veterans with neuropathic11,13 or neuromuscular symptoms,12,40 although some veterans were found to have carpal tunnel syndrome,11,13 ulnar neuropathy,11,12 or increased lactate production during subanaerobic exercise.40 The research in this field remains inconclusive, and acknowledged methodological limitations include small sample sizes, use of highly selected samples or self-referred veterans from registry populations, lack of comparison groups or comparison with civilian controls, possible participation bias11,15,26 and concerns regarding the inclusion criteria used to define cases.17
In our study we used a combination of symptoms and signs in defining a possible disorder of anterior horn cells such as ALS, the most common form of MND. Two recently published studies that used active and passive ascertainment of ALS cases, confirmed by medical record or telephone or personal interview or both, found an approximately 2-fold significantly increased risk of ALS for US veterans overall7 and for US veterans diagnosed <45 years.8 Haley8 attributes the increased risk of ALS in younger veterans to an environmental trigger, and predicts that the peak has not yet been reached. On the basis of such findings,7 the US Department of Veterans Affairs has accepted ALS as a Gulf-War-related condition.39 We found no excess of symptoms and signs suggestive of a disorder of anterior horn cells to support the US finding, but we had too few defined cases to draw meaningful conclusions at this stage.
We found no important differences in reported medically diagnosed neurological conditions in veterans compared with the comparison group. Our analysis of the likelihood of diagnosis of self-reported neurological conditions, based on possible or probable diagnosis, suggests that veterans do not appear to be over reporting medically diagnosed or treated neurological conditions that were first diagnosed since the Gulf War compared with the comparison group. More veterans and comparison group subjects had symptoms and signs suggestive of neurological conditions such as anterior horn cell disease or CNS disorder than reported medically diagnosed or treated conditions. Therefore, it is possible that subjects in both study groups may have neurological conditions that have not yet been diagnosed or come to medical attention.
The reporting of neurological type symptoms, but not the Neuropathy Score, was associated with increasing numbers of immunizations received and PB tablets taken, and with taking anti-biological warfare tablets and using solvents, pesticides, and insect repellents. The lack of any association between the Neuropathy Score, defined solely on the basis of neurological signs, and medical and chemical exposures suggests that other factors such as information bias, including recall bias, need to be considered when attempting to explain these associations.
One strength of our study is the use of a military comparison group to whom the same definitions were applied, as this has not always occurred in previous studies. In addition, we were able to look at levels of reported chemical exposures in each participant's military career and civilian jobs. These were similar in both study groups, suggesting that they do not explain the differences between study groups.
There are some limitations to our findings for neurological health outcomes. The neurological type symptom questionnaire was not a validated questionnaire. It did not include qualifying questions around the duration of symptoms or differential causes. Although the neurological type symptom questionnaire and the definitions have face validity, they have not been validated in clinical practice. Neurological signs may not always be present even when symptoms and other features of the clinical history strongly indicate that a neurological disorder is present. The process of defining neurological outcomes used in our study, based on symptoms and signs or signs alone (such as in the Neuropathy Score), was not intended to be diagnostic. In our study populations the prevalence of true neurological disorders is likely to be fairly low and therefore a positive finding according to our definitions should be interpreted cautiously, in terms of their ability to predict true neurological disease. Further evaluation, such as an assessment by a neurologist or investigations such as electromyography or magnetic resonance imaging (MRI), would be required to determine whether the combinations of symptoms and physical signs are really related to pathology affecting the peripheral or CNS. Exposure assessment was based on self-report. The use of preventive health medication and measures may have varied between individuals, ships, and units depending on their perceived risk of exposure and self-compliance with medication. For example, the recommended PB dose of 30 mg eight-hourly before and for the duration of the period of exposure, was to be commenced on order of the Commanding Officer, based on medical advice. DEET-based insect repellent would probably have been issued to any ADF personnel going on shore in the Gulf region, but were probably not required or used at sea. Veterans' uncertainty in relation to their medical exposures could have influenced our results. There are several reasons for this uncertainty, including the time that has elapsed since the Gulf War and poor record keeping at the time of the Gulf War. This aspect of exposure assessment highlights the importance of medical record keeping in the defence forces. The prevalences of some defined outcomes were small and this limited the power of the study to detect differences and to identify associations with Gulf War service. Finally, although we did not find evidence of differential effects of Gulf War deployment across subgroups of rank, service, or age, our ability to detect small differential effects was limited, especially for subgroups of limited size such as non-Navy service.
Despite a rigorous contact and recruitment strategy, the comparison group participation rate was lower than that of the veteran group. Our veteran group participation rate was relatively high and the comparison group participation rate was comparable with that of other major postal surveys of veterans,1,2,4,41 and highlights the difficulties faced by researchers in contacting and recruiting young, highly mobile, military and ex-military populations. Our formal evaluation of possible participation bias suggests that this is unlikely to fully explain the differences (or lack thereof) that we found between our study groups. In addition, we adjusted for possible confounding factors such as age, rank, service type, marital status, education and smoking, as well as diabetes and excessive alcohol use that are known to increase the risk of neurological disease. To minimize any interviewer bias, data were collected in the same way using the same data collection forms for veteran and comparison group subjects, and examining doctors were blinded to participants' Gulf War status.
There may be a number of explanations for the observed increase in neurological type symptoms reported by veterans over what was reported by a comparable group of military personnel. The increase may really reflect a greater level of mild neurological effects in veterans. Alternatively, the increase in neurological type symptom reporting may be owing to information bias including recall bias. Veterans may be susceptible to publicity about ‘Gulf War problems’, and if so may be more likely to self-report neurological type symptoms in the past month. Recall bias may have occurred, as those who experienced symptoms may be more likely to report exposures.42 Wessely et al.43 found that worsening health perception (though not physical health or psychological morbidity) in UK veterans over time was associated with increasing new reporting of exposures. Participant awareness of the study's purpose may have exacerbated the possible effects of response frame,44 and veterans may have tended towards a response set of how veterans are ‘expected’ to appear. The increase in reported neurological type symptoms may also be part of the increased general ill health in veterans based on increased reporting of all general health symptoms and of symptom-based medical conditions;29,41,45 and with the increased reporting of multiple46 and sometimes unexplained47 symptoms following deployment to war,47 something that is not generally well understood.45 Post-combat syndromes over the past 100 years have, however, been characterized by a general shift from debility type symptoms to psychological or cognitive symptoms with a range of associated somatic symptoms.48
These possible biases should have had less of an effect on neurological health outcomes that we defined using combinations of symptoms and physical signs, and no effect on the Neuropathy Score that was defined solely by physical signs.
In conclusion, our study demonstrates increased reporting of neurological type symptoms by Australian Gulf War veterans, but no evidence for increased neurological effects based on objective physical signs. The relation with Gulf War exposures followed a similar pattern; associations with medical and chemical exposures were found only for neurological type symptoms and not for objective physical signs. There may be several factors contributing to increased reporting of neurological type symptoms. While this may indicate mild neurological effects in Gulf War veterans, information bias including recall bias is also another plausible explanation. Many of the conclusions of other epidemiological studies of veterans' neurological health have been based solely on self-reported findings. Our study emphasizes the importance of including objective physical signs in the future assessment of veterans.
KEY MESSAGES
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Acknowledgments |
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The study was funded by the Australian Government—Department of Veterans' Affairs. This study was overseen by a Scientific Advisory Committee and by a veterans' Consultative Forum, and we are grateful to members for their contributions and support. We acknowledge the contribution of Health Services Australia who conducted the medical assessments. We are grateful to Dr Wendyl D'Souza, neurologist, for his advice on, and training of doctors for, the standardized neurological examination performed in the study. We thank Dr Keith Horsley, Dr Warren Harrex, Mr Bob Connolly and his contact and recruitment team at the Department of Veterans' Affairs, Canberra. Finally, we thank the Gulf War veterans and members of the comparison group for the time and effort they made to participate in the study.
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References |
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