When this chapter was first written in 1990, Interstitial Cystitis (IC) had no established universally accepted definition and no widely agreed upon diagnostic criteria. Consequently, patients receiving the clinical diagnosis constituted a wide range of different phenotypes of urinary frequency, urgency or pain—a diagnosis established primarily based on symptoms—depending on the diagnostic criteria created by the individual doctor making the diagnosis.

The lack of established sensitive or specific objective symptoms or signs is evident in the NIDDK criteria published in this book in 1990. The NIDDK criteria were primarily established for selecting patients for scientific studies. Because of the desire to not exclude any subjects with predominant urgency “or” pain from potential treatment—these criteria permitted the investigator with subjectsto include a wide range of the symptom spectrum—but did not provide the clinician with a specific criterion for the diagnosis of patients.

In the NIDDK criteria PAIN or URGENCY were the two symptoms selected to be necessary for inclusion into clinical studies of IC. Important was the word “or”, indicating that patients with the symptom of urgency, but no pain were eligible to receive the diagnosis. Taking a retrospective look at the last 30 years, this definition permitted many to be diagnosed as having IC, who since the introduction of Overactive Bladder Syndrome (OAB) in 2002 [1] would be diagnosed as having idiopathic OAB. Today this is still the case in many countries in Asia, where the NIDDK criteria until very recently were the diagnostic criteria for IC [2].

This is only one example of the heterogeneity of IC patient populations of that time. The desire for broad inclusion criteria while establishing the etiology of the disease made the establishment of diagnostic criteria and therapeutic responses highly challenging and almost with certainty doomed to be a failure. Chapter 6 which provided many etiologic theories and no positive conclusions confirms this dilemma.

ESSIC introduced in 2008 Bladder Pain Syndrome (BPS) instead of IC [3] including a definition of the disease and a classification system. Due to problems with regulatory authorities, reimbursement, etc., the terminology utilized today is often BPS/IC or IC/BPS employing the ESSIC definition or another modification of this without changing the traditional definition. Nevertheless, BPS is still a heterogeneous patient group and the search for one or more unifying etiologies has still not been very successful.