Epidemiology of interstitial cystitis.

OBJECTIVES

To discuss what is currently known about the population prevalence of interstitial cystitis (IC) and demographic characteristics of IC patients.

METHODS

Changes over time in the criteria for diagnosis of IC are described. The 3 published studies of the population prevalence of IC are reviewed. Epidemiologic issues important in the design of studies of IC are cited.

RESULTS

IC is a disease of chronic voiding symptoms. There is very little reliable information published on the etiology, risk factors, or number of persons affected. The criteria used for diagnosis of IC by different investigators have been variable. In 1988, research criteria for a case definition of IC were published, to be applied for IC patients enrolled in National Institutes of Health-funded studies. Three published studies of the population prevalence of IC are available. Each study used different criteria for defining a case of IC, and none used the NIH research criteria to define a case. Prevalence estimates for IC vary significantly, from 10 cases/100,000 reported in Finland in 1975, (based on hospital record review), to 30/100,000 in the United States in 1987, (based on a mailed survey of board certified urologists), to 510 cases/100,000 in the United States in 1989, (based on participant self-report in the 1989 National Health Interview Survey). It is unclear the extent to which these estimates represent true differences in prevalence, rather than reflect the different methods used to define an IC case. Several investigators have reported demographic characteristics of the IC patients followed in their clinics. All studies of adults show a marked female predominance, with reported onset of symptoms generally in the middle years of life. Patients may experience a delay of years from the onset of symptoms to the time of definitive diagnosis. The natural history of symptoms of IC has been reported to be that of a subacute onset with a rapid peak in severity, and then a relatively constant plateau of chronic symptoms thereafter. However, many patients do experience remissions and flares in their disease symptoms.

CONCLUSIONS

Few therapies for IC have been evaluated using rigorous epidemiologic methods. Many questions remain to be answered. New studies of IC should include epidemiologic consultation at the stage of study design.