No difference in the incidences of vasculitides between north and south Germany: first results of the German vasculitis register
E. Reinhold-Keller,
K. Herlyn,
R. Wagner-Bastmeyer,
J. Gutfleisch1,
H. H. Peter1,
H. H. Raspe2 and
W. L. Gross
Department of Rheumatology of the Medical University of Lübeck and Rheumaklinik Bad Bramstedt GmbH,
1 Department of Rheumatology and Clinical Immunology of the Medical University of Freiburg and
2 Department of Social Medicine of the Medical University of Lübeck, Germany
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Abstract
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Objective. To register all newly diagnosed patients with primary systemic vasculitis (PSV) in two large regions in north and south Germany.
Methods. Between 1 January 1998 and 31 December 1999, all newly diagnosed cases of PSV, as defined by the Chapel Hill Consensus Conference 1992, were identified in two large mixed rural/urban regions in north and south Germany with a combined population of 4 880 543, for a population-based prospective study. The following sources were used: (i) all departments of every hospital, including their out-patient clinics; (ii) all departments of pathology; and (iii) all reference immunological laboratories serving the catchment area. All cases were re-evaluated by the authors.
Results. Over the whole period, 473 individuals were registered as having a new PSV. The incidence rates for all PSV were 54 cases per 1 000 000 inhabitants in the north and 48 in the south in 1998, and 48 and 41 respectively in 1999. People 50 yr and older had a three- to five-fold higher risk of getting PSVs than those under 50 yr. The incidences of antineutrophil cytoplasmic antibody (ANCA)-associated PSVs [Wegener's granulomatosis (WG), microscopic polyangiitis (MPA) and ChurgStrauss syndrome (CSS)] remained stable in both regions, at about 9.5 per 1 000 000 annually. The incidence of WG was two to three times greater than those of MPA and CSS. There was no difference in incidence rates between north and south Germany.
Conclusion. First results from a population-based vasculitis register serving nearly 5 000 000 inhabitants in north and south Germany revealed no regional differences in the incidence of all PSVs between north and south. The incidence rates of ANCA-associated PSVs, such as WG and MPA, were lower than those in the UK and Norway but higher than that in Spain.
KEY WORDS: Epidemiology, Primary systemic vasculitides, Wegener's granulomatosis, ANCA-associated vasculitides.
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Introduction
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Little has been published on the epidemiology of primary systemic vasculitides (PSV) since the introduction of new criteria for the classification and definition of PSV, including abortive courses of the diseases [1, 2]. Much of the available data comes from referral centres or covers only small areas [39], possibly leading to referral or selection bias. For most types of PSV an increase in incidence has been reported, an example being giant cell arteritis (GCA) [10]. An increase in the incidence of small vessel vasculitides has been observed since the introduction in the mid-1980s of highly specific autoantibodies [antineutrophil cytoplasmic antibodies (ANCA)] associated with Wegener's granulomatosis (WG), microscopic polyangiitis (MPA) and ChurgStrauss syndrome (CSS)] [9, 11, 12]. Recently published data on the epidemiology of ANCA-associated PSV and (classical) polyarteritis nodosa (PAN) over 11 yr (19881998) from the Norwich Health Authority in the UK showed a slow increase over time as well as an increase with age [7, 9], the opposite of what occurred in Spain over the same period [6, 9]. Although the overall yearly incidence of these four PSV entities was similar in the UK and Spain (18.9 and 18.3 per million inhabitants respectively), differences were found for WG. The incidence of WG in Spain was only half that in the UK and was also nearly half that in Norway [8]. In short, WG seems to be less frequent in southern than in northern Europe; similarly, GCA has a higher incidence in northern Europe than in the Mediterranean countries [10, 1319]. In addition, Cotch et al. [20] also observed marked differences in the geographical distribution of the prevalence of WG in New York State, ranging from no cases to 170 cases per million [20]. In a previous population-based epidemiological study, we investigated the period prevalence of all PSVs in areas of north and south Germany (approximately 700 km apart), comprising two cities and two rural regions with nearly 900 000 habitants [21]. That study revealed significantly higher prevalence rates of PSV in the cities compared with the rural regions. This prompted us to establish a vasculitis register for north and south Germany from 1 January 98. In two regions with a combined population of nearly 5 000 000 habitants, all newly diagnosed cases of PSV, as defined by the Chapel Hill Consensus Conference (CHC) 1992 on the Nomenclature of PSV [2], were registered in this population-based study. The primary objective was to determine for the first time the incidence of PSVs in a large region. Secondly, we were interested in comparing north with south Germany. We report here the incidences documented over the first 2 yr of operation of this population-based register.
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Methods
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Catchment area and study population
The catchment areas contained 2 766 057 inhabitants in the north (the entire Federal State of Schleswig-Holstein) and 2 114 486 in the south (the south-western part of the Federal State of Baden-Württemberg), giving a total of 4 880 543 inhabitants (Fig. 1
). Both regions included the departments where the authors are employed. For further details of the demographic structure, including the health-care systems and participating clinics, see Table 1
. All calculations were based on the population statistics for the end of 1998, obtained from the Departments of Vital Statistics of the Federal States of Schleswig-Holstein and Baden-Württemberg. The catchment areas in the north and south are separated by about 700 km. The population of the catchment area consists of nearly 100% of Caucasians. Neither area includes regions preferred by non-Caucasian immigrants. Both regions include urban and rural areas. More than half of the people (56%) live in cities with more than 10 000 inhabitants and 44% live in rural regions. In both areas the population was stable, with a migration/immigration rate of 67% during the period from 1995 to 1998 and 23% for the population 50 yr and older.
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TABLE 1. Characteristics of the regions of the German vasculitis register, representing a total population of 4 880 543 (statistics for 31 December 1998)
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Study period
The study period ran from 1 January 1998 to 31 December 1999.
Sources
Data on all newly diagnosed cases of PSV were obtained from the following sources: (i) all departments of all hospitals including their out-patient clinics, and including the departments at which the authors are employed; (ii) all departments of pathology; and (iii) all reference immunology laboratories serving the respective catchment areas (see also Table 1
). At intervals of 3 months, all sources were asked by mail (up to three times if there was no initial response) to screen for PSV cases diagnosed during the previous 3 months. If there was no response to all three mailings, the authors contacted the physicians by telephone. The data (for most patients, the medical records) obtained from all sources were re-evaluated by the authors.
All patients who were registered received a disease information pack containing written information on their disease, the location of places where patient vasculitis education courses were being offered, and the addresses of support groups.
Inclusion criteria
The following types of PSV, defined by the 1992 CHC [2], were registered: GCA (temporal arteritis), Takayasu arteritis, WG, MPA, CSS, HenochSchönlein purpura (HSP), (isolated) cutaneous leucocytoclastic vasculitis (CLA), (classical) polyarteritis nodosa (PAN) and Kawasaki syndrome. In addition, the American College of Rheumatology (ACR) criteria for the classification of vasculitides were applied, except for MPA and CLA, which are not included in the ACR criteria. The diagnosis of unclassified PSV was also included if a definite allocation was not possible. Patients diagnosed with one of these vasculitides during the study period and living in the catchment area at the time of diagnosis were included.
Exclusion criteria
Patients were excluded if they had secondary vasculitides, e.g. vasculitides secondary to rheumatoid arthritis, systemic lupus erythematosus (SLE) or other connective tissue diseases, or secondary to viral diseases or associated with malignant disease. Patients who were not residents of the catchment area at the time of diagnosis of PSV were also excluded.
Ethics
Approval for the study was obtained from the ethics committees of the Universities of Lübeck and Freiburg. The study was also approved by the data protection agencies of the Federal States of Schleswig-Holstein and Baden-Württemberg.
Statistics
The annual incidence rates for 1998 and 1999 were calculated as the number of newly diagnosed cases of PSV per 1 000 000 population for all PSVs and for each type of PSV in northern and southern German catchment areas. We also calculated gender-related incidence rates and age-related rates for the population aged 50 yr or older. Calculations were based on the population statistics of 1998. Ninety-five per cent confidence intervals (CI) were calculated for the incidence rates on the basis of the Poisson distribution. Capturerecapture methods were performed to estimate the true accuracy of registration of vasculitides in northern Germany. Population estimates were calculated assuming independence of the three sources of data (hospital departments, departments of pathology and laboratories).
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Results
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For the north, a total of 340 patients were identified initially as having PSV. Fifty-seven of them were finally excluded because the diagnosis of vasculitis had been made before 1998, they were not living in the catchment area at the time of diagnosis, or they turned out to have a disease other than PSV, e.g. a secondary type of vasculitis. Thus, in the north this study included 151 and 133 cases of PSV diagnosed in 1998 and 1999 respectively (Table 2
). In the south, 31 patients failed the inclusion criteria. The number of patients fulfilling the inclusion criteria was 103 in 1998 and 86 in 1999.
The mean frequency of registration per case was 2.0 (range 14). The frequency of ANCA testing in the reference laboratory was similar in the north and south (47 and 48% respectively of all patients). With the capturerecapture method, the maximum likelihood estimate for the total number of cases was 386 for both 1998 and 1999 (north Germany). The three sources of data (clinical departments, departments of pathology and the laboratories) were taken into consideration for this calculation. In summary, 73% of all cases would have been registered.
Characteristics of all PSV cases in northern and southern Germany
North.
There were 151 cases of newly diagnosed PSV in 1998 (66 men and 85 women), 134 in 1999 (55 men and 75 women) (information on gender was missing for three patients) (Table 2
and Fig. 2
). The most frequent type of PSV was GCA (n=45) in 1998 and HSP (n=28) in 1999. Twenty-nine patients had ANCA-associated PSV in 1998 and 21 of these had WG. In 1999, 27 patients had ANCA-associated PSV, 17 of them WG. For details of the number of cases, median age at diagnosis and the gender distribution, see Table 2
.

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FIG. 2. All identified cases of PSV in the north German area over the study period of 2 yr. (A) Males. (B) Females.
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South.
In 1998 there were 103 cases of newly diagnosed PSV (50 men and 53 women) and in 1999 there were 86 cases (39 men and 47 women) (Table 2
and Fig. 3
). The most common type of PSV was HSP in 1998 (n=26), followed by GCA (n=22). In 1999, the most frequent PSV was GCA (n=22), followed by CLA (n=15) (Table 2
). In the south, there were 17 cases of ANCA-associated PSV in both years, 12 and 11 of them respectively with WG.

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FIG. 3. All identified cases of PSV in the south German area over the study period of 2 yr. The numbers 77, 78, and 79 are the zip-codes of the regions. (A) Males. (B) Females.
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In summary, for all PSV entities we found no relevant differences between north and south with respect to median age at diagnosis or gender distribution.
Incidence rates in north and south Germany
In the north, the overall incidence of all PSVs (cases/yr/1 000 000 inhabitants) was 54 (95% CI 3968) in 1998 and 48 (95% CI 3461) in 1999; in the south it was 48 (95% CI 3461) in 1998 and 41 (95% CI 3250) in 1999 (Table 3
). The incidence rate of ANCA-associated PSV was 11 and 9.5 in 1998 and 1999 respectively in the north, and 9 and 7 in the south. Among ANCA-associated PSVs, WG was the most frequently diagnosed type, with incidence rates of 8 and 6 in the north and 6 and 5 in the south. For further details see Table 3
.
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TABLE 3. Incidence rates [cases/yr/1 000 000 inhabitants (95% CI)] from the German vasculitis register for PSV in north and south Germany in 1998 and 1999
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Age-related incidence rates
PSV was two to five times more common in people aged 50 yr or older compared with people younger than 50 yr in both north and south Germany (Table 4
). In the north, the incidence (cases/yr/1 000 000 inhabitants) of all PSVs in people younger than 50 yr was 20.3 in 1998 and 24.8 in 1999 vs 114 and 87 respectively in people 50 yr and older. In the south, the incidence rates were 27.6 and 21.9 for people under 50 yr compared with 91.1 and 75.5 for people over 50 yr. The increase in the incidence of PSV with age was observed in both sexes (Table 4
). For both regions, we found 36 cases (1998) and 42 cases (1999) in children aged 16 yr and younger (66 of them with HSP and eight with Kawasaki syndrome). This resulted in incidence rates of 39.7 in 1998 and 46.3 in 1999 (Table 4
).
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TABLE 4. Age- and gender-related incidence rates [cases/yr/1 000 000 inhabitants (95% CI)] from the German vasculitis register for PSV in Germany for 1998/1999
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Gender-related incidence rates
The overall incidence rates of PSV were similar in men and in women and between north and south (Table 4
). Furthermore, for all PSVs there were no gender differences in incidence in either the younger or the older populations. However, the incidence of GCA in women aged 50 yr and older was twice that in men of the same age.
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Discussion
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This is the first population-based prospective study on the incidences of all types of PSV as defined by the 1992 CHC [2] in a stable, large population (nearly 5 000 000). Previously published data on the period prevalence of PSV in north and south Germany [21] revealed significant differences in prevalence between rural and urban regions as well as between the north and the south, and prompted us to establish a prospective vasculitis register on 1 January 1998. Over a period of 2 yr, we identified 473 patients as having a PSV. The overall incidence was between 41 and 54 cases/yr/1 000 000 inhabitants, without relevant differences between north and south. The literature lacks data on the overall incidence of PSV. The present results indicate an incidence similar to that of SLE [22] (Table 5
). Interestingly, in a previously published epidemiological study [21] we found that the prevalence of PSV resembled that of SLE [22]. PSV has an incidence more than twice that of other autoimmune diseases, such as systemic sclerosis [23, 24], IgA glomerulonephritis [25] and multiple sclerosis [25]. For further details of the incidences of PSV and other autoimmune/systemic diseases, see Table 5
.
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TABLE 5. Incidence rates (cases/yr/1 000 000 inhabitants) of other autoimmune/systemic diseases compared with PSV in Germany
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Except for GCA, data are available on the epidemiology of other PSV entities, e.g. ANCA-associated PSV [69]. However, these studies either employed heterogeneous case-finding methods or were hospital-based studies that took their data from referral centres or covered only small regions. Thus, although their study periods were conspicuously longer than that of our study, they were able to recruit only a small number of patients [69]. The Norwegian study, for example, covered a period of over 15 yr but recruited only 55 WG patients [8]. The British study, covering a period of 11 yr, found only 48 WG patients, and the Spanish study, also over 11 yr, included only 11 WG patients [9]. The present study, by contrast, covered only 2 yr but documented 61 WG patients. During the period covered by the other European studies, new criteria for the classification and definition of the various forms of PSV were established. The diagnostic procedure for PSV has also undergone fundamental change over the past 10 yr, with a consequent increase in the diagnosis of mild or abortive forms of WG and the establishment of ANCA testing as a routine test. With respect to ANCA-associated PSV, our study revealed incidence rates of between 8 and 10 cases/yr/1 000 000 (Table 6
) vs 18 in the UK and Spain [the two latter studies, however, included (classical) PAN]. Besides methodological differences, the criteria used for classification of PSV have a major influence on epidemiological data, such as data for MPA and (classical) PAN [26]. Thus, the present study included all PSVs as defined by the 1992 CHC [2]. Unlike the ACR 1990 classification criteria [1], the CHC definitions incorporate immunological and immunohistochemical findings and distinguish clearly between MPA and PAN. Moreover, with regard to cutaneous vasculitides, the CHC definitions make a clearer distinction between CLA and HSP than the ACR criteria [27]. However, our patients with GCA, WG, CSS and HSP fulfilled both the 1992 CHC definition and the ACR criteria. The ACR criteria do not include MPA and CLA as distinct entities.
Whereas in our study (6372%) and in the British study (53%), WG was the most frequent of the ANCA-associated PSVs (WG, CSS and MPA), in Spain the incidence of MPA (66%) was more than twice that of WG (28%) [9]. Unlike our population-based study, which included nearly 5 000 000 habitants, the Spanish study drew on a referral centre serving a small region with 250 000 inhabitants. The importance of the case-finding methods in epidemiological studies of rare diseases such as PSV was demonstrated by an earlier Swedish study involving cases of small vessel vasculitides. In that study, from a department of nephrology, Tidman et al. [4] only considered in-patients from a department of nephrology. They, too, found more patients with MPA (n=70) than with WG (n=19). In our study, as well as in other population-based studies [7, 9], WG was much more common than MPA. For WG we found an incidence of new cases of between 5 and 8/yr/1 000 000 inhabitants (Table 3
). Our incidence rates for WG were lower than those in the UK and Norway but higher than those in Spain (Table 6
). This result could reflect a real regional difference between northern and southern Europe, similar to that found for GCA. Another explanation could be that the Spanish study only considered adults aged >20 yr. However, our data for WG in adults aged >20 yr show incidence rates for WG in the north of 10 and 8 in 1998 and 1999 respectively, i.e. rates higher than those for the total population. Thus, the omission in the Spanish study of individuals aged <20 yr cannot explain the different incidence rates for WG between the two studies. As shown earlier, regional differences were also found in the prevalence of PSV between rural and urban regions [21]. These differences are similar to those described for GCA in a Danish study, which found GCA to be more prevalent in cities than in rural areas [28]. It is striking that the GCA in this Danish study occurred in close temporal association with mycoplasma epidemics, which were also more frequent in urban than in rural regions. However, in the present study we found no clustering of GCA or other PSVs in cities in either the northern or the southern mixed rural/urban catchment areas. A study period of only 2 yr, however, could be too short to detect such clustering. The need to clarify this point is one of several reasons why the German vasculitis register is to be continued.
We found no differences in the incidence rates of all PSV entities between north and south. In addition, the demographic data of the general population and of the PSV patients (gender distribution and median age at diagnosis) revealed no differences between the two regions. However, it is remarkable that the median age at diagnosis of our WG patients was about 60 yr over the whole observation period both in the north and the south, whereas in former large WG cohorts, recruited 1030 yr earlier, the median age at diagnosis was in the mid-forties [2932]. The median age at diagnosis of WG patients in the present study was higher than reported for previous large WG cohorts. In addition, the interval between the first symptom attributable to WG and the diagnosis of WG was conspicuously shorter in the present study (median 3 months, range 048 months) than in older cohorts (9 months, range 0288 months) [32]; in the National Institutes of Health cohort of Hoffman et al. [29] it was 15 months. Compared with our own earlier WG cohort of 155 patients [32], the present study found a marked increase, of almost 15 yr, in the age at diagnosis of WG patients, although the time between first symptoms and diagnosis was less by one-third. This could possibly be explained by the increased attention now being paid to these diseases, especially in older people. For the Norwegian WG patients [8], recruited between 1984 and 1998, the median age at diagnosis over the whole study period was 50 yr, whereas the Spanish WG patients [6, 9] were nearly 60 yr old at diagnosis, an age similar to that of our WG patients. No information is available on the age at diagnosis of the WG patients in the 11-yr British study [7, 9]. However, an earlier study by the same group [12], involving the same catchment area and possibly some of the same patients, identified 21 WG patients between 1988 and 1994 with a median age at diagnosis of 62 yr (range 3387 yr), whereas the median time from onset to diagnosis was only 2 months (range 0.540 months).
The present study has certain limitations. The incidence rates for GCA, and possibly also for CLA, appear to be too low when compared with other epidemiological studies involving these diseases alone [10, 19, 27, 33]. The comparatively mild vasculitis entities GCA and CLA are often diagnosed by general practitioners without taking biopsies or referring patients to a specialized physician or hospital. Such cases could have been missed in our study. This fact reflects the results we obtained by the capturerecapture method, which indicated that 73% of the cases were registered. However, a major assumption for capturerecapture methods is that the sources are independent. As there is partial dependence between clinical departments and departments of pathology and between clinical departments and laboratories, and because this dependence may be positive or negative, it is likely that the true population will be over- or underestimated by this method. However, the main goal of our study was to determine the incidence rates of all PSVs in north and south Germany in a large population-based study. Because of the similar incidence rates in the north and south both for the whole group of PSVs and for each entity, and because of the similarities in patient characteristics, population structure and frequency of registrations per case, the present study reveals true, valid data on the epidemiology of PSV in Germany.
In summary, the first results from this population-based vasculitis register, encompassing two large regions in the north and south of Germany, have revealed PSV incidence rates of between 41 and 54 cases/yr/1 000 000 inhabitants over a period of 2 yr, without significant differences between north and south. Compared with other European countries, the incidence of ANCA-associated PSV in Germany was lower than in the UK, and our incidence rates for WG were lower than those in the UK and Norway but higher than that in Spain. Whether these results reflect real differences between northern and southern Europe, possibly caused by differences in exposure to exogens, or whether they simply reflect differences between our case-finding methods and the methods used by smaller regions or referral centres, remains unclear. In any event, the German vasculitis register will be maintained. Moreover, for all WG patients in the register, a casecontrol study is currently under way to study the role of exposure to exogens in the pathogenesis of their disease.
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Acknowledgments
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The authors would like to thank Mrs Claudia Möck, Mrs Martina Rosenbladt and Mr Tim Uhlenkamp (Cancer Register, Schleswig-Holstein) for excellent assistance. This work was supported by grants from the German Federal Minister for Education, Science, Research and Technology (01 VM 9306).
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Notes
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Correspondence to: E. Reinhold-Keller, Poliklinik für Rheumatologie der Universität zu Lübeck, Rheumaklinik Bad Bramstedt GmbH, Oskar-Alexander-Strasse 26, D-24 576 Bad Bramstedt, Germany. 
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Submitted 11 June 2001;
Accepted 9 November 2001