(Stroke. 2000;31:9.)
© 2000 American Heart Association, Inc.
Original Contributions |
From the Department of Epidemiology and Preventive Medicine, Institute of Internal Medicine, Siberian Branch of the Russian Academy of Medical Science (V.L.F., S.V.S., G.M.T., T.E.V., A.V.T., S.V.V., Y.P.N.), and Department of Neurology and Neurosurgery, Novosibirsk Medical University (V.L.F.), Novosibirsk, Russia.
| Abstract |
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MethodsThis is a prospective registry population-based study of all new cases of TIA and stroke in an overall population of 455 765 residents of Novosibirsk. All new TIA and stroke incident cases (whether inpatient or outpatient) that occurred during 19871988 and 19961997 study periods were recorded and analyzed. A 95% CI was estimated for all age- and sex-specific strata.
ResultsDuring the 2 study periods, a total of 211 patients with first TIA were registered in the population studied. The crude annual TIA incidence rate per 100 000 residents was 16 (95% CI, 8 to 33) in 19871988 and 29 (95% CI, 9 to 87) in 19961997; these rates standardized to the European population were 17 (95% CI, 8 to 34) and 27 (95% CI, 9 to 79), respectively. Eighty-three percent of TIAs occurred in the carotid arteries (rate, 48/100 000), 10% occurred in the vertebrobasilar territory (rate, 6/100 000), and 7% of cases had a TIA of uncertain distribution (rate, 2/100 000).
ConclusionsUnlike stroke incidence rate, the incidence rate of TIA in Novosibirsk is similar to that in other populations and constitutes approximately 10% of stroke incidence. For the last decade (19871997), there was a tendency, although statistically insignificant, toward increasing incidence rate of TIA in the population studied.
Key Words: epidemiology incidence stroke transient ischemic attack
| Introduction |
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| Subjects and Methods |
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Immediate notification of all new cases of TIA/stroke or alleged TIA and stroke came to the TIA and Stroke Registry Department (TSRD) of the study district on an ongoing basis by telephone from 8 AM to 6 PM on workdays. These notifications came from primary care physicians, neurologists, and inpatient and outpatient clinics. The completeness of the information was verified by research personnel of the TSRD, who weekly checked inpatient and outpatient clinic data, including all ambulance call registrations within and just outside the study district, hospital registrations, and hospital refusals (in the study district, TIA and stroke patients can be hospitalized or otherwise medically served only in specified clinics). On the basis of these overlapping sources of information, all new patients with TIA/stroke or suspected TIA/stroke were examined daily and interviewed by a specially trained neurologist (cerebrovascular disease expert) of the TSRD (S.V.S.) at home or at the hospital as soon as possible after the episode of TIA/stroke or alleged TIA/stroke became known to the TSRD. Additionally, 2 of the authors (V.L.F. and S.V.S.) reviewed all the medical records and placed patients into diagnostic categories according to the best information available.
The definitions of TIA and stroke were based on standardized criteria.12 TIA was diagnosed clinically in subjects with focal neurological symptoms relating to focal cerebral, brain stem, or retinal ischemia with abrupt onset and complete resolution within 24 hours (usually within minutes). Isolated diplopia, vertigo, focal symptoms associated with migraine, or other nonspecific symptoms were not considered TIA. TIA patients with focal motor or sensory symptoms affecting 1 side of the body or with aphasia/dysphasia, amaurosis fugax (retinal ischemia), or any combination of these symptoms were considered to have TIA in the carotid system. Those TIA patients who had motor and/or sensory symptoms on both sides of the body, a combination of unilateral motor/sensory symptoms with any brain stem symptoms (such as vertigo, diplopia, dysphagia, ataxia, or dysarthria), ataxia of gait, bilateral clumsiness of the arms and/or legs, diplopia, dysarthria, bilateral homonymous hemianopsia, or any combination of these symptoms were regarded as patients with vertebrobasilar TIA. Those TIA patients who had symptoms occurring in both carotid and vertebral distributions were considered to exhibit TIA symptoms of uncertain distribution.
Stroke was defined as rapidly developed signs of focal (or global) disturbance of cerebral function lasting >24 hours (unless interrupted by surgery or death), with no apparent nonvascular cause (this category included cerebral infarction, intracerebral hemorrhage, and subarachnoid hemorrhage); methods of stroke case ascertainment and criteria for diagnosis of stroke subtypes have been described elsewhere.13 14 These data had to be sufficiently well documented to ensure a high likelihood that a TIA or stroke had occurred. Only persons with definite diagnosis of first-ever-in-a-lifetime TIA or stroke were included in the analysis. In this study, TIA patients who had a history of stroke were excluded from the analysis.
The number of first-ever TIA and stroke cases was expressed as an annual rate per 100 000 of the population of the corresponding age and sex. Denominator age- and sex-specific person-years were estimated from all-union census data for Oktyabrsky and Leninsky districts of Novosibirsk in 1989 to calculate age- and sex-specific TIA incidence rates for 19871988 and 19961997. TIA incidence rates were computed with data pertaining to 2 different districts (Oktyabrsky and Leninsky districts of Novosibirsk). The data of 1 of the 2 districts (Oktyabrsky District) were available only for the survey of 19961997, while in the survey of 19871988 we used data derived from the 2 districts. For the purpose of comparison of TIA and stroke incidence rates, we used our stroke register data in Oktyabrsky District of Novosibirsk (the stroke register method has been described elsewhere).13 Age and sex adjustment of the incidence rates was done by a direct method with the European population as a standard.15 The difference in rates was assessed by comparison of the 95% CI, which was computed by the method described by McDonnell et al.16
| Results |
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75 years, stroke
incidence rates per 100 000 residents were 17, 375, 734, and 1875 in
19871988 and 15, 389, 1262, and 2236 in 19961997, respectively).
The overall age- and sex-adjusted incidence rate for acute
cerebrovascular events (TIA and stroke combined) was 211/100 000 in
19871988 (95% CI, 49 to 954) and 266/100 000 in 19961997 (95%
CI, 91 to 779).
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The ratio of age-adjusted TIA incidence rates of men to women was 1.1
in 19871988 and 0.9 in 19961997; for stroke cases at the same study
periods, these ratios were 1.2 and 1.0, respectively. However, in the
group aged 45 to 64 years, the overall TIA incidence rate in men
(59/100 000) was 26% higher than that in women (44/100 000). Of the
211 TIA events, 7% occurred in persons younger than 45 years, 32% in
the group aged 45 to 64 years, 14% in the group aged 65 to 74 years,
and 6% in persons aged
75 years. The corresponding figures for
strokes were 8%, 34%, 35%, and 23%. For the 10-year study period,
there was a statistically insignificant increase in the age- and
sex-adjusted incidence rates of TIA: 17/100 000 in 19871988 (95%
CI, 8 to 34) and 27/100 000 in 19961997 (95% CI, 9 to 79). Age-
and sex-adjusted stroke incidence rates increased from 195/100 000
(95% CI, 41 to 919) in 19871988 to 239/100 000 (95% CI, 81 to
700), but the increase was statistically insignificant. The ratio of
age- and sex-adjusted incidence rates of stroke to TIA for these study
periods also did not change significantly (12 in 19871988 and 9 in
19961997; overall for the entire study period, approximately 10). No
statistically significant difference in the mean age of patients with
TIA and stroke was noted: the mean age of TIA patients ranged from 39
to 89 years and in 19961997 was 62.3±11.4 years in men and
66.5±11.2 (±SD) years in women; the mean age of men and women with
stroke in 199214 was 63.1±12.8 and 66.3±12.7 (±SD)
years, respectively.
Of the 89 TIA cases in 19961997, 74 (83%) occurred in the carotid arteries, 9 (10%) occurred in the vertebrobasilar territory, and 6 cases (7%) had a TIA of uncertain distribution. The overall incidence rate of TIA in the carotid artery distribution was 48/100 000 (95% CI, 38 to 60) (in men, 38/100 000 [95% CI, 26 to 56]; in women, 55/100 000 [95% CI, 41 to 74]), 6/100 000 for vertebrobasilar distribution TIA (95% CI, 3 to 11) (in men, 6/100 000 [95% CI, 2 to 15]; in women, 6/100 000 [95% CI, 2 to 14]), and 2/100 000 for TIA of uncertain distribution (95% CI, 1 to 4) (in men, 3/100 000 [95% CI, 1 to 9]; in women, 1/100 000 [95% CI, 0 to 7]).
| Discussion |
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In comparison with other population-based epidemiological
studies,1 4 6 19 our data suggest that the incidence rate
of TIA for all ages in Novosibirsk in 19961997 (31/100 000 per
year), age- and sex-adjusted to the US white population in 1980, as
calculated for these studies by Brown and colleagues,4 is
similar to that in Oxfordshire, England, in 19811986 (36/100 000);
Söderhamn, Sweden, in 19751978 (33/100 000) and 19831986
(38/100 000); and Estonia, USSR, in 19701973 (37/100 000) but is
twice as low as that in Rochester, Minnesota, in 19851989
(68/100 000). Our data on the TIA incidence rate, age- and
sex-adjusted to the US white population in 1980, in Novosibirsk in
19871988 (18/100 000 per year) are similar to those for Hisayma,
Japan, in 19611982 (22/100 000).4 20 The overall TIA
incidence rate in Novosibirsk adjusted to the European population
(27/100 000; 95% CI, 9 to 79) is similar to that reported in a
population-based study in Spain (21/100 000; 95% CI, 12 to
30)7 and Italy (42/100 000; 95% CI, 33 to
54).5 In Dijon, France, the world-standardized incidence
of TIA over the 10-year period (19851994)2 varied from
8.4 to 29.2 cases per 100 000 residents per year in men and from 3.9
to 18.8 cases per 100 000 residents per year in women, but these
changes were not statistically significant. However, the mean age of
TIA patients in Novosibirsk (62 years in men and 66 years in women)
appears to be lower than that in some European
countries.1 5 7 Because of the small proportion of
population aged
65 years in Novosibirsk (7.5%), identification of a
small number of additional TIA or stroke cases would have markedly
altered the incidence rate. This resulted in very wide CIs obtained in
groups of the population aged 65 to 74 and
75 years. In contrast to
other population-based studies,1 4 5 7 TIA patients in
Novosibirsk aged >75 years constituted only 6% of all TIA patients.
This may reflect the fact that (1) elderly patients in Novosibirsk do
not seek medical attention as much as younger patients and/or (2)
transient cerebrovascular events in elderly patients are often
overlooked by general practitioners. Thus, there is a
possibility that the true TIA incidence rate in Novosibirsk is somewhat
higher than our findings in the present study.
In agreement with a recent population-based study in Rochester,
Minnesota,4 where no significant change in TIA incidence
for the last 3 decades (19601989) was reported, and with a recent
population-based study in Dijon, France,2 where the
incidence of TIA for 19851994 was stable, we found no significant
change in the incidence rate for first-ever TIA in Novosibirsk for the
last 10 years. However, there was a tendency toward increasing TIA
rate: the overall incidence of TIA, age- and sex-adjusted to the
European population, in Novosibirsk in 19961997 (27/100 000 [95%
CI, 9 to 79]) was 38% higher than that in 19871988 (17/100 000
[95% CI, 8 to 34]). The absence of any statistically significant
changes in the incidence of TIA in our population may partially be
explained by a relatively small number of TIA cases per study period,
resulting in the low statistical power of our study. The increase in
TIA incidence, although statistically insignificant, in Novosibirsk in
19961997 compared with 19871988 was most prominent in the older age
group (Table
). This increase corresponded to that in stroke and
other chronic noninfectious disorders.13 21 This can be
attributed to well-known social and economic changes observed in Russia
for the last decade (such as differences in medical care, in the
proportion of patients at risk who received effective treatment and
prevention, and in the prevalence of risk factors), and, given the role
of carotid and vertebrobasilar atherosclerosis in the
pathogenesis of TIAs,4 5 it may reflect an increase in the
prevalence of atherosclerotic large-vessel arterial disease
in the population during the last decade. Although it is possible that
the population at risk in 1989 was somewhat different from that in
19961997, we believe that these differences were not great enough to
substantially distort the inferences (the migration rate in the
population studied was <1% per year, and there is indirect evidence
that Novosibirsk had almost as many inhabitants in 19961997 as in
19871988).
The TIA incidence rate in 19871988, age- and sex-adjusted to the European population, was 9% of the annual stroke incidence rate in 19871988, and this proportion did not change significantly in 19961997, averaging approximately 10% for the entire study period. These ratios are similar to those reported in Sweden (16%),3 Estonia, USSR (18%),6 and Japan (5.5%)11 but are approximately 4 times lower than that reported in Rochester, Minnesota (41%).4 During 19851994, the ratio of TIA to ischemic stroke incidence in Dijon, France2 ranged from 14% to 35% in men and from 15% to 39% in women. While some methodological differences may account for the differences in the ratio of TIA to stroke in the populations compared, we agree with Brown et al4 that a true between-countries difference in the ratio of TIA to stroke is possible. A similar correlation of very low TIA incidence with relatively high stroke incidence was noted in Hisayama, Japan, in 1961198220 and in Kamogawa, Japan,11 in 19961997. However, the reason for relatively low incidence of TIA compared with the high stroke incidence in Novosibirsk remains to be studied. The low percentage of hospitalized patients with TIA (5%) in Novosibirsk is indicative of both the low awareness of the population with regard to symptoms of acute cerebrovascular events and the rather passive attitude of general practitioners toward treatment and management of patients with TIA.
Our data on the distribution of TIAs (80% of all TIAs occurred in the carotid distribution) are very similar to those reported in other population-based studies in Western Europe1 5 7 and the United States.4 Similar to these studies,1 4 the percentage of carotid TIAs in Novosibirsk is substantially higher than that reported in Japan.20 Our data confirm previous observations4 22 23 that TIA incidence, like incidence rates of acute myocardial infarction, exhibits no substantial geographic differences. A similarity of certain epidemiological characteristics of TIA and stroke observed in Novosibirsk further justifies the suggestion24 25 that TIA is a mild form of ischemic stroke. However, the absence of large geographic differences in the TIA incidence rates between various countries together with no significant change in the incidence of TIA over the last decades suggests that genetic and environmental factors play a lesser role in the occurrence of TIA than they do in the occurrence of ischemic stroke. This hypothesis should be tested in further studies.
The results of our population-based study indicate that unlike stroke incidence in Novosibirsk, Russia, TIA incidence rates in the population studied are similar to those in most other populations. As in other populations, the incidence of TIA increases with advancing age and constitutes approximately 10% of the annual stroke incidence rate. For the last decade in Novosibirsk, TIA incidence rates have shown a tendency to increase, especially in the older age group of the population, although this was statistically insignificant; this has correlated well with the increase in stroke incidence. Our data have implications for the planning of medical care and designing of clinical trials for TIA and stroke patients and for determining the cause of trends in acute cerebrovascular events.
| Acknowledgments |
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| Footnotes |
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Received June 19, 1999; revision received October 11, 1999; accepted October 26, 1999.
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