Crohns Disease and the epidemiologic studies of inflammatory bowel disease involve many of the problems encountered in any large population study of chronic disease.
In particular, there are questions of definition differentiation of Crohns disease from other forms of inflammatory bowel disease, including the entire range of infectious colitides, as well as from ulcerative colitis.
The recognition of Crohns disease of the colon as distinct from ulcerative colitis in the past 40 years raises serious concerns about disease incidences reported in older series and about the incidence of complications allegedly associated with Crohns disease versus ulcerative colitis.
The term acute regional enteritis, discussed elsewhere in this monograph, further emphasizes the difficulty in defining the incidence of Crohns disease precisely. In addition, the different diagnostic skills and uneven availability of diagnostic resources around the world undoubtedly account for the variable detection of the disease.
Furthermore, the variable and sometimes insidious onset of Crohn’s disease handicaps precise dating of the onset of illness.
While, on the basis of present evidence, climatic and other geographic factors do not appear causally related to the frequency of inflammatory bowel disease, dietary differences among populations may influence stool composition and frequency as well as the intestinal bacterial flora, all of which might influence the course of Crohns disease, once established, and perhaps also the development of such complications as liver disease or carcinoma of the colon.
The term annual incidence rate refers to the rate of occurrence per 100,000 persons at risk per year. The term prevalence refers to all patients with illness at any point in time per 100,000 persons at risk.
Data relating to the incidence and the prevalence of Crohns disease have been published by several groups in recent years (13-18). It should be noted that the data listed are derived from populations that are largely white and of European origin.
The incidence of ulcerative colitis and of Crohns disease is approximately of the same order of magnitude in different parts of the world. The incidence of Crohns disease, in the past, has been less than that of ulcerative colitis in all the populations reported.
However, the incidence of Crohns disease is increasing generally. The distinctly higher incidence rate reported to the thoroughness of the case search and to a high degree of awareness of the disease in that community, although an unusually high “natural” incidence could not be excluded. These authors eliminated acute regional enteritis from consideration.
Also, they poi during the years of the study, when the incidence disease was strikingly on the increase, the incidence of ulcerative colit fairly constant, mitigating against the likelihood that the increased in Crohn’s disease could be attributable to changes in diagnostics.
In a study of 204 patients with Crohns disease of the colon, twice the number of deaths expected for an age and sex-matched control population. Researchers examining Crohns disease of both small and large bowel, found that the excess mortality was attributable to the effects of the disease itself, to supervening malignancy, or to malignant hypertension secondary to the use of corticosteroid medication.
Using cumulative recurrence rates, noted that the risk of recurrence did not decrease with time; however, their analysis of deaths from Crohns disease suggested that the risk of death decreased with time.
Special risk factors include sex, age, race, ethnicity, geography, and socioeconomic factors. In most series, there is a slight preponderence of ulcerative colitis among women and of Crohns disease among men; however, even if such small differences ultimately prove real, they are of questionable significance with respect to the etiology and pathogenesis of these diseases.
With regard to age, several points deserve attention. The peak for Crohn’s colitis occurred somewhat later, in the 21-to-25-year-old group. Whereas a clear secondary peak was noted in the 55-to-60-year-old group of patients with ulcerative colitis, a small secondary peak was noted for men only in the 46-to-50-year-old group with regional enteritis.
While numbers were small, no secondary peak was noted in the group with Crohn’s colitis. It is also noteworthy that the incidence of ulcerative colitis far exceeds that of Crohns disease in the very young, with increased incidences of both diseases after age 10.
Although various hypotheses have been proposed to explain the bimodal curve noted particularly for ulcerative colitis, including both vascular insufficiency and immunologic Crohns disease mechanisms, this observation has yet to be clarified.