Epidemiology in inflammatory bowel disease : Unanswered questions-European perspective

V BINDER, Epidemiology in inflammatory bowel disease: Unanswered questions European perspective. Can J Gastroenterol 1993;7(2):139-141. Several European epidemiological studies have shown similar patterns for Crohn's disease, demonstrating an increase in incidence over the past 30 years. It has, however, not been revealed whether the apparent differences in incidence, with a much higher value in the north than in the south of Europe, are real. A European multicentre study, comprising 20 centres, is being carried out over the next three years, using well defined and equal diagnostic criteria. From published epidemiological studies, it appears that the disease entities for ulcerative colitis and Crohn's disease have remained practically unchanged during the past two decades, as regards clinical appearance at diagnosis. The different pattern in incidence of ulcerative colitis (almost steady) and Crohn's disease (steep increase) supports the concept of two different diseases. The steep increase in occurrence of Crohn's disease points to an external factor in the etiology of the disease.

A partir des etudes epidemiologiques publiees, ii scmble que les cas de colice ulcereuse et de maladie de Crohn sont pour ainsi dire demeurcs inchanges au cours des deux demieres decennies pour ce qui est de l'aspect cliniquc au moment du diagnostic.Le mode d'incidence different <le la colite ulcereuse (presque constant) et de la maladie de Crohn (augmentation nette) appuie la these de deux entires cliniques distinctes.L'augmentation nette des cas de maladie de Crohn suppose la participation d'un facteur exogene clans l'etiologie de la maladie.ease has increased in almost all European countries during the past 20 to 30 years.The increase has been almost parallel in different stuuies, but displaced in time.Over the past 10 years a few studies have shown that the incidence of Crohn's dbease is beginning ro level off.For example, two recent stud ies from Sweden ( 1,2) have shown a stable incidence, but at a very high level of about six per 100,000 population.

Department of Medical Gascroemerology
The pattern over time b less clear for ulcerative coli tis, some studies showing an increase in incidence, with the majority indicating an almost stable incidence over the past 20 years.
In Europe a correlation has been found in different places between the frequencies of the two diseases, with a I :2 ratio of occurrence of Crohn's disease to ulcerative colitis.It appears that the highest incidence rates are in Norway (3,4) and Sweden (1 ), fo llowed by Denmark (5,6), then Holland (7,8) and finally Italy (9, 10) (Figure 1 ).
A hypothetica l north-south ax is has been proposed for inflammatory bowel disease (IBO), with the highest incidence in northern Europe anJ lowest in the south.This hypothesis is supported by the ex isting incidence data.The basis fo r epidemiological studies is a complete and totally regional group of patients, which implies that the organization of the health care system in the area studied is of importance.In   Regarding sex distribution, ulcerntive colitis seems to affect both sexe~ almost equally.However, Crohn 's disease has been found in some studies to be mon: frcquem in women, although other tudics have shown the d isease to he distributed evenly between rhe sexes.
In a population-based study from Copenhagen county, carricJ out over 26 years (5,6), an increase in the incidence of Crohn's disease from less than one per 100,000 inhabitants tu abou t four per 100,000 inhabitants, was found, with a constant fcmalc:male ratio of 1.4: L. The incidence of ulcerative coli tis was higher in women in the early part of the study period, and has been equal in the 1970s and '80s.The mean incidence was 8. l per 100,000.
T he clinical Jara from five recent publications from Florence, Leyden, Copenhagen, Uppsala and western Norway a rc shown in Table l.It appears chat, in the Scandinav ian countries, about 40% of the patients have proctosigmoiditis at diagnosis.The risk of proximal progression of the disease has been studied, and the resu lts from Scorland ( 11) and preliminary results from the author's study (unpublished data) are in accordance.In the first year after diagnosis, 12% of the cases progressed proximally, and <luring the fo llowing 10 years a steady rate of 6% per year had more extensive disease.In half of the patients the progression occurred as fa r as the sple nic.flexure, in a quarter to the hepatic flexure a nd 111 the rcmamder to the cecum .
These finJ ing~ ~rrongly surporr rhc view that proctit11; is not a separate disease entity from ulcerative colitis.It will be important to determine whether disease locali zation is comparable between southern and northern European centres.One possible factor that Ct)uld account for the hypotheucal northsouth axis coulJ he that the diagnostic threshold in the south 1s higher, anJ the true incidence of lBD is unJeres-timate<l.
The clinical data from six recent epidemiological studies of Crohn's Jiseasc arc shown in Table 2.There are some variances in distributinn of the three main locali:auons -ileocolonic, Crohn's disease incidence over the past 25 years in Denmark h as been equally pronounced in all three areas.
The proportion of cases rresenting with high activity of disease ha~ increased slightl y over time, thu, indicating not only increasing incidence but also more aggres,ive disease.

Figure 1 )
Figure 1) Ccmdmicm between incidence of 11u:aacii1 i.' colitis and Cmlm 's disea.se Epidemiology ofCrohn's disea,c in the region ofLciJen, The Ncrherlands.A study population from 1979 to l 983.Gasrroemerolog-y l 987;93:966-74 8. Shivananda S, Pena AS, Mayberry JF, Ruitenbcrg EJ, Hoedemackcr PJ.Epidemiology of proctocol1t1s m the region of Leiden, The Netherland,.Scand J Gastrocnterol l 987;22:993-1002.CAN J GASTROENTEROL Vrn 7 No 2 FEBRUARY 1993 Epidemiology In IBD: Unanswered questions from Stockholm, whereas orher studies have not been ahle to find such specifi-Lally exposed group,.The studies thus await further confirmation.In c.onclusinn, from the existing cridemiolog1cal Jata it arrears that the two disease entittes have remained practically unchanged Juring the past 20 years, a, regards clinical appearance at diagnosis.The different pattern in incidence of ulcerative colitis and Crohn \ disease support the concept of two different Jiseases.Finally, the steep increase in incidence of Crohn\ disease roints to an external factor in the etiology of the disease.