RHEUMATOLOGY
Rheumatology 2013;52:304–310
doi:10.1093/rheumatology/kes249
Advance Access publication 25 September 2012
Original article
Incidence, prevalence and clinical characteristics
of Behçet’s disease in southern Sweden
Aladdin Mohammad1,2, Thomas Mandl1,2, Gunnar Sturfelt1,2 and
Mårten Segelmark3,4
Abstract
Objective. To study the incidence, prevalence and clinical characteristics of Behçet’s disease (BD) in a
defined population in southern Sweden.
Methods. The study area consists of three health-care districts with an adult population (515 years) of
809 317 on 1 January 2011 (25% of non-Swedish ancestry), situated in Skåne, the southernmost county in
Sweden. Patients were identified using clinical registries in all the five hospitals within the study area. Only
patients fulfilling the International Study Group criteria for diagnosis of BD were included.
CLINICAL
SCIENCE
Results. Forty patients (13 women) fulfilling the diagnosis criteria for BD (70% of non-Swedish ancestry)
were identified. The point prevalence of BD on 1 January 2011 was 4.9/100 000 adults (95% CI 3.4, 6.5)
and was higher among the population of non-Swedish ancestry (13.6 vs 2.0/100 000, P < 0.001), and
higher among men (6.8 vs 3.2/100 000, P = 0.019). There were 20 incident cases (diagnosed in Sweden
between 1997 and 2010). The annual incidence rate was 0.2/100 000 adults (95% CI 0.1, 0.3) and was
higher among the population of non-Swedish ancestry (0.6 vs 0.1/100 000, P < 0.001). The incidence was
0.3/100 000 adults in men and 0.1/100 000 in women, P = 0.143. During the course of the disease, 100% of
the patients developed oral ulceration, 80% genital ulcers, 88% skin lesions, 53% eye disease, 40%
arthritis/arthralgia and 20% venous thrombosis.
Conclusion. The prevalence of BD is higher in Sweden than previously reported, mainly due to immigration. The incidence of BD remains elevated for immigrants from high-prevalence regions even long after
settling in Sweden.
Key words: incidence, prevalence, Behçet’s disease, population-based study, epidemiology.
Introduction
Behçet’s disease (BD) is a chronic inflammatory disease
of unknown aetiology characterized by recurrent oral and
genital ulceration and a variety of systemic manifestations, most of them believed to be due to vasculitis. The
International Study Group (ISG) for BD has published
diagnostic criteria that are widely used in epidemiological
1
Department of Clinical Sciences, Section of Rheumatology,
Lund University, Lund, 2Department of Rheumatology,
Skåne University Hospital, Lund, 3Department of Nephrology
UHL, County Council of Östergötland, Linköping and 4Department
of Medical and Health Sciences, Linköping University, Linköping,
Sweden.
Submitted 18 April 2012; revised version accepted 3 August 2012.
Correspondence to: Aladdin Mohammad, Department of
Rheumatology, Skåne University Hospital, Lund SE-221 85, Sweden.
E-mail: [email protected]
studies [1]. BD has a distinct geographical distribution
with high prevalence in regions along the old trading
route called the Silk Route, connecting the
Mediterranean area with East Asia [2]. The prevalence of
BD has been reported to be 0.64/100 000 in the UK, 1.53
in Portugal, 2.26 in Germany, 5.2 in the USA, 7.1 in
France, 13.5 in Japan, 15.2 in Israel, 17 in Iraq, 20 in
Saudi Arabia, 80 in Iran and as high as 421 in Turkey
[2–10]. The epidemiology of BD in Sweden is largely unknown. Ek and Hedfors [11] reported on 12 cases from
Sweden, 6 of them immigrants. Based on these cases, the
prevalence of BD in Sweden was estimated to be 1.18/
100 000 [11].
In low-prevalence countries, lower rates have been reported in populations of European ancestry compared
with immigrants from areas where the disease is highly
prevalent [5, 12]. A higher rate of immigration and possibly
! The Author 2012. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: [email protected]
Incidence and prevalence of BD in Sweden
increasing awareness among physicians could, at least
partially, have influenced the increased prevalence of BD
in Germany from 0.65 in 1984 to 2.26/100 000 in 1994 [13].
There are few studies reported on the incidence of BD,
the rate per 100 000 has been estimated to be 0.24 in Italy,
0.38 in the USA and 1.0 in Germany [3, 4, 12]. The disease
usually affects people in the second to third decades of
their lives [14]. The sex distribution in BD seems to vary
between geographical areas; there is clear male predominance in studies from Turkey and the Middle East,
whereas the male : female ratio is close to one in
European countries [14]. BD is associated with high morbidity rates with eye involvement often leading to the most
debilitating outcome, especially in young men. In some
studies, the risk of permanent loss of useful vision within
10 years has been reported to be as high as 30–65% [15].
Despite the differences in prevalence of BD among different ethnic groups, a number of previous studies have reported no or only few variations in the clinical
characteristics of BD in different regions and ethnic
groups. In northern Israel a higher rate of erythema nodosum and deep vein thrombosis and a tendency towards a
higher rate of posterior uveitis was found among Arab
patients, whereas Druze patients had significantly less
severe disease [6]. In Germany, the clinical expression
of the disease was similar among Turkish and German
patients with the exception of ocular lesions, which were
significantly more prevalent among Turkish patients [13].
No such comparison has been made among different
ethnic groups in northern Europe.
The aims of this study were to: (i) estimate the annual
incidence rate and point prevalence of BD in a
well-defined multi-ethnic population in southern Sweden;
(ii) to compare the epidemiological characteristics of BD
with other reported data from other regions in the world;
and (iii) to describe the clinical and demographic characteristics of BD in southern Sweden.
Patients and methods
Study design
This is a population-based study of the incidence and
point prevalence of BD in southern Sweden. For the incidence study; all newly diagnosed cases of BD between
1997 and 2010 for patients of Swedish ancestry were
included, whereas patients of non-Swedish ancestry
were included only if the diagnosis of BD was made a
minimum of 3 years after immigration to Sweden. For
the prevalence estimates all patients fulfilling ISG criteria
of BD who were living in the study area on 1 January 2011
were included. The numerator for the incidence rate estimates was the number of patients diagnosed with BD
after 1997. The denominator population for the incidence
rates is the total adult population in the middle of the study
period, December 2004. For the prevalence estimates, the
numerator was all patients with BD who were living in the
study area at the date of prevalence estimates. The denominator was the total adult population in the study area
on 31 December 2010.
www.rheumatology.oxfordjournals.org
Study area and population
The study area consists of three health-care districts in
Skåne, the southernmost county in Sweden (Fig. 1). The
adult population (515 years) on December 2010 was
809 317 (10% of the adult population in Sweden) and
206 381 (25%) were of non-Swedish ancestry [16]. The
adult population in the study area increased by 108 266
inhabitants (13.3%) from 1997 to the end of 2010. In the
middle of the study period (December 2004), the adult
population was 743 868 [154 659 (21%) were of
non-Swedish ancestry]. Females made up 50.8% of the
study population. The study area is about 5334 km2 (1.2%
of the total area of Sweden) and is divided into 22 municipalities, the largest being the cities of Malmö, Helsingborg
and Lund. Non-Swedish ancestry is defined as a person
born abroad or with two foreign-born parents. Region
Skåne is a regional public body with administrative and
financial responsibility for the health of the inhabitants,
and for providing medical and dental services. The study
area is served by five hospitals, all run by Region Skåne:
Skåne University Hospital in Lund and Malmö, Trelleborg
Hospital, Landskrona Hospital, Helsingborg Hospital and
Ängelholm Hospital.
Case ascertainment
Clinical records, including hospital discharge records and
databases listing outpatient clinics, were searched using
the International Classifications of Diseases (ICD)-10
codes of BD M35.2 for the period 1998–2010 and the
corresponding ICD-9 codes for 1997. The case retrieval
was part of a more extensive case retrieval including a
search in a large number of departments to study other
vasculitic diseases in our area and is described in detail
elsewhere [17]. In short, during the time period between
1997 and 2003, searches were done at the databases of
the following departments: Rheumatology, Nephrology,
Dermatology, Infectious Diseases, Ophthalmology and
General Internal Medicine (including Pulmonology,
Cardiology and Gastroenterology). We also performed a
search in the database of the Department of Pathology,
Lund University Hospital, using the free-text term of vasculitis on the entire text of all pathology reports. All potentially eligible patients were re-identified at the databases
at the Departments of Rheumatology, Ophthalmology and
Nephrology. Therefore, the sources for case retrieval between 2003 and 2010 were limited to the Departments of
Rheumatology, Nephrology and Ophthalmology at Skåne
University Hospital in Lund and Malmö. For all other hospitals within the study area, searches were carried out at
the Departments of Internal Medicine (including all the
medical subspecialties) and Ophthalmology. In addition,
private rheumatology practices in the studied area were
also asked if they treated patients with BD. A detailed
case record review was done by two of the authors
(A.M. and T.M.). Only patients fulfilling the criteria for diagnosis of BD according to the ISG criteria for BD [1] were
included in the study. In borderline cases, a consensus
was reached by the authors. Cases with isolated genital
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Aladdin Mohammad et al.
FIG. 1 Map showing the county of Skåne in southern Sweden and the study area (shaded).
or oral ulcers for which there was not enough clinical data
to fulfil the ISG criteria of BD were not included in this
study.
Data collection
The following data were collected: age, gender, original
nationality and ethnic background, date of immigration to
Sweden, diagnosis delay (the time elapsed in months from
the first possible symptoms of BD to the date of diagnosis)
and clinical features occurring at any time during the disease course.
Statistical analysis
Statistical analysis was performed using the Statistical
Package for the Social Sciences, SPSS 18.0 for
Windows (SPSS Inc., Chicago, IL, USA). The differences
between groups were compared by means of the
non-parametric Mann–Whitney U-test and chi square
(2) test where appropriate. P-values of 40.05 were considered to be statistically significant. The 95% CI was
calculated assuming a Poisson distribution of the
observed cases. Data are presented as median and
range unless otherwise stated. The study was approved
by the local Ethics Committee at the Faculty of Medicine,
Lund University (LU 283-02 and 2010-517).
Results
The patients
A total of 40 patients (13 women) fulfilling the diagnosis
criteria for BD were included in the study. Twenty patients
306
were incident cases diagnosed during the study period
between 1997 and 2010.
Twenty-eight patients (28/40; 70%) were of nonSwedish ancestry (six women). One patient was born in
Sweden of parents from a southern European country; for
the remaining 27 patients; the areas/countries of origin
were as follows: the Middle East (n = 15), Africa (n = 2),
East Asia (n = 2), Turkey (n = 2) and central and eastern
Europe (n = 6). Data in the case records on the year of
immigration were only available for 24 patients. Six patients had been diagnosed with BD before their immigration to Sweden. For the remaining patients (n = 18), the
median time elapsed between immigration to Sweden
and the diagnosis of BD was 6.5 years (range 1–35
years). There was no case record documentation on
date of immigration of three patients. These patients
(three men) were not included in the incidence estimates
as it is not clear when they started getting their BD symptoms in relation to immigration to Sweden.
The male : female ratio among all patients was 2.07;
among patients of non-Swedish ancestry the male : female ratio was 3.66 compared with 0.71 among patients
of Swedish ancestry. The median age at diagnosis for all
patients was 30.5 years (11–53 years): 30 years (11–47
years) for patients of non-Swedish ancestry compared
with 34.5 years (14–53 years) for Swedish patients
[P = not significant (NS)]. The median age at the date of
point prevalence was 42.5 years (16–66 years) for all patients: 41.5 years (17–56 years) for patients of
non-Swedish ancestry compared with 54 years (16–66
years) for patients of Swedish origin (P = NS). The
www.rheumatology.oxfordjournals.org
Incidence and prevalence of BD in Sweden
median time of diagnosis delay was 32 months (0–96
months) for all patients: 36 months (0–96 months) for patients of non-Swedish ancestry compared with 30 months
(2–72 months) for patients of Swedish origin (P = NS). The
median time of disease duration (time from diagnosis to
the date of prevalence estimates) was 119 months (1–379
months) for all patients: 118 months (1–319 months) for
patients of non-Swedish ancestry compared with 157
months (23–379 months) for patients of Swedish ancestry
(P = NS).
TABLE 1 Sex- and age-specific incidence ratesa of BD in
southern Sweden
No. of
cases
All patients
20
Swedish ancestry
6
Non-Swedish ancestry
14
Sex-specific incidence rate
Men
All
13
Swedish ancestry
2
Non-Swedish ancestry
11
Women
All
7
Swedish ancestry
4
Non-Swedish ancestry
3
Age-specific incidence rate, years
15–24
6
25–34
8
35–44
3
45–54
3
555
0
Clinical characteristics
The clinical features occurring during the entire course of
the disease are shown in Table 3 and Fig. 2. There were
no differences in the clinical features between patients of
non-Swedish ancestry compared with those of Swedish
ancestry (data not shown). The most common skin lesion
was pustulosis (n = 16), followed by folliculitis (n = 11) and
erythema nodosum (n = 10). The most common eye involvement was posterior uveitis (n = 10), followed by anterior uveitis (n = 7) and retinal vasculitis (n = 4). Only one
patient lost her vision totally in one eye. In eight patients,
the diagnosis of vasculitis was confirmed by histopathology from lesion from the oral or genital area. No patients
developed neurological disease.
Incidence
(95% CI)
0.2 (0.1, 0.3)
0.1 (0.0, 0.1)
0.6 (0.3, 1.0)
0.3 (0.1, 0.4)
0.0 (0.0, 0.1)
1.0 (0.4, 1.7)
0.1 (0.0, 0.2)
0.1 (0.0, 0.2)
0.3 (0.0, 0.6)
0.4 (0.1, 0.7)
0.5 (0.1, 0.8)
0.2 (0.0, 0.4)
0.2 (0.0, 0.4)
0 (0.0, 0.0)
a
Incidence rate/100 000 adults.
Annual incidence rate
Twenty patients (seven women) fulfilled the study definition of incidence estimates (Table 1). Six patients were of
Swedish ancestry. Of the 28 patients of non-Swedish ancestry, 13 (46%) were diagnosed at least 3 years after
immigration to Sweden [median time 11 years (3–35
years)] and 1 born in Sweden with Italian parents. The
annual incidence rate for all patients was 0.2/100 000
adults (95% CI 0.1, 0.3); 0.6 (95% CI 0.3, 1.0) for patients
of non-Swedish ancestry and 0.1 (95% CI 0.0, 0.1) for
patients of Swedish ancestry (P < 0.001). The sex-specific
incidence is shown in Table 1. No statistically significant
difference was found regarding the incidence rate among
the men and the women: 0.3 (95% CI 0.1, 0.4) vs 0.1 (95%
CI 0.0, 0.2); P = 0.143. The highest age-specific incidence
was in the age group of 25–34 years: 0.5 (95% CI 0.1, 0.8).
No cases were diagnosed with BD in the age group of
555 years.
Point prevalence
At the date of point prevalence estimates (1 January
2011), a total of 40 patients fulfilled the ISG diagnostic
criteria for BD resulting in a point prevalence of
4.9/100 000 adults (95% CI 3.4, 6.5) (Table 2). The prevalence of BD was significantly higher among subjects of
non-Swedish ancestry than among subjects of Swedish
ancestry: 13.6 (95% CI 8.5, 18.6) vs 2.0 (95% CI 0.9, 3.1);
P < 0.001. For the entire study population, the genderspecific prevalence rate of BD was significantly higher
among men than women: 6.8 (95% CI 4.2, 9.4) vs 3.2
(95% CI 1.4, 4.9); P = 0.019. Similarly, in patients of
non-Swedish ancestry, the prevalence among men was
significantly higher than among women: 21.5 (95% CI
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12.5, 30.5) vs 5.8 (95% CI 1.2, 10.4); P = 0.002.
However, there were no statistically significant differences
in prevalence between men and women of Swedish
ancestry 1.7 (95% CI 0.2, 3.2) vs 2.3 (95% CI 0.6, 4.0);
P = 0.614.
Discussion
This is a population-based study from a large well-defined
population in southern Sweden on the epidemiology and
clinical characteristics of BD. In this study, we compare
prevalence rates, demographics and clinical characteristics in our area with a number of studies selected to represent different geographical areas from the Middle East,
through southern and central Europe ending in northern
Europe and North America (Table 3).
We report a prevalence of 4.9/100 000, which is substantially higher than a previous estimate of 1.2 based on
a small case series from 1993 [11]. The figure is in the
same range as those reported from the USA and in between figures from Germany and France (Table 3).
Immigrants constituted the majority of cases in our
study; the prevalence among individuals of non-Swedish
ancestry was 7-fold higher than in those classified to be of
native Swedish origin. Studies on BD in Germany and
France have shown similar epidemiological characteristics
[5, 12]. However, in a population-based study from Italy all
18 patients were of Italian descent [3]. When analysing the
origin of the patients, it is of interest to note that 19 (68%)
of the 28 non-Swedish patients were from highprevalence areas, whereas, in general, immigrants from
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Aladdin Mohammad et al.
TABLE 2 Sex- and age-specific point prevalencea of BD in southern Sweden
No. of cases
Prevalence (95% CI)
40
12
28
4.9 (3.4, 6.5)
2.0 (0.9, 3.1)
13.6 (8.5, 18.6)
27
5
22
6.8 (4.2, 9.4)
1.7 (0.2, 3.2)
21.5 (12.5, 30.5)
13
7
6
3.2 (1.4, 4.9)
2.3 (0.6, 4.0)
5.8 (1.2, 10.4)
4
8
10
11
7
3.1
5.9
7.4
9.0
2.5
All patients
Swedish ancestry
Non-Swedish ancestry
Sex-specific point prevalence
Men
All
Swedish ancestry
Non-Swedish ancestry
Women
All
Swedish ancestry
Non-Swedish ancestry
Age-specific point prevalence, years
15–24
25–34
35–44
45–54
555
(0.1,
(1.8,
(2.8,
(3.7,
(0.6,
6.1)
9.9)
11.9)
14.3)
4.3)
a
Point prevalence/100 000 adults.
TABLE 3 Epidemiological, demographic and clinical data of BD in southern Sweden compared with selected studies
from different geographical areas in the Middle East, Europe and North America
Country of study [reference no.]
No. of patients
Total population
Prevalence/100 000
Male : female ratio
Age at diagnosis, mean (S.D.), years
Clinical manifestations, %
Oral ulceration
Genital ulceration
Skin lesions
Eye disease
Arthralgia/arthritis
Venous thrombosis
CNS involvement
Israel
[6]
Italy
[3]
Germany
[13]
France
[5]
USA
[4]
Sweden
(this study)
112
737 000
15.2
1.11
33 (10.6)
18
486 961
3.8
1
33 (7)
49
2 170 411
2.26
0.88
25 (5–60)a
79
1 094 412
7.1
1.32
33 (10.9)
13
NR
5.2
0.44
31 (9)
40
809 317
4.9
2.07
30.5 (9.9)
NR
68
41
53
70
15
12
100
78
100
56
50
6
11
99
75
76
59
59
NR
12.8b
100
80
90
51
59
NR
10
100
62
85
62
46
15
23
100
80
88
53
40
20
0
a
Median (range). bNeurological features. NR: not reported.
these areas constitute a smaller proportion of the Swedish
immigrant population.
The prevalence of BD in the present study was significantly higher among men than women, but this was not
the case when the analysis was confined to patients of
Swedish ancestry. The sex-specific prevalence figure was
higher among men than women (8.1 vs 6.1/100 000) in
France [5]. Contrary to this, the prevalence was higher
among women than men (6.4 vs 4.2/100 000) in the USA
[4], and almost equal in Germany (2.29 vs 2.22/100 000)
[13]. The male : female ratio in our study is also higher than
reported in studies from Iran [18], Turkey [7] and Israel [6],
308
but comparable to results of studies from Kuwait (3.1) [19],
Iraq (2) [9] and Saudi Arabia (3.4) [20]. There are, however,
important methodological differences in case recruitment
as some studies used population sample-survey methods, while others relay mainly on diagnosis listed in
health-care registries. There always exists a risk of incomplete case findings in both sample-survey and registry
studies, but at different ends on the severity spectrum,
which should be taken in consideration when comparing
the results. Sample-survey methods are not suitable for
BD in regions where the disease is as low as in northern
Europe.
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Incidence and prevalence of BD in Sweden
FIG. 2 Selected clinical features in 40 patients with BD from southern Sweden.
Recurrent fever: a body temperature that exceeds 38 degrees recurrent in different time periods at onset (either reported
by patient or measured at hospital). Biopsy-verified vasculitis: biopsy taken from skin, or oral or genital ulcers showing
vasculitis.
The incidence rates of BD in Italy and the USA were
reported to be 0.24 and 0.38/100 000 respectively [3, 4],
which is within the same range as our finding of 0.20/
100 000. In the present study, we set an arbitrary time
limit of 3 years after immigration for a case to be counted
as an incidence case in Sweden, based on the average
diagnosis delay for patients of non-Swedish origin in this
study. Consequently, the vast majority of the incidence
cases had no symptoms when settling in Sweden, still
the incidence was significantly higher among immigrants
of non-Swedish ancestry compared with the native
Swedish population; no such comparison was reported
in the Italian or the American studies.
The clinical features of our patients were comparable
among patients of Swedish and non-Swedish ancestry,
and the features of our patients were similar to those reported in other studies (Table 3). However, we did not
have any case with neuro-Behçet’s, although this variety
has been reported to constitute between 2.2% and 44%
of the patients in other series [14]. Even though eye involvement was common, only one patient in our study had
complete loss of vision in one eye, which is also lower
compared with other reports.
The large variation in the prevalence of BD in different
parts of the world could be explained by an interaction
between genetic and environmental factors. To a lesser
extent, the results could be even explained by differences
in case identification and case retrieval. Cases in this
study were retrieved by search at the clinical registries
in a large number of departments with specialties covering
all clinical aspects of BD as well as all private rheumatology clinics within the area. However, we could not totally
exclude the possibility of missing a small number of cases
in our area; an inevitable limitation of an epidemiologic
study like ours. Our study has a number of strengths as
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well. It is a population-based study covering a relatively
large multi-ethnic population with a minimum of referral
and selection biases.
The aetiology of BD is unknown, and so is the relative
contribution from genetic and environmental factors.
Some epidemiological observations favour the role of environmental factors; the prevalence of BD among Turks
living in Germany is much lower than in Turkey, and
Japanese people living in Hawaii and the USA do not
seem to develop the disease [15]. In our study, 18 out of
28 (64%) patients of non-Swedish ancestry were diagnosed with BD after their immigration to Sweden, an observation favouring the effect of the genetic rather than the
environmental factors. In a study from a multi-ethnic
suburb of Paris, Mahr et al. [5] found that among individuals of non-European ancestry, the prevalence was similar for those born in France to those who migrated to
France before the age of 15 and those who migrated
later in life. The author’s conclusion was that BD is primarily a hereditary disease. The differences in sex distribution between regions are, however, difficult to explain
from a strictly genetic perspective, but maybe social factors could be contributory agents.
Previously published data and the present study indicate that BD is more common in immigrants from highprevalence areas also long after settlement in low prevalence areas, but still lower than for those remaining in the
high prevalence areas. These epidemiological data could
be explained by a microorganism requiring intimate contact to be transmitted, a situation resembling the case
with EBV or HPV. When children get infected with EBV
they get a non-specific respiratory infection, whereas
young adults may acquire mononucleosis (kissing disease). In a similar fashion, a causative agent for BD
might be widespread among children and give rise to
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Aladdin Mohammad et al.
BD only in genetically predisposed individuals infected in
adulthood. This speculative explanation requires that the
distribution of the causative agent differs between ethnic
groups, and that behaviour and social factors explain differences between the genders in different populations.
In conclusion, this is the first population-based report
on the incidence and prevalence of BD in a relatively large
multi-ethnic population in Sweden. The prevalence of BD
is the highest reported from northern Europe. The incidence and prevalence rates were significantly higher
among people of non-Swedish ancestry even though
most patients developed symptoms many years after
immigrating to Sweden.
Rheumatology key messages
The prevalence of BD in southern Sweden is higher
than previously reported.
. The prevalence and incidence of BD are significantly higher among people of non-Swedish ancestry in southern Sweden.
.
Funding: This study was supported by research grants
from the Swedish Research Council (64X.09487-181),
the Faculty of Medicine, Lund University, the Thelma
Zoégas
Foundation
for
Medical
Research
in
Helsingborg, Sweden and the Swedish Rheumatism
Association (Reumatikerförbundet).
Disclosure statement: The authors have declared no
conflicts of interest.
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