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Life expectancy standardized mortality ratios and causes of death in six rheumatic diseases in Hong Kong China.

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Vol. 63, No. 5, May 2011, pp 1182–1189
DOI 10.1002/art.30277
© 2011, American College of Rheumatology
Life Expectancy, Standardized Mortality Ratios, and Causes of
Death in Six Rheumatic Diseases in Hong Kong, China
C. C. Mok,1 C. L. Kwok,2 L. Y. Ho,1 P. T. Chan,1 and S. F. Yip2
Objective. To examine the life expectancy, standardized mortality ratios (SMRs), and causes of death
in 6 groups of patients from Hong Kong with different
rheumatic diseases.
Methods. Patients with a diagnosis of systemic
lupus erythematosus (SLE), rheumatoid arthritis (RA),
ankylosing spondylitis (AS), psoriatic arthritis (PsA),
systemic vasculitis (SV), or systemic sclerosis (SSc)
registered in 37 public hospitals between 1999 and 2008
were identified in the hospital registry. SMRs were
calculated by comparing the mortality rate in patients
with each disease with that in the general population.
Life expectancy was calculated by abridged life-table
analysis, and the causes of death were compared.
Results. In 2008, data on 8,367 RA, 5,243 SLE,
2,154 AS, 1,636 SV, 778 PsA, and 449 SSc patients were
available in our registry. The age- and sex-adjusted
SMRs were highest for SLE (5.25 [95% confidence
interval 4.79–5.70]), SSc (3.94 [95% confidence interval
3.20–4.68]), and SV (2.64 [95% confidence interval
2.36–2.93]). In female patients, the loss in life expectancy was greatest for SSc (34.1 years), SV (19.3 years),
and SLE (19.7 years). In male patients, the loss in life
expectancy was highest for SV (28.3 years), SLE (27
years), and SSc (16 years). There were 2,486 deaths
during the study period (1999–2008), and the principal
causes were infections (28%), cardiovascular complications (18%), cancer (16%), and disease activity (7%).
Infection was the leading cause of death in SLE, RA, AS,
and PsA, whereas deaths from disease-related activity
and cardiovascular complications were most frequent in
SSc. Cancer was the most common cause of death in SV.
Conclusion. Our findings indicate that patients
with SLE, RA, AS, PsA, SV, and SSc have increased
mortality rates and reduced life expectancy. SLE has the
highest adjusted SMR, and female SSc patients have the
greatest loss in life expectancy. Infection is the leading
cause of death, followed by cardiovascular complications and malignancies.
Rheumatic diseases are chronic multisystemic
medical illnesses that are associated with significant
mortality and morbidity. Organ dysfunction as a result
of disease involvement is a major cause of reduced
survival. Examples are renal failure in patients with
systemic lupus erythematosus (SLE) and systemic vasculitis (SV), pulmonary hypertension and interstitial lung
fibrosis causing cardiorespiratory failure in patients with
systemic sclerosis (SSc), and extraarticular complications, such as heart, lung, and renal diseases, in patients
with inflammatory arthritides, including rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic
arthritis (PsA). In addition to disease-related complications, adverse events related to treatment may aggravate
the risk of mortality. Immunosuppressive therapies for
various rheumatic diseases increase the incidence of
common bacterial and viral, as well as opportunistic,
infections and other long-term adverse effects, such as
liver fibrosis, malignancies, premature menopause, and
osteoporotic fractures.
Common to all of these rheumatic disorders is
chronic inflammation in the joints and the visceral
organs. Chronic inflammation is associated with the
persistent elevation of levels of proinflammatory markers, such as tumor necrosis factor ␣, interleukin-6 (IL-6),
and C-reactive protein (CRP), which are associated with
an increased risk of atherosclerosis and arterial thrombosis (1–3). The standardized incidence ratios of coronary heart disease and cerebrovascular disease (stroke)
are increased in patients with RA, SLE, AS, and PsA
(4–7), and these cardiovascular complications are major
causes of death, second to infection.
C. C. Mok, MD, FRCP, L. Y. Ho, MBChB, MRCP, P. T.
Chan, MBBS, MRCP: Tuen Mun Hospital, Hong Kong, China; 2C. L.
Kwok, BSc, S. F. Yip, PhD: University of Hong Kong, Hong Kong,
Address correspondence to C. C. Mok, MD, FRCP, Department of Medicine, Tuen Mun Hospital, Tsing Chung Koon Road, New
Territories, Hong Kong, China. E-mail:
Submitted for publication September 15, 2010; accepted in
revised form January 25, 2011.
The cumulative survival rate of an inception
cohort of patients who were diagnosed as having SLE
between 1991 and 2003 in our geographic area was 92%
5 years after disease onset and 83% 10 years after
disease onset (8). The unadjusted standardized mortality
ratio (SMR) for our local SLE patients in the year 2006
was estimated to be 2.2 (95% confidence interval [95%
CI] 0.7–6.7) (9). However, data on the life expectancy of
SLE patients and on mortality rates in other non-SLE
rheumatic diseases in our locality are unavailable. This
prompted the current study, which used the hospital
registry system and population census data to analyze
the life expectancy and SMRs for 6 diseases that are
commonly encountered in rheumatologic practice. The
causes of death in patients with these diseases were also
evaluated and compared.
Data source. Hong Kong is a small city situated in the
southern part of China. In the year 2009, it had an estimated
population of 7 million, 95% of whom were ethnic Chinese.
All citizens of Hong Kong are entitled to receive heavily
government-subsidized public medical services by paying a
nominal fee for medical consultations in hospitals and outpatient clinics. These medical services are provided by 37
hospitals run by the Hospital Authority, and they account for
⬎90% of the medical care provided in Hong Kong.
The numbers of patients with International Classification of Diseases, Ninth Revision (ICD-9), diagnostic codes for
SLE, RA, AS, PsA, SV, and SSc who were registered and
treated in 37 Hospital Authority hospitals between 1999 and
2008 were retrieved using the Clinical Data Analysis and
Reporting System (CDARS). This central system captures
data on both patients treated in outpatient clinics and inpatient
hospital admissions. Patients with these disease codes who died
during the specified period were identified using the same
system. The causes of death, which were recorded in the death
registry according to ICD-9 codes, were evaluated and compared across the 6 rheumatic diseases.
Determination of SMRs. The SMR was used to compare the mortality risk of patients with any of the 6 rheumatic
diseases to that of the general population of Hong Kong. SMR
and its asymptotic 95% CI were calculated as follows:
95% CI ⫽ SMR ⫺ 1.96 ⫻
, SMR ⫹ 1.96 ⫻
where O is the observed number of deaths in the study
population and E is the expected number of deaths (10).
For each of the 6 rheumatic diseases, the expected
number of deaths was calculated as the total number of
person-years contributed by the study population (i.e., patients
with that disease) multiplied by the mortality rate of the
general population. The age- and sex-adjusted SMRs were
calculated similarly, except that the expected number of deaths
was stratified by age and sex.
The size of the general population and the mortality
rate in the general population from 1999 to 2008 were obtained
from the Census and Statistics Department of the Hong Kong
government, which maintains population census data from the
years 1996, 2001, and 2006, with annual adjustments according
to birth, death, and immigration/emigration status. The mean
values of crude death rates over 10 years were used in the SMR
analysis described above.
Life expectancy analysis. Life expectancy for patients
with each of the 6 rheumatic diseases was estimated by
standard single-decrement life-table analysis as described by
Preston et al (11), using CDARS prevalence and death data
and Hong Kong population census data for 1999–2008. The
following assumptions were made in the construction of period
life tables for each sex and disease. First, the number of
patients and the number of deaths for each age group in a
given year were assumed to be independent of those in the
subsequent year, and second, deaths were assumed to be
symmetrically distributed in each age group. Under the first
assumption, the age-specific death rates mx could be estimated
by the maximum likelihood estimator for binomial distribution
parameter, given by
mx ⫽
d x1⫹d x2⫹· · · ⫹d xk
n x1 ⫹ n x2 ⫹ · · · ⫹n xk
where dkx is the number of deaths for age group x in the kth year
and nkx is the number of patients for age group x in the kth year
Although the second assumption might not be valid in
patients younger than 5 years old, this did not affect the results
of the life expectancy analysis, since no deaths were observed
in age groups 0–1 year and 1–4 years for patients with the 6
diseases that were studied.
Analysis of the causes of death. The principal causes of
death, as coded by the attending physician in the death registry
of the CDARS, were obtained for patients with the 6 diseases
who died between 1999 and 2008. These were grouped under
the following categories: infections, malignancies, cardiovascular and circulatory complications, cerebrovascular complications, gastrointestinal complications, hepatic complications,
respiratory causes (excluding infections), renal failure, trauma
and poisoning (including suicide), and related to rheumatic
disease activity but with unspecified exact causes.
Statistical analysis. Unless stated otherwise, values are
expressed as the mean ⫾ SD. Comparison of the frequencies
of deaths due to various causes across different rheumatic
diseases was performed by the chi-square test. P values less
than 0.05 (2-tailed) were considered significant. All statistical
analyses were performed using SPSS software, version 11.5 for
Windows XP.
Demographic characteristics of the patients. Table 1 shows the age, sex, and cumulative number of
patients with the diagnostic codes for each of the 6
rheumatic diseases captured by the CDARS at the
Table 1. Demographic characteristics of the patients with each rheumatic disease*
SLE (n ⫽ 5,243)
Women, no. (%)
Men, no. (%)
Ratio of female to
male patients
Age, mean ⫾ SD years
4,782 (91)
461 (9)
44.3 ⫾ 15.1
RA (n ⫽ 8,367)
6,657 (80)
1,710 (20)
56.4 ⫾ 17.0
AS (n ⫽ 2,154)
369 (17)
1,785 (83)
46.4 ⫾ 14.9
PsA (n ⫽ 778)
SSc (n ⫽ 449)
354 (46)
424 (54)
382 (85)
67 (15)
51.7 ⫾ 13.2
51.8 ⫾ 17.2
SV (n ⫽ 1,636)
1,021 (62)
615 (38)
51.4 ⫾ 19.4
* Data are for all living patients with records in the hospital registry at the beginning of 2008. SLE ⫽ systemic lupus erythematosus; RA ⫽
rheumatoid arthritis; AS ⫽ ankylosing spondylitis; PsA ⫽ psoriatic arthritis; SSc ⫽ systemic sclerosis; SV ⫽ systemic vasculitis.
beginning of 2008 (including all new and old patients
and living patients who were lost to followup). There
were 8,367 RA patients, 5,243 SLE patients, 2,154 AS
patients, 1,636 SV patients, 778 PsA patients, and 449
SSc patients. Their mean ages in 2008 were 44.3 years
for the SLE patients, 56.4 years for the RA patients, 46.4
years for the AS patients, 51.7 years for the PsA patients,
51.8 years for the SSc patients, and 51.4 years for the SV
patients. Patients with SLE, SSc, and RA were predominantly female, whereas patients with AS were predominantly male. There were slightly more women than men
with SV, and the sex distribution was roughly equal for
SMRs. The SMRs for the 6 rheumatic diseases
within the study period are shown in Table 2. The ageand sex-adjusted SMR was highest for SLE (5.25 [95%
CI 4.79–5.70]), followed by SSc (3.94 [95% CI 3.20–
4.68]), SV (2.64 [95% CI 2.36–2.93]), AS (1.87 [95% CI
1.61–2.13]), RA (1.68 [95% CI 1.59–1.77]), and PsA
(1.59 [95% CI 1.16–2.03]). For women, the age-adjusted
SMRs, in descending order, were as follows: SLE (5.59
[95% CI 5.07–6.12]), SSc (4.32 [95% CI 3.45–5.20]), SV
(2.66 [95% CI 2.27–3.05]), PsA (1.96 [95% CI 1.14–
2.77]), RA (1.72 [95% CI 1.61–1.82]), and AS (1.38 [95%
CI 0.74–2.02]). The corresponding values for men were
SLE (3.94 [95% CI 3.08–4.80]), SV (2.62 [95% CI
2.20–3.05]), SSc (2.59 [95% CI 1.32–3.87]), AS (1.94
[95% CI 1.65–2.22]), RA (1.59 [95% CI 1.42–1.76]), and
PsA (1.40 [95% CI 0.89–1.90]). The mortality rates for
patients with these rheumatic diseases were 59–425%
higher than those of the age- and sex-matched general
population. Of note, the adjusted SMR for SLE patients
was much higher than the unadjusted value (5.25 versus
2.63), indicating a much greater impact of mortality on
the younger population with this disease.
Results of life expectancy analysis. Figures 1 and
2 show the life expectancy curves for the 6 rheumatic
diseases, stratified according to sex, in comparison with
the life expectancy for the general population within the
same time period. The life expectancy curve for male
patients with PsA could not be plotted because of the
absence of deaths in the older age groups. For female
patients, the loss in life expectancy at the time of birth
compared with the general population was greatest for
patients with SSc (34.1 years), followed by SV (19.3
years), SLE (19.7 years), RA (6.9 years), PsA (6.5 years),
and AS (1.2 years). For male patients, the loss in life
expectancy was greatest for patients with SV (28.3
years), followed by SLE (27.0 years), SSc (16.0 years),
AS (7.0 years), and RA (5.2 years). The loss in life years
appeared to be greatest for younger patients (particularly patients with an age at onset of disease of younger
than 40 years).
Mortality rates and causes of death. Between
January 1999 and December 2008, there were 2,486
deaths (1,705 [69%] women). The distribution of deaths
for each of the underlying rheumatic diseases was 52%
RA, 21% SLE, 13% SV, 8% AS, 4% SSc, and 2% PsA.
Table 2. Standardized mortality ratios (SMRs) for the 6 rheumatic diseases within the study period*
Age-adjusted SMR (women)
Age-adjusted SMR (men)
Age- and sex-adjusted SMR
2.88 (2.61–3.15)
4.00 (3.13–4.87)
2.63 (2.41–2.86)
5.59 (5.07–6.12)
3.94 (3.08–4.80)
5.25 (4.79–5.70)
5.05 (4.73–5.37)
4.97 (4.43–5.50)
4.58 (4.33–4.83)
1.72 (1.61–1.82)
1.59 (1.42–1.76)
1.68 (1.59–1.77)
2.07 (1.11–3.03)
2.86 (2.44–3.28)
3.07 (2.64–3.50)
1.38 (0.74–2.02)
1.94 (1.65–2.22)
1.87 (1.61–2.13)
2.76 (1.61–3.91)
2.27 (1.44–3.10)
2.50 (1.81–3.19)
1.96 (1.14–2.77)
1.40 (0.89–1.90)
1.59 (1.16–2.03)
8.55 (6.82–10.28)
6.53 (3.33–9.73)
7.29 (5.93–8.65)
4.32 (3.45–5.20)
2.59 (1.32–3.87)
3.94 (3.20–4.68)
6.67 (5.70–7.65)
6.82 (5.70–7.93)
6.47 (5.77–7.18)
2.66 (2.27–3.05)
2.62 (2.20–3.05)
2.64 (2.36–2.93)
* Values are the SMR (95% confidence interval). See Table 1 for other definitions.
The mean ⫾ SD age at the time of death was 52.0 ⫾
17 years for SLE patients, 75.1 ⫾ 11.0 years for RA
patients, 68.6 ⫾ 17.0 years for SV patients, 69.5 ⫾ 11.4
years for AS patients, 67.2 ⫾ 13.6 years for PsA patients,
and 64.5 ⫾ 15.2 years for SSc patients.
Table 3 shows the causes of death according to
the ICD-9 codes recorded in the death registry. The principal causes of death were, in descending order of frequency, infections (28%), cardiovascular/cerebrovascular
complications (18%), cancer (16%), disease activity
(7%), renal failure (6%), pulmonary causes (6%), gastrointestinal and hepatic complications (4%), and accidents, injury, or poisoning (including suicide) (0.7%).
The cause of death was recorded as “other” in 4% of the
cases, and the cause of death was missing for 9%.
Infection was the leading cause of death in SLE,
Figure 2. Life expectancy curves for female patients (A) and male
patients (B) with ankylosing spondylitis (circles), psoriatic arthritis
(squares), or systemic vasculitis (triangles), as compared to the life
expectancy of the general population (diamonds) from 1999 to 2008.
The life expectancy curve for male patients with PsA could not be
plotted because of the absence of deaths in the older age groups.
RA, AS, and PsA, whereas disease-related and cardiovascular complications were the most frequent causes of
death in patients with SSc. Cancer was the most frequent
cause of death in patients with SV, while renal failure
was the most frequent cause of death in SLE and RA.
Figure 1. Life expectancy curves for female patients (A) and male
patients (B) with rheumatoid arthritis (circles), systemic lupus erythematosus (squares), or systemic sclerosis (triangles), as compared to
the life expectancy of the general population.
This is the first study to examine the mortality
statistics for different rheumatic disorders in a large
number of patients from the Hong Kong central hospital
registry. We demonstrated that the age- and sexadjusted mortality rates in patients with RA, SLE, AS,
PsA, SSc, and SV were significantly higher than those in
Table 3. Causes of death in the patients with rheumatic diseases (January 1999 to December 2008)*
Cause of death
(n ⫽ 514)
(n ⫽ 1,289)
(n ⫽ 197)
(n ⫽ 51)
(n ⫽ 110)
(n ⫽ 325)
(n ⫽ 2,486)
Soft tissue
Coronary heart disease
Heart failure
Pulmonary embolism
Pulmonary hypertension
Respiratory system
Obstructive airway disease
Pulmonary fibrosis
Renal failure
Disease activity
Unknown (missing data)
114 (22)
25 (5)
72 (14)
3 (0.6)
9 (1.8)
5 (1)
61 (12)
53 (10)
29 (6)
7 (1.4)
4 (0.8)
2 (0.4)
5 (1)
6 (1.2)
33 (6.4)
24 (4.7)
7 (1.4)
9 (1.8)
3 (0.6)
0 (0)
4 (0.8)
2 (0.4)
44 (9)
7 (1.4)
110 (21)
13 (2.5)
39 (8)
442 (34)
61 (5)
324 (25)
3 (0.2)
10 (0.8)
44 (3)
175 (14)
160 (12)
89 (7)
45 (3.5)
10 (0.8)
3 (0.2)
0 (0)
13 (1)
85 (6.6)
44 (3.4)
16 (1.2)
84 (6.5)
37 (3)
15 (1.2)
21 (1.6)
11 (0.9)
75 (6)
7 (0.5)
28 (2.2)
49 (4)
124 (10)
57 (29)
4 (2)
43 (22)
0 (0)
2 (1)
8 (4)
34 (17)
23 (12)
9 (4.6)
11 (5.6)
1 (0.5)
1 (0.5)
0 (0)
1 (0.5)
9 (4.6)
7 (3.6)
2 (1)
28 (14)
19 (10)
2 (1)
1 (0.5)
6 (3)
9 (4.6)
1 (0.5)
3 (2)
8 (4)
16 (8)
17 (33)
1 (2)
12 (24)
0 (0)
1 (2)
3 (6)
10 (20)
10 (20)
5 (10)
5 (10)
0 (0)
0 (0)
0 (0)
0 (0)
2 (4)
1 (2)
2 (4)
1 (2)
1 (2)
0 (0)
0 (0)
0 (0)
1 (2)
2 (4)
0 (0)
3 (6)
2 (4)
19 (17)
2 (2)
12 (11)
0 (0)
1 (1)
4 (4)
11 (10)
18 (16)
8 (7)
4 (4)
0 (0)
0 (0)
3 (3)
3 (3)
3 (3)
2 (2)
2 (2)
10 (9)
0 (0)
0 (0)
8 (7)
2 (2)
5 (4.5)
0 (0)
26 (24)
5 (4.5)
9 (8)
58 (18)
9 (3)
44 (14)
0 (0)
1 (0.3)
4 (1)
108 (33)
34 (10)
15 (5)
14 (4)
3 (1)
0 (0)
0 (0)
2 (0.6)
16 (5)
8 (2.5)
4 (1)
19 (6)
8 (2.5)
4 (1)
3 (1)
4 (1)
16 (5)
0 (0)
5 (1.5)
23 (7)
34 (10)
707 (28)
399 (16)
298 (12)
148 (6)
86 (3)
33 (1)
151 (6)
150 (6)
17 (0.7)
172 (7)
101 (4)
224 (9)
* Values are the number (%) of patients. See Table 1 for definitions.
the general population, by 0.6 to 4.3 times. The age- and
sex-adjusted SMR was highest for SLE (5.3), SSc (3.9),
and SV (2.6). For women, the loss in life expectancy at
birth was greatest for patients with SSc (34 years), SV
(19 years), and SLE (20 years). For men, the loss in life
expectancy was greatest for patients with SV (28 years),
SLE (27 years), and SSc (16 years). The most common
cause of death in all of the diseases studied was infection, followed by cardiovascular complications, malignancies, and uncontrolled disease activity. The loss in
life expectancy in patients with rheumatic diseases,
especially during the early years of life, is an important
issue because it causes a tremendous loss of economic
productivity in the community.
Although there have been a number of previous
studies of cumulative survival rates in patients with these
rheumatic diseases, not many studies focusing on ageadjusted mortality rates compared to the general population have been published. A PubMed search revealed
6 studies of SMRs in SLE patients, 12 in RA patients, 3
in PsA patients, 3 in SSc patients, and 3 in SV patients
(9,13–38). There was only one study on SMR in AS
patients, published in 1993 (39). The reported unad-
justed SMRs for RA and SLE ranged from 1.15 to 2.64
(17–28) and from 2.17 to 3.81 (9,13–17), respectively.
SSc had the highest SMR, with results ranging from 1.46
to 4.29 (33–35). The SMR of antineutrophil cytoplasmic
antibody–associated vasculitis ranged from 1.60 to 4.80
(36–38). The SMR of PsA patients was reported to be
1.62 in a cohort from the 1980s (32), but the SMR
determined in the past decade was reported to be
0.56–0.82, i.e., not higher than that of the general
population (30,31).
Table 4 summarizes the SMRs for different rheumatic diseases found in different studies. The SMRs for
the patients with SLE and SSc in the present study were
similar to those found in patients from most other
geographic areas. The SMR for patients with PsA in the
present study was 2.50, and the mortality rate was
significantly higher than that of the general population.
The SMRs for patients with RA, AS, and SV in the
present study were higher than those reported in the
literature. After adjustment for age and sex, the SMRs
for these 3 diseases ranged from 1.68 to 2.64. The
reasons for the discrepancies in the SMRs between
patients with RA, AS, and SV in the present study and
Table 4. Standardized mortality ratios for various rheumatic diseases determined in the past decade*
Author, year (ref.)
Present study
Hersh et al, 2010 (13)
Urowitz et al, 2008 (14)
Mok et al, 2008 (9)
No. of patients
Bernatsky et al, 2006 (15)
Chun and Bae, 2005 (16)
Bjornadal et al, 2004 (17)
Present study
434 (women)
Nakajima et al, 2010 (18)
Bergstrom et al, 2009 (19)
Young et al, 2007 (20)
Gonzalez, 2007 (21)
Sihvonen et al, 2004 (22)
Minaur et al, 2004 (23)
Thomas et al, 2003 (24)
Gabriel et al, 2003 (25)
Bjornadal et al, 2002 (26)
Gordon, 2001 (27)
Martinez et al, 2001 (28)
Chehata et al, 2001 (29)
Present study
Buckley et al, 2010 (30)
Ali et al, 2007 (31)
Wong et al, 1997 (32)
Present study
Hissaria et al, 2010 (33)
Ioannidis et al, 2005 (34)
Simeon et al, 2003 (35)
Present study
Lehtinen, 1993 (39)
Present study
Eriksson et al, 2009 (36)
Mohammad et al, 2009 (37)
Lane et al, 2005 (38)
63 (MPA/WG)
140 (MPA/WG/CSS)
SMR (95% CI)
Study period
Hong Kong,
Hong Kong,
2.63 (2.41–2.86)
2.5 (2.0–3.2)
3.81 (1.98–7.32)
2.17 (0.7–6.7)
2.4 (2.3–2.5)
3.02 (1.45–5.55)
3.63 (3.49–3.78)
Hong Kong,
4.58 (4.33–4.83)
1.46 to 1.90
1.15 (0.82–1.60)
1.27 (1.04–1.46)
1.35 (1.23–1.49)
2.64 (2.63–2.68)
2.13 (1.26–3.60)
2.07 (2.01–2.13)
1.97 (1.93–2.01)
1.27 (1.13–1.41)
2.03 (2.00–2.05)
1.30 (1.08–1.56)
1.65 (1.34–1.98)
Hong Kong,
2.50 (1.81–3.19)
0.82 (0.58–1.13)
0.56 (0.14–2.25)
1.62 (1.21–2.12)
Hong Kong,
7.29 (5.93–8.65)
1.46 (1.28–1.69)
1.5 to 7.2
4.29 (2.22–7.50)
Hong Kong,
3.07 (2.64–3.50)
Hong Kong,
6.47 (5.77–7.18)
1.6 (0.6–3.2)
2.77 (2.02–3.71)
4.8 (3.0–6.6)
* SMR ⫽ standardized mortality ratio; 95% CI ⫽ 95% confidence interval; MPA ⫽ microscopic polyangiitis; WG ⫽ Wegener’s granulomatosis;
CSS ⫽ Churg-Strauss syndrome (see Table 1 for other definitions).
those in previous studies are open to speculation.
Undercoding of RA and AS in the present study was
more likely to occur, since most patients are seen and
treated in the outpatient and day-ward setting. In the
present study, SV included all types of vasculitis as
judged by the attending physician, including paraneoplastic vasculitis. This might have caused a higher mor-
tality rate compared to those reported for antineutrophil
cytoplasmic antibody–associated vasculitis.
The causes of death in patients with the 6 rheumatic diseases investigated in this study were consistent
with those found in most previous studies (13–39).
Infections remained the most common immediate cause
of death. This was the result of immunomodulatory
therapies and the intrinsic immune aberrations of the
diseases themselves, causing an increased susceptibility
to invasion by microorganisms. Chronic inflammation
leading to persistent elevation of cytokine levels, which
is central to rheumatic disease activity, accelerates atherosclerosis in addition to traditional Framingham risk
factors. This explains the contribution of cardiovascular
and cerebrovascular complications as an important
cause of death in these diseases. Uncontrolled or refractory disease manifestations, particularly for some diseases such as SSc, SLE, and SV, lead to organ damage
and account for the decreased survival. On the other
hand, the long-term use of immunosuppressive agents
and defective immune surveillance increases the risk of
malignancies, which is another important cause of death
in rheumatic diseases.
Finally, it should be noted that while the factors
that contribute to mortality mentioned above are
disease-related, other factors, such as genetic background, environment, cultural beliefs, smoking, alcohol
abuse, education level, socioeconomic status, medical
and specialist referral system, delay in seeking medical
advice, availability of immunization programs, and compliance with treatment are also involved. This may also
explain the discrepancies in the mortality rates of the
same group of diseases observed in different geographic
The present study has some limitations. First, this
is a study derived from data obtained from a hospital
registry. Undercoding of the diagnoses among patients is
bound to occur, whereas the number of deaths recorded
in the registry is accurate and mandatory. This could
have led to an underestimation of the total number of
patients with the 6 diseases studied and subsequent
overestimation of the SMRs. Second, as with all registry
studies, the accuracy of the clinical diagnosis as judged
by the attending physician cannot be verified. Third,
we incorporated some assumptions into the calculation
of the mortality ratios and life expectancy, such as
uniform distribution of the number of deaths within the
age ranges. Finally, since the hospital registry data
management system only became available in the late
1990s, we did not have data on the trend of these
mortality statistics in the last decade compared to two
decades ago. Nevertheless, this is the first study to
describe the mortality statistics for various chronic rheumatic diseases in our geographic area. This serves as an
important reference for future survival analysis and
epidemiology surveys in our community and in the field
of rheumatology.
The authors would like to thank all of the rheumatologists and physicians working in public hospitals in Hong Kong
who contributed to the management of patients with rheumatic
diseases within the study period. We would also like to thank
the Hospital Authority headquarters staff members who are
responsible for maintaining the CDARS data system. Without
this system and their technical support, this study would not
have been successful.
All authors were involved in drafting the article or revising it
critically for important intellectual content, and all authors approved
the final version to be published. Dr. Mok had full access to all of the
data in the study and takes responsibility for the integrity of the data
and the accuracy of the data analysis.
Study conception and design. Mok, Kwok, Ho, Chan, Yip.
Acquisition of data. Mok, Kwok, Ho, Chan, Yip.
Analysis and interpretation of data. Mok, Kwok, Ho, Chan, Yip.
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