American Journal of Epidemiology
Copyright O 2000 by The Johns Hopkins University School of Hygiene and Public Health
All rights reserved
Vol. 151, No. 11
Printed/n USA.
Is Systemic Lupus Erythematosus, Amyotrophic Lateral Sclerosis, or
Fibromyalgia Associated with Persian Gulf War Service? An Examination of
Department of Defense Hospitalization Data
Tyler C. Smith, Gregory C. Gray, and James D. Knoke
Since the Persian Gulf War ended in 1991, veterans have reported diverse, unexplained symptoms. Some
have wondered if their development of systemic lupus erythematosus, amyotrophic lateral sclerosis, or
fibromyalgia might be related to Gulf War service. The authors used Cox proportional hazard modeling to
determine whether regular, active-duty service personnel deployed to the Persian Gulf War (n = 551,841) were
at increased risk of postwar hospitalization with the three conditions compared with nondeployed Gulf War era
service personnel (n = 1,478,704). All hospitalizations in Department of Defense facilities from October 1, 1988,
through July 31, 1997, were examined. With removal of personnel diagnosed with any of the three diseases
before August 1, 1991, and adjustment for multiple covariates, Gulf War veterans were not at increased risk of
postwar hospitalization due to systemic lupus erythematosus (risk ratio (RR) = 0.94, 95% confidence interval
(Cl): 0.65, 1.35). Because of the small number of cases and wide confidence limits, the data regarding
amyotrophic lateral sclerosis were inconclusive. Gulf War veterans were slightly at risk of postwar hospitalization
for fibromyalgia (RR = 1.23, 95% Cl: 1.05, 1.43); however, this risk difference was probably due to the Gulf War
veteran clinical evaluation program beginning in 1994. These data do not support Gulf War service and disease
associations. Am J Epidemiol 2000;151:1053-9.
amyotrophic lateral sclerosis; fibromyalgia; hospitalization; lupus erythematosus, systemic; military medicine;
Persian Gulf syndrome; veterans
The possibility of associations between Persian Gulf
War-related exposures and unusual postwar illnesses
has received considerable attention in both the popular
media and the medical literature (1-5). Since returning
from the war, many of the nearly 700,000 service personnel have reported a broad range of unexpected
symptoms (6-8). Although the causes of these symptoms remain unknown, strategies have been developed
to attempt to identify and define Gulf War-related illnesses. Recent epidemiologic studies have found no
unusual increases in birth defects (9, 10), hospitalization (11, 12), or mortality (13, 14) among Persian Gulf
War veterans when compared with nondeployed veterans of the same era. However, concern has been
expressed regarding the possibility of masking population risk differences for specific diagnoses when many
diagnoses are grouped together.
We sought to examine the association of Gulf War
service with three specific diseases that have gained
attention from veterans' groups, expert panels, and
researchers (3, 15-20): 1) systemic lupus erythematosus (SLE), a chronic autoimmune disease that causes
inflammation in various parts of the body, especially
the skin, joints, blood, and kidneys; 2) amyotrophic
lateral sclerosis (ALS), a motor neuron disease caused
by the gradual degeneration of nerve cells in the brain
and spinal cord; and 3) fibromyalgia, a chronic condition characterized by generalized aches, pains, and
stiffness in muscles and tendons.
Received for publication April 13,1999, and accepted for publication January 5, 2000.
Abbreviations: ALS, amyotrophic lateral sclerosis; CCEP,
Comprehensive Clinical Evaluation Program; Cl, confidence interval;
ICD-9, International Classification of Diseases, Ninth Revision; RR,
risk ratio; SLE, systemic lupus erythematosus.
From the Department of Defense Center for Deployment Health
Research, Naval Health Research Center, San Diego, CA.
Reprint requests to Tyler C. Smith, Naval Health Research Center,
Department of Defense Center for Deployment Health Research,
P.O. Box 85122, San Diego, CA 92186-5122 (smith ©nhrc.navy.mil).
MATERIALS AND METHODS
Population
The study population consisted of all regular activeduty military personnel who were either deployed to
the Persian Gulf War theater for one or more days during the Gulf War deployment period, August 8, 1990,
through July 31, 1991, or who were not deployed but
1053
1054
Smith et al.
were on active duty for at least part of the deployment
period (11).
The study focused on regular active-duty personnel
because their military hospitalization data are available
electronically and they are seldom hospitalized outside
of Department of Defense facilities (11, 21). Members
of the US Reserve and National Guard forces are generally not hospitalized in military facilities and therefore were not included in this investigation.
Deployment and demographic data were provided
by the Defense Manpower Data Center, Seaside,
California. Gulf War veteran demographic data
included age, sex, marital status, race (White, Black,
Hispanic, and "other"), service branch (Army, Navy,
Marine Corps, Air Force, and Coast Guard), service
type (active duty, National Guard, and US Reserve),
rank (enlisted, warrant officer, and commissioned officer), Persian Gulf War deployment status, and number
of days in the Persian Gulf arena (categorized by
approximate quartiles to 1-92 days, 93-149 days,
150-197 days, 198-572 days). These demographic
variables, evaluated at the time of the Gulf War, were
studied for possible associations with SLE, ALS, and
fibromyalgia.
Hospitalization data
Hospitalization data were captured from all
Department of Defense hospitals from October 1,
1988, through July 31, 1997, and included the date of
admission and up to eight individual discharge diagnoses. Diagnoses were coded according to the
International Classification of Diseases, Ninth
Revision (ICD-9) (22). All hospital admissions with an
ICD-9 code for SLE (710.0), ALS (335.20), or
fibromyalgia (729.1) were extracted. Hospitalization
data for the period of October 1,1988, through July 31,
1991, were scanned for one or more of these diagnoses. If a diagnosis was found, the subject was
removed from further analyses. Additionally, as in previous reports (11, 23, 24), a prewar hospitalization
covariate was created to denote an individual's hospitalization for any cause during the 12 months prior to
August 1, 1990.
Comprehensive Clinical Evaluation Program data
The Department of Defense Comprehensive Clinical
Evaluation Program (CCEP) is a voluntary registry for
active duty service members to evaluate, document,
diagnose, and treat conditions that may have arisen
subsequent to service in the Persian Gulf War arena (8,
25, 26). It was instituted in June 1994 to serve Gulf
War veterans who have remained on active duty,
retired from service, or who are currently serving in
the National Guard or the US Reserves. The program
consisted of a structured evaluation protocol, encompassing a comprehensive history and physical examination. If necessary, veterans were referred to specialists or referral hospitals for more advanced diagnostic
tests and treatment. Clinical diagnoses, symptoms, and
self-reported exposures were recorded for each participant. Active duty veterans were indicated as being
participants in the CCEP registry by match merging
CCEP participants with the study population.
Statistical analysis
Cox proportional hazard survival analysis modeling
was used to compare the hospitalization experience of
the Gulf War and nondeployed veterans. Subjects were
classified as having an event if they were hospitalized
in any Department of Defense hospital worldwide with
a diagnosis of SLE, ALS, or fibromyalgia and as censored otherwise. Follow-up time was calculated from
August 1, 1991, until hospitalization, separation from
service, or July 31, 1997, whichever occurred first. An
exploratory model analysis was first performed to
assess the significance of the demographic covariates
on the risk of the three diseases. Separate univariate
analyses for the three outcomes yielded consistent sets
of demographic covariates with p values of 0.10 or
below, which were included in all subsequent model
analyses.
The risk ratio and 95 percent confidence interval for
deployment status and the demographic covariates
were computed for the Cox models. Data management
and statistical calculations were performed using the
Statistical Analysis System (SAS Institute, Inc., Cary,
North Carolina) (27).
RESULTS
All Gulf War (n = 551,841) and nondeployed in =
1,478,704) veterans who had complete covariate data,
did not have a diagnosis with any of the three diseases
during the period of October 1, 1988, through July 31,
1991, and remained on active duty at the end of the
deployment period were included in the study population. The average length of service after July 31, 1991,
was 3.4 years (standard deviation, 2.3; range,
0.04-6.0) for Gulf War veterans and 3.8 years (standard deviation, 2.2; range, 0.07-6.0) for nondeployed
veterans.
Systemic lupus erythematosus
During the period of October 1, 1988, through July
31, 1991, 12 Gulf War veterans and 38 nondeployed
Am J Epidemiol
Vol. 151, No. 11, 2000
SLE, ALS, Fibromyalgia and the Gulf War
veterans were hospitalized with a diagnosis of SLE.
After these 50 personnel were removed from subsequent analyses, 36 Gulf War veterans and 160 nondeployed veterans were found to be hospitalized with SLE
during the 6 years of postwar study. Women had more
than 12 times the risk of men (table 1). The categories
of Hispanic and "other" were not appreciably different
from Whites; therefore, these three categories were
combined and classified as non-Blacks. Blacks were at
more than three times the risk of non-Blacks (table 1).
Increasing age was strongly associated with risk for
SLE hospitalization (table 1). Other demographic
covariates—branch of service, marital status, and
being hospitalized prior to the start of the Gulf War—
were not statistically significant and consequently
were not included in final analyses. Rank was not
included in the final analyses because of colinearity
with age. Deployment status was not associated with
SLE (risk ratio (RR) = 0.94, 95 percent confidence
interval (CI): 0.65, 1.35).
Separate models for Gulf War veterans and nondeployed veterans were examined to determine if interaction was present between the demographic variables
and deployment status; no appreciable interactions
were apparent. Gulf War veterans were not at
increased probability of hospitalization in comparison
with nondeployed veterans during the 6 years of follow-up (figure 1).
Amyotrophic lateral sclerosis
During the period of October 1, 1988, through July
31, 1991, one Gulf War veteran and three nondeTABLE 1. Adjusted risk ratios among regular active-duty
personnel for hospttallzatlon with systemic lupus
erythematosus In US Department of Defense hospitals,
August 1,1991, to July 31,1997
Total
no.
No. of
cases
Adjusted
RR*
95%
CI*
1,477,287
550,153
160
36
0.94
0.65, 1.35
Sex
Malet
Female
1,805,930
221,510
70
126
12.12
8.98, 16.36
Age (years)
2,027,440
196
1.04
1.02, 1.07
Race
Non-Blackt
Black
1,610,997
416,443
85
111
3.61
2.71,4.82
Characteristic
Gulf War veteran
Not
Yes
* RR, risk ratio from Cox proportional hazards model; CI,
confidence interval,
t Reference category.
Am J Epidemiol Vol. 151, No. 11, 2000
1055
.07
c
o
- 06
1 -05
S
I
o
.03
«
.02
.01
Gulf War
Nondeployed
0.00
Years From August 1,1991
FIGURE 1. Probability of hospitalization for systemic lupus erythematosus in Department of Defense hospitals during the period
August 1, 1991, through July 31, 1997. Gulf War veterans (n =
550,153) versus nondeployed veterans (n = 1,477,287).
ployed veterans were hospitalized with a diagnosis of
ALS. These personnel were removed from postwar
modeling. Because of the small number of subjects
hospitalized after the war with ALS (six Gulf War
veterans, 12 nondeployed veterans), not all demographic covariates were included in a single model
analysis with deployment status. Separate model
analyses were run for the different demographic
covariates to determine which ones were significant
influences on the risk of ALS and which categories of
different covariates could be combined. The result
was a manageable covariate load on the model with
age and deployment status as covariates. Branch of
service, marital status, race, sex, and prewar hospitalization were not statistically significant in the screening analyses and consequently were not included in
the final models. Rank was also removed from the
final models because of colinearity with age.
Increasing age was strongly associated with hospitalization risk. Deployment status was not significantly
associated with ALS (RR = 1.66, 95 percent CI:
0.62, 4.44).
Separate models for Gulf War veterans and nondeployed veterans were examined to determine if interaction was present between age and deployment status;
no appreciable interaction was apparent. The two
groups had the same probability of hospitalization for
ALS during the first 3.5 years of follow-up, August
1991 to January 1995. After this time point there were
no nondeployed cases to compare with the final two
deployed cases.
1056
Smith et al.
Fibromyalgia
During the period of October 1, 1988, through July
31, 1991, 150 Gulf War veterans and 339 nondeployed
veterans were hospitalized with a diagnosis of
fibromyalgia. These personnel were removed from
postwar modeling. During the 6 years of postwar
study, 239 Gulf War veterans and 621 nondeployed
veterans were hospitalized with fibromyalgia. Women
had more than three times the risk of men (table 2).
Increasing age was strongly associated with hospitalization risk. A person hospitalized prior to the start of
the Gulf War had 1.6 times the risk of hospitalization
with fibromyalgia. Army personnel had almost 3 times
the risk of Navy personnel. Marines and Air Force personnel had approximately 1.5 times the risk of Navy
personnel. The other demographic covariates—marital
status and race—were not statistically significant and
consequently were not included in the final models.
Rank was not included in the final model analyses
because of colinearity with age. Deployment status
was found to be associated with hospitalization for
fibromyalgia, with Gulf War veterans at 1.2 times the
risk of hospitalization (RR = 1.23, 95 percent CI:
1.05, 1.43) compared with nondeployed veterans.
Separate models for Gulf War veterans and nondeployed veterans were examined to determine if
interactions were present between the other covariates
TABLE 2. Adjusted risk ratios among regular active-duty
personnel for hospitalization with fibromyalgia In US
Department of Defense hospitals, August 1,1991, to July 31,
1997
Total
no.
Mo. of
1,478,186
550,529
621
239
1.23
1.05,1.43
Prewar
hospital Ization
Not
1,886,083
Yes
142,632
745
115
1.63
1.33,1.99
Sex
Malet
Female
1,807,064
221,651
607
253
3.28
2.82, 3.82
Age (years)
2,028,715
860
1.05
1.04, 1.06
Service
Navyt
Army
Marines
Air Force
600,727
716,702
196,643
514,643
141
446
47
226
2.75
1.35
1.61
2.28, 3.33
0.97,1.89
1.30, 1.98
Characteristic
Gulf War veteran
Not
Yes
* RR, risk ratio; CI, confidence interval,
t Reference category.
Actuated
RR*
and deployment status. No appreciable interactions
were detected. Gulf War and nondeployed veterans
had the same probability of hospitalization for
fibromyalgia during the first 3.5 years of follow-up
(figure 2). At this point there was a noticeable
increase for Gulf War veterans in the probability of
being hospitalized. This increase in the probability
was consistent with the inception of the Department
of Defense CCEP in June 1994. To investigate this
observation, we split the follow-up period into two
time periods, before and after the inception of the
CCEP. The model analysis of the time period before
the inception of the CCEP, August 1, 1991, through
June 30, 1994, showed no increased risk of hospitalization with fibromyalgia among Gulf War veterans
(RR = 0.92, 95 percent CI: 0.74, 1.13). The model
analysis of the time period after the inception of the
CCEP, June 30, 1994, through July 31, 1997, showed
almost twice the risk of fibromyalgia hospitalization
among Gulf War veterans (RR = 1.76, 95 percent CI:
1.39, 2.22).
A CCEP participant covariate was created and
added to the Cox model for the second time period to
see if that variable would account for some of the
variance in the model. The CCEP participants had
more than 26 times the risk of being hospitalized with
fibromyalgia than did nonparticipants (RR = 26.40,
95 percent CI: 18.62, 37.43). After the introduction of
the CCEP covariate, Gulf War veterans' risk
markedly declined (RR = 0.56, 95 percent CI: 0.41,
0.78).
95%
Gulf War
Nondeployed
Years From August 1,1991
FIGURE 2. Probability of hospitalization for fibromyalgia in
Department of Defense hospitals during the period August 1, 1991,
through July 31, 1997. Gulf War veterans (n = 550,529) versus nondeployed veterans {n = 1,478,186). CCEP, Comprehensive Clinical
Evaluation Program.
Am J Epidemiol Vol. 151, No. 11, 2000
SLE, ALS, Fibromyalgia and the Gulf War
DISCUSSION
It has been suggested that Gulf War veterans may be
suffering from SLE, ALS, and fibromyalgia due to war
exposures. Recognizing data limitations, our analyses
of the best available hospitalization data do not support
such deployment-disease associations. Our risk factor
findings were generally consistent with those in the
published literature.
Systemic lupus erythematosus
Our finding that women were at increased risk for
hospitalization with SLE is consistent with other
reports that show women to have 10-15 times the risk
of men (28). The finding that Blacks were at an
increased risk over other races is also consistent with
the literature (28, 29).
Amyotrophlc lateral sclerosis
Our finding that older personnel were at a greater
risk for acquiring ALS than were younger people is
consistent with published literature (30, 31). Despite
the very large number of study subjects, we detected
sparse ALS outcomes, and our analyses are limited in
statistical power to detect risk factor associations with
ALS hospitalizations. This is evident by the broad confidence interval around the Gulf War veterans/nondeployed veterans' adjusted postwar hospitalization risk
ratio (RR = 1.66, 95% CI: 0.62, 4.44). Assuming similar conditions, we found these data to be only adequate to detect a statistically significant risk ratio of
2.82. Interestingly, a recent medical chart review by
the Department of Veterans Affairs suggested that as
many as 28 Gulf War veterans may have developed
ALS after the war, suggesting an increased incidence
compared with civilian populations (32). Further studies of ALS among Gulf War veterans are being
planned.
Fibromyalgia
Much attention has been given to the diagnosis of
fibromyalgia among Gulf War veterans (5, 17, 33, 34).
Our finding of greater risk for females is consistent
with the literature (35, 36). The finding that the Army
and Air Force personnel were at a greater risk than
were the Navy and Marine Corps personnel may have
been a result of the increased CCEP hospitalizations
by Army and Air Force hospitals. The effect of age on
the outcome of fibromyalgia has not been previously
reported and may be an artifact.
Our analyses showed a slightly increased risk of
fibromyalgia hospitalization for Gulf War veterans
Am J Epidemiol Vol. 151, No. 11, 2000
1057
versus nondeployed veterans. Six years after the conflict ended, the cumulative probability of hospitalization for fibromyalgia was 0.00048 percent for nondeployed veterans and 0.00061 percent for the Gulf War
veterans (figure 2). This overall risk increase reflects a
sharp temporal increase in risk beginning around June
1994. An analysis of the time period August 1, 1991,
through June 30, 1994, showed no increase in risk for
Gulf War veterans. The analysis for the time period
June 30, 1994, through July 31, 1997, showed an
almost twofold increase in risk for Gulf War veterans.
In June 1994, a strategy of admitting some CCEP
participants at large Army and Air Force hospitals was
adopted. This may have been responsible for causing
an artificial increase in hospitalizations for fibromyalgia among Gulf War veterans. A recent report found a
similar trend for diagnoses associated with hospitalizations due to unexplained illnesses (23). That report
noted that several large Army and Air Force hospitals
created special wards for the hospitalization of CCEP
participants. These CCEP participants were admitted
for extensive clinical evaluations, sometimes for several days. The admission of CCEP participants was
discontinued in mid-1995, at which time the hospitalization curves for fibromyalgia again became nearly
parallel (figure 2).
Adding a CCEP participant covariate to the analysis
of the post-CCEP conception time period indicated
that participation in the CCEP was a strong independent risk factor for fibromyalgia. CCEP participants
had 26 times the risk of being hospitalized for
fibromyalgia compared with nonparticipants. Our
analysis suggests that the increase in hospitalizations
for fibromyalgia among Gulf War veterans may be due
to transient confounding by the strategy of hospitalizing CCEP participants for extensive evaluations during
the first year the program was in existence.
Data limitations
These analyses have a number of limitations. A key
limitation involves exposure classification. Gulf War
exposure status was defined as those persons deployed
to the Gulf War theater for one or more days during the
deployment period. This broad classification does not
account for specific exposures encountered during the
deployment. Unfortunately, good quality data for specific Gulf War exposures are not available (3, 15, 16).
We explored two surrogates for Gulf War exposure
data: time in theater (days) and possible exposure to
chemical munitions (three exposure categories) (37).
Studying only Gulf War veterans, we individually
examined these risk factors for associations with postwar hospitalizations with the three diseases (total of
six models). Neither time in theater nor possible expo-
1058
Smith et al.
sure to chemical munitions was important in predicting
the diseases (data not shown).
Our study is limited in ability to detect disease.
Ideally, before we compared the two cohorts, we
should have screened out all persons who had the diseases of interest prior to the war. We did so as best we
could by examining all available hospitalization data
back to October 1988. However, we recognize that we
may have missed personnel who developed these diseases before that time or who were treated as outpatients. No electronic outpatient morbidity data are
available until 1997. Additionally, our postwar hospitalization analyses would have detected only personnel
who were ill enough to be admitted to hospitals. Our
ascertainment of cases was further limited by departures from military service. Many personnel separated
during the period of follow-up: 59.9 percent of the
Gulf War veterans and 54.3 percent of the nondeployed veterans had separated by June 30,1996. As no
comprehensive national hospitalization databases are
available (12), we could not identify individuals hospitalized in nonmilitary hospitals.
Study strengths
This study's large population {n = 2,030,545) and
the availability of important demographic covariates
offer unusually high statistical power to detect differences between the two cohorts for SLE and fibromyalgia hospitalizations. We are confident that the available hospitalization data are nearly complete as
active-duty personnel are seldom hospitalized outside
of the Department of Defense system (11, 21).
Additionally, routine physical screening and frequent
physical fitness testing of military personnel
strengthen the probability of early detection of these
diseases with subsequent hospitalization for evaluation, as compared with similar studies of civilian personnel not so screened. Finally, in preparation for separation from military service, personnel receive
thorough medical screening and evaluations. They recognize the importance of reporting any symptoms or
illnesses as they may receive lifelong disability benefits if a disorder or disease is found to be service connected. This causes them to be rather thorough in their
reporting of symptoms and illness (21).
ACKNOWLEDGMENTS
This represents report no. 99-1, supported by the
Department of Defense/Health Affairs, under NMRDC
reimbursable - 6423. A preliminary report of these data was
presented at the Conference on Federally Sponsored Gulf
War Veterans' Illnesses Research in Pentagon City,
Maryland, June 17-19, 1998. This study was conducted in
accordance with Department of Defense and Department of
the Navy instructions.
The authors thank Michael A. Dove and Wayne F. Woo
from the Management Information Division, Defense
Manpower Data Center, Seaside, California, for providing
Gulf War veteran deployment data.
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