In 1990, very little epidemiological data was available to determine the prevalence, much less the incidence of Interstitial Cystitis. The only population based study was from the original author of this chapter, K. J. Oravisto, published in 1975 [1]. In his chapter, Oravisto summarizes some older publications which described small uncontrolled studies including patients with variable and sometimes suspect diagnoses. His landmark 1975 study was not only the first study of its kind but also the only study available to Oravisto at the time he was writing his 1990 chapter. His definition of IC included patients with frequency and pain or discomfort, abnormal biopsy and temporary relief with overdistension of the bladder. In the province of Uusimaa in southern Finland (included city of Helsinki), there were a total of 103 IC patients, 95 women and eight men. The overall prevalence in women (too few men to accurately analyze) over 20 years was 18.6 per 100,000. Over a 10 year period, 64 (61 female) patients were diagnosed with IC; an incidence rate of 1.3 per 100,000 for women over 20 years. He noted that 8% of IC patients in his series were male and when he combined all the series in the literature from 1939 to 1978, the ratio of men to women was noted to be 9.1:1. So how do these figures compare to our contemporary epidemiological studies for this enigmatic condition?

Since 1990, the definition of IC has evolved to now include patients with bladder pain syndrome (initially referred to as Painful Bladder Syndrome) and we have developed validated questionnaires with appropriate inclusion and exclusion criteria to identify, with reasonable accuracy, patients with IC/BPS. But the accuracy of epidemiological studies remains problematic, primarily because the condition is a syndrome (no physical or biochemical marker) and the diagnosis is one of exclusion (excluding confusable diseases that can cause bladder pain and storage symptoms). Since Oravisto’s original publication [1] there have been many studies attempting to determine the prevalence and incidence of IC and IC/BPS but they remain difficult to interpret and compare because some are based on unverified self report, others by physician diagnoses (with or without some type of verification) or by identification of BPS symptoms (with or without exclusion of other confusable conditions). There is no wonder then that estimates of prevalence vary widely from 4.5 per 100,000 females in Japan [2], to a questionnaire based study that suggests a figure of 20,000 per 100,000 in US women [3]. Self -report of a previous diagnosis of IC in the 1989 National Household Interview Survey estimated that for women this prevalence figure was 865 per 100,000 [4] while an estimate of IC from the third National Health and Nutrition Examination Survey (NHANES III) claimed a remarkably similar estimated prevalence of 850 per 100,000 women [5].

Estimates based on physician diagnoses range from 8 to 197 per 100,000 women [6–8]. Prospective surveys using validated criteria evaluating the prevalence of BPS like symptoms, rather than diagnoses, produce much higher estimates, ranging from 0.8% to 2.7% [9], a range collaborated by other less sensitive older surveys [10]. It is noted, however, that such estimates of IC/BPS prevalence drop drastically if the subjects are examined by urologists to confirm the diagnosis [11, 12]. Using different definitions of IC/BPS also changes the prevalence estimates from 3300 to 11,200 per 100,000 women based on which of three definitions are used [13]. Culture may also play a role, since the estimates vary between the USA (studies described), Europe [14] South Korea [15], China [16] and Japan [2]. The most comprehensive and probably most accurate estimation of the prevalence of BPS symptoms was 2700–6500 per 100,000 based on the sensitivity of the two validated case definitions to identify IC/BPS in 131,691 adult females [17]. Based on the information from epidemiological studies published since Oravisto’s chapter in 1990, a reasonable prevalence estimation for patients diagnosed with BPS would be about 100–200 per 100,000 women with a male prevalence of 10–20% of the female estimate. The prevalence of women and men with symptoms suggestive of BPS could be as much as ten to even 100 times more.