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Prevalence of symptomatic leg ischaemia in a swedish community—an epidemiological study
Eur J VascSurg 7, 432-437 (1993)
Prevalence of Symptomatic Leg Ischaemia in a Swedish CommunitynAn Epidemiological Study Tommy Skau and Bj6rn J6nsson Department of Vascular Surgery, University Hospital, Link6ping, Sweden The prevalence of symptomatic leg ischaemia (SLI) was studied using a standardised postal questionnaire and by measuring ankle systolic blood pressure among those with leg pain. All individuals, aged 50-89 years, of both sexes (n = 2748) in a community of 7524 inhabitants were included. The overall questionnaire response rate was 92 %, of whom 441 (17%) reported any form of leg pain. Ankle systolic blood pressure (ASBP) was measured in 353 (80%) of those. Ankle/brachial index (ABI) ~ 0.8 was chosen as the criterion for verified SLI. One hundred and seven (30%) had a verified SLI (ABI ~ 0.8). Hospital records could be reviewed in 83 % of the non-responders, and revealed corresponding distributions of risk factors among the non-responders and the questionnaire-responders. Risk factor frequencies among ASBP-examined and not examined individuals were also comparable. The overall prevalence of SU in the age 50-89 years was 4.1%, ranging from 1.5% in the age decade of 50-59 years, to maximum 7.1% in the decade 70-79 years. A slight but not significant male predominance was recorded, except for the age decade 70-79 years. The prevalence of SLI in the whole community population was approximately 2000/100 000 of which 5 % were possible candidatesfor vascular intervention. Key Words: Arterial occlusive disease; Intermittent claudication; Prevalence; Epidemiology.
Introduction Occlusion of peripheral arteries is a frequent manifestation of atherosclerosis and is closely related to age.2" 2 Not all occlusions are symptomatic3 and only a fraction of them are progressive with a potential risk for amputation. 4-6 Nevertheless, the number of amputations due to leg ischaemia has increased during the last decades. An incidence of up to 40 amputations/100000 has been reported in Sweden. 7 The social and economical consequences of an amputation are considerable, both for the patient and for society. With an increasing amount of elderly one can expect increasing problems with symptomatic leg ischaemia (SLI), and increasing demands for therapeutic intervention. Vascular and surgical techniques have improved in the last few decades, and seem, in many cases, to be able to prevent amputation. Epidemiological data of SLI are important, not the least for the planning of future health care resources. Prevalence studies are often restricted to a selected population. 1-3,s-13 This is probably a conse-
quence of the difficulty in obtaining valid data. The predominant method in such studies has been a standardised questionnaire either by postal or interview technique.14' 15 This has the advantage of a practical workload at low cost, and it carries a high specificity. 3"~6'17 A disadvantage though, is the low sensitivity of the questionnaire in field surveys. 16"17 The validity of the symptomatic diagnoses has to be secured by an accurate reference test. The aim of this study was to elucidate the prevalence of symptomatic leg ischaemia and its risk factors in an elderly community. A standardised questionnaire was the first step used to select individuals with any symptoms in the lower extremities. In a second phase ankle systolic blood pressure was measured among those with symptoms, to identify leg ischaemia.
Material and Methods The study population
Please address all correspondenceto: TommySkau, Departmentof Vascular Surgery, University Hospital, S-581 85 Link6ping, The study population was aged 50-89 years, of each Sweden. sex, living in the Vadstena community, Sweden. At 0950-821X/93/070432+06 $08.00/0© 1993Grune & StrattonLtd.
Prevalence of Leg Ischaemia
the time of the study, Vadstena had 7524 inhabitants of which 2784 (37%) were aged 50-89 years. Sex and age distributions in the study group were comparable to the general Swedish population (Swedish Statistical
Yearbook 1990).
The questionnaire In the first step of the study, a modified, self-administered version of the Rose questionnaire 15 was used to select individuals with any symptoms from the legs. Since we aimed at recording all leg symptoms and not only claudication, one modification was made by excluding the question "Does the pain ever begin w h e n you are standing still or sitting?" (question (b) in part C), which according to the Rose definition of claudication has to be answered in the negative. Instead, questions on leg ulcers unwilling to heal and rest-pain were added. The questionnaire also included questions on history/symptoms of coronary heart disease (CHD), cerebrovascular disease (CVD), diabetes, hypertension and smoking habits. Individuals reporting positive answers on all the questions on claudication in the modified questionnaire were considered to "probably" have SLI. Those reporting some but not all symptoms in the questionnaire were considered to "possibly" have ischaemia.
433
tations and vascular surgical procedures at the hospital serving the population of Vadstena were compared with the study population. Hospital data-files with this information were available for the 7 years prior to the investigation. When calculating the prevalence of SLI, the individuals outside the SLI-group, previously subjected to vascular surgery procedures or major amputation due to ischaemia, were included. The non-responder and the non-measured groups were considered to not include individuals with SLI, except those that had been subjected to amputation or vascular surgical procedures.
Results
Questionnaire and hospital record reviewing The overall response rate to the postal questionnaire was 92% (Fig. 1). Among the responders, 46% were
I Study population I Age 50-89 2784 Both sexes
I Resp°nders I 2557
I Non-responders 1227
]
Ankle systolic blood pressure measurement In the second phase of the study, all individuals with any questionnaire-recorded leg symptoms were called for brachial and ankle systolic blood pressure measurements. The ankle systolic blood pressure (ASBP) was recorded over the dorsalis pedis and posterior tibial arteries, with a Doppler ultrasonic flowmeter. The highest ASBP from the leg with the lowest pressure was recorded. The ankle/brachial index (ABI) was calculated by dividing the ankle systolic pressure by the brachial pressure. An ABI ~ 0.8 was chosen as criterion for verified SLI. All measurements were made by one specially trained nurse, in order to eliminate inter-observer deviations.
Prevalence calculation Hospital records of those individuals who did not respond to the questionnaire were reviewed to detect information about SLI and risk factors. All ampu-
Leg symptoms] 441
I No leg symptoms (= normals) I 2116
ASBP [ Examined 353
l Not examined J88
I Questionnaire: Probably isehaemia I 78(100%)
I Possibly QuestiOnnaire: ischaemia I 275(100%) 246 08 I
33(42%)
I ABI >
213(77%)
45(58%)
107 I ABI "<0.8 I
62(23%)
Fig. 1. Flow chart of the study. The definitions of "probable ischaemia" and "possible ischaemia" are given in the text. The ankle systolicblood pressure (ASBP)was measured in those with symptoms from the lower extremity, and ankle/brachial blood pressure index (ABI)was calculated. ABI ~<0.8 was considered to confirm leg ischaemia. Eur J Vasc SurgVol 7, July1993
T. Skau and B. JSnsson
434
60
50
50
40
I
4O
30 30
20
2O
]I ///A
10
0
10
~
Diabetes CVD MI HT >70 years Males Fig. 2. The frequencies of risk factors, e.g. history of diabetes, cerebrovascular disease (CVD), myocardial infarction (MI) and hypertension (HT), and the ratio of elderly and males among those w h o responded to the questionnaire ( ~ = responders; n = 2557) and among those who did not ( I = non-responders; n = 227). The non-responders' data could be analysed from hospital records in 83%.
men. No leg pain was reported by 2080 individuals (83%). Of 441 individuals complaining of leg pain, 91 (21%) were stratified to the group that, based on the questionnaire data, "probably" had symptoms of SLI. The 263 non-responders (8%) included 115 men (43%). Eighty-three per cent of the non-responders had hospital records that could be reviewed. Except for hypertension, which was significantly less frequent among non-responders (p < 0.05, ×2 analysis), the frequencies of all the recorded risk factors were comparable to the responder group (Fig. 2).
0 Diabetes CVD MI HT >70 years Males Fig. 3. The frequencies of risk factors, e.g. history of diabetes, cerebro vascular disease (CVD), myocardial infarction (MI) and hypertension (HT), and the ratio of elderly and males among those examined with ankle systolic blood pressure measuring ([] = examined; n = 353) and those who did not turn up for examination ( I = not examined; n = 88).
The group with ABI-verified SLI
Among the 107 with verified SLI (ABI ~< 0.8) 53% were men. In this group, 53 estimated a pain free walking distance as less than 100 m. Ankle pressure less than 50 m m H g was found in five individuals. The SLI-risk factors recorded were all, except for smoking habits and sex, significantly more frequent in the SLI group than in the symptom-free group (Fig. 4). In the whole study population, 18 individuals had been subjected to either lower extremity vascular surgery procedures or major amputations due to ischaemia (vascular surgery in 14, amputation in seven, and both in three cases). Ten of these 18 individuals were found in the SLI group.
Ankle pressure measurement
Ankle pressure was measured in 353 (80%) of the 441 individuals complaining of leg pain. Among the 88 w h o did not turn up for this examination, 17 had died. The frequencies of SLI risk factors registered in the questionnaire were comparable between the group that was examined and that which was not (Fig. 3). ABI /> 1.0 was found in 133 cases, 113 had ABI > 0.8 < 1.0, and 107 had an ABI ~< 0.8 (defined as SLI). Among those questionnaire-classified as "probably" SLI, 58% had ABI ~< 0.8 (Fig. 1). Eur J Vasc Surg Vol 7, July 1993
Prevalence
The calculated prevalence of SLI in the study population was 4.1%, ranging from 1.5% at 50-59 years to a maximum of 7.1% in the eighth decade. A slight but not significant predominance was recorded for men compared to w o m e n (4.5 vs. 3.8%) (Table 1). If the prevalence is calculated with the assumption that the SLI frequencies were comparable between the non-
Prevalence of Leg Ischaemia
435
responders and the responders, and between the non-measured and the measured groups, the result would be 5.3%. In the study population the recorded prevalence of CHD was four times and diabetes twice the prevalence of SLI, whereas CVD was slightly less frequent (Table 2).
60
50
40
Discussion 20
01 ]| Diabetes CVD
MI
HT
>70 Males Smokers years Fig. 4. The frequencies of risk factors, e.g. history of diabetes, cerebro vascular disease (CVD), myocardial infarction (MI) and hypertension (HT) and the ratio of elderly, males and smokers among those with verified symptomatic leg ischaemia (IN = SLIgroup; n = 107) and those who reported no symptoms in the questionnaire ( I = normals; n = 2116).
Table 1. The prevalence of symptomatic leg ischaemia in the study population, considering age and sex Prevalence (%) Age (years)
Both sexes
Males
Females
50-59
1.5
1.8
1.2
60-69
3.6
5.0
2.3
70-79
7.1
6.3
7.7
80-89
5.3
6.9
4.7
All ages
4.1
4.5
3.8
Table 2. Prevalences of the questionnaire-recorded diseases in the study population Disease
Prevalence (%)
Hypertension
24.4
Diabetes mellitus Coronary heart disease
9.4 15.7
Symptomatic leg ischaemia
4.1
Cerebrovascular disease
3.3
The prevalence of a disease in a population study is dependent on the diagnostic criteria and study method used, including the selection of individuals. Results of prevalence reported from different studies can therefore vary due to different study designs. In contrast to this study, most epidemiological studies on peripheral arterial disease have been restricted to a male population. Our results seem consistent with many previous European studies of SLI prevalence (Table 3). Standardised questionnaries, either by postal or interview technique, enables the study of large populations at a low cost with an acceptable workload. There are, however, diverging reports concerning the validity of the claudication questionnaire. 1°'11' 15,18 False positives, mainly due to musculoskeletal disorders, venous disturbance or misunderstanding of the questionnaire, 1 and false negatives, possibly due to other physical conditions which restrict physical activity, 13 have been demonstrated. It is obvious, that prevalence figures in population surveys cannot be based solely on the questionnaire, but some reference method has to be utilised. In this study, the questiom naire was used to detect any kind of leg symptoms, in order to select a study group for a more accurate analysis of ischaemia with a non-invasive diagnostic procedure. As we aimed at detecting symptomatic ischaemia, lots of false positives were selected, but probably only a minimum of false negatives were lost in this questionnaire phase. The ASBP examination is less expensive and time-consuming than many other non-invasive examination methods that have been used in population surveys. 17'19'20 However, any non-invasive test is resource consuming when screening large populations but the questionnaire selection as used here reduced the ASBP procedure to approximately onefifth of the study population. Hylthema demonstrated in 1976 that an ABI < 0.9 detects almost all occlusions in the iliac, femoral and popliteal arteries. 21 Its reproducibility in studies on hospital patients and the good correlation beEur J Vasc Surg Vol 7, July 1993
436
T. Skau and B. JOnsson
Table 3. Resume of European population studies presented during the last two decades: Prevalence (%) of symptoms of lower extremity ischaemic disease
Prevalence (%) within age-group Study
Year
Sex
30-39
40-49
50-59
Helsinki1
1982
M
1.1
1.6
2.8
Copenhagen8
1973
M
1.4
3.1
London9
1974
M
0.6
0.8
Paris10
1972
M
0.8
1.1
Belgium11
1979
M
0.8
2.3
Berlin12
1976
M
3.4
MOSCOW12
1976
M
6.9
Malta6~3
1972
M
2.8
This study
1992
M+ F
1.5
tween ASBP measured indirectly by the Dopplertechnique and also directly, has been proven by others 16'22-24. In a study by Carter, 2s the ABI was found to be <0.82 in cases of at least one occlusion. The accuracy of the method in general populations though is not entirely elucidated. ~9 In studies on young or middle-aged subjects, where the prevalence of SLI is low, its accuracy as a diagnostic standard tends to decrease due to misclassification. 26 To minimise this potential problem, we chose a low ABIlimit (~<0.8) as the criterion for verified SLI. The improved specificity, however, was probably at the cost of a reduced sensitivity. As the ABI-stratification is the basis for the prevalence figures in this study, it is reasonable therefore to assume that prevalence is underestimated rather than overestimated. In addition to this, possible undetected SLI-individuals in the non-responder and the non-measured groups were not included in the calculation of prevalence. The non-responders in a postal questionnaire survey represent a special problem, and in many studies they have simply been left out when prevalance has been calculated. Though one might assume that this group is not equally composed compared to the responders, we were able to analyse medical records in a vast majority (83%) of these subjects. Age, sex, diabetes, coronary heart disease and hypertension all correlate to SLI. 18•26- 28 The frequency of all these factors except hypertension were comparable between the non-responders and the studied group, indicating a minor possibility of non-valid prevalence results due to the drop-outs. If one assumes that the non-responder group and the non-examined group Eur J VascSurg Vol 7, July1993
60-69
70-79
80-89
3.6
7.1
5.3
included comparable frequencies of leg ischaemia, the calculated prevalence of SLI in the study would increase to 5.3%. We conclude that the true prevalence in this study is somewhere between 4.1 and 5.3%. The low individual correlation found between "questionnaire-SLI" and "ABI-verified-SLI" probably reflects a combination of the low specificity of the questionnaire to detect claudication in a population survey, and the low sensitivity of the ABI-criterion. Among those aged 40-49 years, not included in our study, previous studies have demonstrated a prevalence of between 0.6-1.6%. 1'8-11 Presuming an SLI prevalence of approximately 1% in this age group, and not taking the extremely rare SLI cases in ages below 40 years into account, our figures give a prevalence of SLI in the total community population of approximately 2000/100 000. These results indicate that SLI is common in adult populations, although regional variations can exist. 1,12 This study confirms the observation that w o m e n develop atherosclerosis, including SLI, some years after men. 1 The declining prevalence among both males and females in the ninth age decade probably reflects the higher mortality observed in SLI patients. 29 Both the prevalence and severity of the disease increase with age. The age and sex distribution therefore are important parameters to consider when evaluating prevalence figures and calculating therapeutic demands. Knowledge of SLI prevalence is not sufficient w h e n calculating the need for therapeutic interventions. The indication for vascular surgical interven-
T. Skau and B. J6nsson
tion in SLI is multifactorial, including not only the age of the patient and severity of symptoms, but also the individual physical activity capacity regardless of the SLI, concomittant diseases, the level of the vascular occlusions etc. Therefore this study does not allow proper evaluation of the potential therapeutic demands of SLI in the population. However, one can suspect that at least those with signs of severe ischaemia, e.g. ABP < 50mmHg, are potential candidates for vascular surgery. This group consisted of approximately 5% of the SLI-subjects, or approximately 100/ 100 000 in a community population. Despite the vascular surgical expansion of the last few decades, many Swedish vascular surgical centres perform less than 100 arterial interventions for leg ischaemia per 100000 inhabitants and year. 3° Our results indicate that the number of vascular interventions for SLI may still be suboptimal in Sweden.
References 1 REUNANENA, TAKKUNENH, AROMAAA. Prevalence of intermittent claudication and its effect on mortality. Acta Med Scand 1982; 211: 249-256. 2 CRIQUI MH, FRONEK A, BARRETT-CONNORE, KLAUBER MR, GABRIEL S, GOODMAN D. The prevalence of peripheral arterial disease in a defined population. Circulation 1985; 71: 510-515. 3 WIDMERLK, GREENSHERA,KANNELWB.Occlusionofperipheral arteries: a study on 6400 working subjects. Circulation 1964; 30: 836-842. 4 IMPARATOAIVI, GEuN-EUN K, DAVIDSON T, CROWLEYJG. Intermittent clavdication: its natural course. Surgery 1975; 78: 795799. 5 WILSONSE, SCHWARTZI, WILLIAMSRA, OWENSML. Occlusion of the superficial femoral artery: what happens without operation. Am J Surg 1980; 140: 112-118. 6 JELNESR, GAARDSTINGO, HOUGAARDJENSENK, BAEKGAARDN, TOENNESEN KH, SCHROEDERT. Fate in intermittent daudication: outcome and risk factors. BM] 1986; 293: 1137-1140. 7 KALD A, CARLSSONR, NILSON E. Major amputation in a defined population: incidence, mortality and results of treatment. Br J Surg 1989; 76: 308-310. 8 GYNTELBERG F. Physical fitness and coronary heart disease. Male residents in Copenhagen aged 40-59. Dan Med Bull 1973; 20: 1-4. 9 REID DD, BRETTGZ, HAMILTON PJS, JARRETTRJ, KEEN H, ROSEG. Cardiorespiratory disease and diabetes among middle-aged male civil servants. A study on screening intervention. Lancet 1974; 1: 469-473. 10 RICHARDJL, DUCIMETIEREP, ELGRISHII, GELIN J. D6pistage par questionnaire de l'insufficance coronarienne et de la claudication intermittente. Rev EpidemioI Med Soc Sante Publique 1972; 20: 735-741. 11 DEBACKERG, KORNITZERM, SOBOLSKIJ, DENOLIN H. Intermittent claudication--epidemiology and natural history. Acta Cardiol 1979; 34: 115-124.
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12 BOTHIGS, METELITSAV, BARTHW, et al. Prevalence of ischaemic heart disease, arterial hypertension and intermittent claudication and distribution of risk factors a m o n g middleaged men in Moscow and Berlin. Cur Vasa 1976; 18: 104-118. 13 ISACSSON S-O. Venous occlusion plethysmography in 55-yearold men. A population study in Malm6, Sweden. Acta Med Scand 1972; 537 (Suppl): 1-62. 14 ROSE GA. The diagnosis of ischaemic heart pain and intermittent claudication in field surveys. Bull W H O 1962; 27: 645-658. 15 ROSE G, McCARTNEY P, REID DD. Self-administration of a questinnaire on chest pain and intermittent claudication. Br J Prev Soc Med 1977; 31: 42-48. 16 SCrlROLLM, MUNCH O. Estimation of peripheral arteriosclerotic disease by ankle pressure measurements in a population study of 60-year-old men and women. J Chron Dis 1981; 34: 261-269. 17 CRIQUI MH, FRONEK A, KLAUBER MR, BARRETT-CONNOR E, GABRIEL S. The sensitivity, specificity, a n d predictive value of traditional clinical evaluation of peripheral arterial disease: results from noninvasive testing in a defined population. Circulation 1985; 71: 516-522. 18 DAGENAISG, MAURICES, ROBITAILLENM, GINGRASS, LUPIENPJ. Intermittent claudication in Quebec men from 1974-1986: the Quebec cardiovascular study. Clin Invest Med 1991; 14:2: 93-100. 19 FOWKES FGR. The measurement of atherosclerotic peripheral arterial disease in epidemiological surveys. Int J Epidem 1988; 17: 248-254. 20 OURIELK, McDONNELL AE, METZCE, ZARINS CK. Critical evaluation of stress testing in the diagnosis of peripheral vascular disease. Surgery 1982; 91: 686-693. 21 HYLTHEMA BS. Diagnostick van arteriele circulastiestoornissen in der b e n e n door bloeddrukmetingen met behalp van ultrageluid. Ned T Geneesk 1976; 120: 733-742. 22 BOLLINGER A, MAHLER E, ZEHENDER O. Kombinierte D r u c k - u n d Durchflussmessungen in der Beurteilung arterieller Durchblutungst6ringen. Dtsch Med Wschr 1970; 95: 1039-1043. 23 BOLLINGERA, BARRASJP, MAHLERF. Measurement of foot artery blood pressure by micromanometry in normal subjects and in patients with arterial occlusive disease. Circulation 1976; 53: 506-512. 24 JOHNSTON KW, HOSANG MY, ANDREWS DF. Reproducibility of noninvasive vascular laboratory measurements of the peripheral circulation, l Vasc Surg 1987; 6: 147-151. 25 CARTER SA. Indirect systolic pressures a n d pulse waves in arterial occlusive disease of the lower extremities. Circulation 1968; 37: 624-637. 26 GOFIN R, KARKJD, FRIEDLANDERY, LEWIS BS, WITT H, STEIN Y, GOTSMAN MS. Peripheral vascular disease in a middle-aged population sample. The Jerusalem lipid research clinic prevalence study. Isr J Med Sci 1987; 23: 157-167. 27 VYDEN JK, THORNER J, NAGASAWA K, TAKANO T, GROSETHDITTRICH MF, PERLOWR, SWANHJC. Metabolic and cardiovascular abnormalities in patients with peripheral arterial disease. Am Heart J 1975; 90: 703-708. 28 BRAND FN, ABBOTT RD, KANNEL WB. Diabetes, intermittent claudication, and risk of cardiovascular events. The Framingham study. Diabetes 1989; 38: 504-509. 29 DORMANDY J, MAI-IIR M, ASCADY G, BALSANO F, DE LEEUW P, BLOMBERYP, et al. Fate of the patient with chronic leg ischaemia. J Cardiovasc Surg 1989; 30: 50-57. 30 BERGQVISTD. Enk~it om svensk k~irlkirurgi 1983: Antalet operationer hat 6kat markant men ~innu /Jr behovet troligen inte t/ickt. Ltikartidningen 1985; 82: 3490-3491.
Accepted 5 February 1993
Eur J Vasc Surg Vol 7, July 1993
Prevalence of Symptomatic Leg Ischaemia in a Swedish CommunitynAn Epidemiological Study Tommy Skau and Bj6rn J6nsson Department of Vascular Surgery, University Hospital, Link6ping, Sweden The prevalence of symptomatic leg ischaemia (SLI) was studied using a standardised postal questionnaire and by measuring ankle systolic blood pressure among those with leg pain. All individuals, aged 50-89 years, of both sexes (n = 2748) in a community of 7524 inhabitants were included. The overall questionnaire response rate was 92 %, of whom 441 (17%) reported any form of leg pain. Ankle systolic blood pressure (ASBP) was measured in 353 (80%) of those. Ankle/brachial index (ABI) ~ 0.8 was chosen as the criterion for verified SLI. One hundred and seven (30%) had a verified SLI (ABI ~ 0.8). Hospital records could be reviewed in 83 % of the non-responders, and revealed corresponding distributions of risk factors among the non-responders and the questionnaire-responders. Risk factor frequencies among ASBP-examined and not examined individuals were also comparable. The overall prevalence of SU in the age 50-89 years was 4.1%, ranging from 1.5% in the age decade of 50-59 years, to maximum 7.1% in the decade 70-79 years. A slight but not significant male predominance was recorded, except for the age decade 70-79 years. The prevalence of SLI in the whole community population was approximately 2000/100 000 of which 5 % were possible candidatesfor vascular intervention. Key Words: Arterial occlusive disease; Intermittent claudication; Prevalence; Epidemiology.
Introduction Occlusion of peripheral arteries is a frequent manifestation of atherosclerosis and is closely related to age.2" 2 Not all occlusions are symptomatic3 and only a fraction of them are progressive with a potential risk for amputation. 4-6 Nevertheless, the number of amputations due to leg ischaemia has increased during the last decades. An incidence of up to 40 amputations/100000 has been reported in Sweden. 7 The social and economical consequences of an amputation are considerable, both for the patient and for society. With an increasing amount of elderly one can expect increasing problems with symptomatic leg ischaemia (SLI), and increasing demands for therapeutic intervention. Vascular and surgical techniques have improved in the last few decades, and seem, in many cases, to be able to prevent amputation. Epidemiological data of SLI are important, not the least for the planning of future health care resources. Prevalence studies are often restricted to a selected population. 1-3,s-13 This is probably a conse-
quence of the difficulty in obtaining valid data. The predominant method in such studies has been a standardised questionnaire either by postal or interview technique.14' 15 This has the advantage of a practical workload at low cost, and it carries a high specificity. 3"~6'17 A disadvantage though, is the low sensitivity of the questionnaire in field surveys. 16"17 The validity of the symptomatic diagnoses has to be secured by an accurate reference test. The aim of this study was to elucidate the prevalence of symptomatic leg ischaemia and its risk factors in an elderly community. A standardised questionnaire was the first step used to select individuals with any symptoms in the lower extremities. In a second phase ankle systolic blood pressure was measured among those with symptoms, to identify leg ischaemia.
Material and Methods The study population
Please address all correspondenceto: TommySkau, Departmentof Vascular Surgery, University Hospital, S-581 85 Link6ping, The study population was aged 50-89 years, of each Sweden. sex, living in the Vadstena community, Sweden. At 0950-821X/93/070432+06 $08.00/0© 1993Grune & StrattonLtd.
Prevalence of Leg Ischaemia
the time of the study, Vadstena had 7524 inhabitants of which 2784 (37%) were aged 50-89 years. Sex and age distributions in the study group were comparable to the general Swedish population (Swedish Statistical
Yearbook 1990).
The questionnaire In the first step of the study, a modified, self-administered version of the Rose questionnaire 15 was used to select individuals with any symptoms from the legs. Since we aimed at recording all leg symptoms and not only claudication, one modification was made by excluding the question "Does the pain ever begin w h e n you are standing still or sitting?" (question (b) in part C), which according to the Rose definition of claudication has to be answered in the negative. Instead, questions on leg ulcers unwilling to heal and rest-pain were added. The questionnaire also included questions on history/symptoms of coronary heart disease (CHD), cerebrovascular disease (CVD), diabetes, hypertension and smoking habits. Individuals reporting positive answers on all the questions on claudication in the modified questionnaire were considered to "probably" have SLI. Those reporting some but not all symptoms in the questionnaire were considered to "possibly" have ischaemia.
433
tations and vascular surgical procedures at the hospital serving the population of Vadstena were compared with the study population. Hospital data-files with this information were available for the 7 years prior to the investigation. When calculating the prevalence of SLI, the individuals outside the SLI-group, previously subjected to vascular surgery procedures or major amputation due to ischaemia, were included. The non-responder and the non-measured groups were considered to not include individuals with SLI, except those that had been subjected to amputation or vascular surgical procedures.
Results
Questionnaire and hospital record reviewing The overall response rate to the postal questionnaire was 92% (Fig. 1). Among the responders, 46% were
I Study population I Age 50-89 2784 Both sexes
I Resp°nders I 2557
I Non-responders 1227
]
Ankle systolic blood pressure measurement In the second phase of the study, all individuals with any questionnaire-recorded leg symptoms were called for brachial and ankle systolic blood pressure measurements. The ankle systolic blood pressure (ASBP) was recorded over the dorsalis pedis and posterior tibial arteries, with a Doppler ultrasonic flowmeter. The highest ASBP from the leg with the lowest pressure was recorded. The ankle/brachial index (ABI) was calculated by dividing the ankle systolic pressure by the brachial pressure. An ABI ~ 0.8 was chosen as criterion for verified SLI. All measurements were made by one specially trained nurse, in order to eliminate inter-observer deviations.
Prevalence calculation Hospital records of those individuals who did not respond to the questionnaire were reviewed to detect information about SLI and risk factors. All ampu-
Leg symptoms] 441
I No leg symptoms (= normals) I 2116
ASBP [ Examined 353
l Not examined J88
I Questionnaire: Probably isehaemia I 78(100%)
I Possibly QuestiOnnaire: ischaemia I 275(100%) 246 08 I
33(42%)
I ABI >
213(77%)
45(58%)
107 I ABI "<0.8 I
62(23%)
Fig. 1. Flow chart of the study. The definitions of "probable ischaemia" and "possible ischaemia" are given in the text. The ankle systolicblood pressure (ASBP)was measured in those with symptoms from the lower extremity, and ankle/brachial blood pressure index (ABI)was calculated. ABI ~<0.8 was considered to confirm leg ischaemia. Eur J Vasc SurgVol 7, July1993
T. Skau and B. JSnsson
434
60
50
50
40
I
4O
30 30
20
2O
]I ///A
10
0
10
~
Diabetes CVD MI HT >70 years Males Fig. 2. The frequencies of risk factors, e.g. history of diabetes, cerebrovascular disease (CVD), myocardial infarction (MI) and hypertension (HT), and the ratio of elderly and males among those w h o responded to the questionnaire ( ~ = responders; n = 2557) and among those who did not ( I = non-responders; n = 227). The non-responders' data could be analysed from hospital records in 83%.
men. No leg pain was reported by 2080 individuals (83%). Of 441 individuals complaining of leg pain, 91 (21%) were stratified to the group that, based on the questionnaire data, "probably" had symptoms of SLI. The 263 non-responders (8%) included 115 men (43%). Eighty-three per cent of the non-responders had hospital records that could be reviewed. Except for hypertension, which was significantly less frequent among non-responders (p < 0.05, ×2 analysis), the frequencies of all the recorded risk factors were comparable to the responder group (Fig. 2).
0 Diabetes CVD MI HT >70 years Males Fig. 3. The frequencies of risk factors, e.g. history of diabetes, cerebro vascular disease (CVD), myocardial infarction (MI) and hypertension (HT), and the ratio of elderly and males among those examined with ankle systolic blood pressure measuring ([] = examined; n = 353) and those who did not turn up for examination ( I = not examined; n = 88).
The group with ABI-verified SLI
Among the 107 with verified SLI (ABI ~< 0.8) 53% were men. In this group, 53 estimated a pain free walking distance as less than 100 m. Ankle pressure less than 50 m m H g was found in five individuals. The SLI-risk factors recorded were all, except for smoking habits and sex, significantly more frequent in the SLI group than in the symptom-free group (Fig. 4). In the whole study population, 18 individuals had been subjected to either lower extremity vascular surgery procedures or major amputations due to ischaemia (vascular surgery in 14, amputation in seven, and both in three cases). Ten of these 18 individuals were found in the SLI group.
Ankle pressure measurement
Ankle pressure was measured in 353 (80%) of the 441 individuals complaining of leg pain. Among the 88 w h o did not turn up for this examination, 17 had died. The frequencies of SLI risk factors registered in the questionnaire were comparable between the group that was examined and that which was not (Fig. 3). ABI /> 1.0 was found in 133 cases, 113 had ABI > 0.8 < 1.0, and 107 had an ABI ~< 0.8 (defined as SLI). Among those questionnaire-classified as "probably" SLI, 58% had ABI ~< 0.8 (Fig. 1). Eur J Vasc Surg Vol 7, July 1993
Prevalence
The calculated prevalence of SLI in the study population was 4.1%, ranging from 1.5% at 50-59 years to a maximum of 7.1% in the eighth decade. A slight but not significant predominance was recorded for men compared to w o m e n (4.5 vs. 3.8%) (Table 1). If the prevalence is calculated with the assumption that the SLI frequencies were comparable between the non-
Prevalence of Leg Ischaemia
435
responders and the responders, and between the non-measured and the measured groups, the result would be 5.3%. In the study population the recorded prevalence of CHD was four times and diabetes twice the prevalence of SLI, whereas CVD was slightly less frequent (Table 2).
60
50
40
Discussion 20
01 ]| Diabetes CVD
MI
HT
>70 Males Smokers years Fig. 4. The frequencies of risk factors, e.g. history of diabetes, cerebro vascular disease (CVD), myocardial infarction (MI) and hypertension (HT) and the ratio of elderly, males and smokers among those with verified symptomatic leg ischaemia (IN = SLIgroup; n = 107) and those who reported no symptoms in the questionnaire ( I = normals; n = 2116).
Table 1. The prevalence of symptomatic leg ischaemia in the study population, considering age and sex Prevalence (%) Age (years)
Both sexes
Males
Females
50-59
1.5
1.8
1.2
60-69
3.6
5.0
2.3
70-79
7.1
6.3
7.7
80-89
5.3
6.9
4.7
All ages
4.1
4.5
3.8
Table 2. Prevalences of the questionnaire-recorded diseases in the study population Disease
Prevalence (%)
Hypertension
24.4
Diabetes mellitus Coronary heart disease
9.4 15.7
Symptomatic leg ischaemia
4.1
Cerebrovascular disease
3.3
The prevalence of a disease in a population study is dependent on the diagnostic criteria and study method used, including the selection of individuals. Results of prevalence reported from different studies can therefore vary due to different study designs. In contrast to this study, most epidemiological studies on peripheral arterial disease have been restricted to a male population. Our results seem consistent with many previous European studies of SLI prevalence (Table 3). Standardised questionnaries, either by postal or interview technique, enables the study of large populations at a low cost with an acceptable workload. There are, however, diverging reports concerning the validity of the claudication questionnaire. 1°'11' 15,18 False positives, mainly due to musculoskeletal disorders, venous disturbance or misunderstanding of the questionnaire, 1 and false negatives, possibly due to other physical conditions which restrict physical activity, 13 have been demonstrated. It is obvious, that prevalence figures in population surveys cannot be based solely on the questionnaire, but some reference method has to be utilised. In this study, the questiom naire was used to detect any kind of leg symptoms, in order to select a study group for a more accurate analysis of ischaemia with a non-invasive diagnostic procedure. As we aimed at detecting symptomatic ischaemia, lots of false positives were selected, but probably only a minimum of false negatives were lost in this questionnaire phase. The ASBP examination is less expensive and time-consuming than many other non-invasive examination methods that have been used in population surveys. 17'19'20 However, any non-invasive test is resource consuming when screening large populations but the questionnaire selection as used here reduced the ASBP procedure to approximately onefifth of the study population. Hylthema demonstrated in 1976 that an ABI < 0.9 detects almost all occlusions in the iliac, femoral and popliteal arteries. 21 Its reproducibility in studies on hospital patients and the good correlation beEur J Vasc Surg Vol 7, July 1993
436
T. Skau and B. JOnsson
Table 3. Resume of European population studies presented during the last two decades: Prevalence (%) of symptoms of lower extremity ischaemic disease
Prevalence (%) within age-group Study
Year
Sex
30-39
40-49
50-59
Helsinki1
1982
M
1.1
1.6
2.8
Copenhagen8
1973
M
1.4
3.1
London9
1974
M
0.6
0.8
Paris10
1972
M
0.8
1.1
Belgium11
1979
M
0.8
2.3
Berlin12
1976
M
3.4
MOSCOW12
1976
M
6.9
Malta6~3
1972
M
2.8
This study
1992
M+ F
1.5
tween ASBP measured indirectly by the Dopplertechnique and also directly, has been proven by others 16'22-24. In a study by Carter, 2s the ABI was found to be <0.82 in cases of at least one occlusion. The accuracy of the method in general populations though is not entirely elucidated. ~9 In studies on young or middle-aged subjects, where the prevalence of SLI is low, its accuracy as a diagnostic standard tends to decrease due to misclassification. 26 To minimise this potential problem, we chose a low ABIlimit (~<0.8) as the criterion for verified SLI. The improved specificity, however, was probably at the cost of a reduced sensitivity. As the ABI-stratification is the basis for the prevalence figures in this study, it is reasonable therefore to assume that prevalence is underestimated rather than overestimated. In addition to this, possible undetected SLI-individuals in the non-responder and the non-measured groups were not included in the calculation of prevalence. The non-responders in a postal questionnaire survey represent a special problem, and in many studies they have simply been left out when prevalance has been calculated. Though one might assume that this group is not equally composed compared to the responders, we were able to analyse medical records in a vast majority (83%) of these subjects. Age, sex, diabetes, coronary heart disease and hypertension all correlate to SLI. 18•26- 28 The frequency of all these factors except hypertension were comparable between the non-responders and the studied group, indicating a minor possibility of non-valid prevalence results due to the drop-outs. If one assumes that the non-responder group and the non-examined group Eur J VascSurg Vol 7, July1993
60-69
70-79
80-89
3.6
7.1
5.3
included comparable frequencies of leg ischaemia, the calculated prevalence of SLI in the study would increase to 5.3%. We conclude that the true prevalence in this study is somewhere between 4.1 and 5.3%. The low individual correlation found between "questionnaire-SLI" and "ABI-verified-SLI" probably reflects a combination of the low specificity of the questionnaire to detect claudication in a population survey, and the low sensitivity of the ABI-criterion. Among those aged 40-49 years, not included in our study, previous studies have demonstrated a prevalence of between 0.6-1.6%. 1'8-11 Presuming an SLI prevalence of approximately 1% in this age group, and not taking the extremely rare SLI cases in ages below 40 years into account, our figures give a prevalence of SLI in the total community population of approximately 2000/100 000. These results indicate that SLI is common in adult populations, although regional variations can exist. 1,12 This study confirms the observation that w o m e n develop atherosclerosis, including SLI, some years after men. 1 The declining prevalence among both males and females in the ninth age decade probably reflects the higher mortality observed in SLI patients. 29 Both the prevalence and severity of the disease increase with age. The age and sex distribution therefore are important parameters to consider when evaluating prevalence figures and calculating therapeutic demands. Knowledge of SLI prevalence is not sufficient w h e n calculating the need for therapeutic interventions. The indication for vascular surgical interven-
T. Skau and B. J6nsson
tion in SLI is multifactorial, including not only the age of the patient and severity of symptoms, but also the individual physical activity capacity regardless of the SLI, concomittant diseases, the level of the vascular occlusions etc. Therefore this study does not allow proper evaluation of the potential therapeutic demands of SLI in the population. However, one can suspect that at least those with signs of severe ischaemia, e.g. ABP < 50mmHg, are potential candidates for vascular surgery. This group consisted of approximately 5% of the SLI-subjects, or approximately 100/ 100 000 in a community population. Despite the vascular surgical expansion of the last few decades, many Swedish vascular surgical centres perform less than 100 arterial interventions for leg ischaemia per 100000 inhabitants and year. 3° Our results indicate that the number of vascular interventions for SLI may still be suboptimal in Sweden.
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Accepted 5 February 1993
Eur J Vasc Surg Vol 7, July 1993