PBS/IC incidence, causes: Studies offer some clues

April 1, 2007

Exactly what painful bladder syndrome/interstitial cystitis is, how many people have it, what the risk factors are, what its causes are, what its natural history is, and how it differs from other types of voiding dysfunction in men are questions still looking for answers.

Key Points

Bethesda, MD-Exactly what painful bladder syndrome/interstitial cystitis (PBS/IC) is, how many people have it, what the risk factors are, what its causes are, what its natural history is, and how it differs from other types of voiding dysfunction in men are questions still looking for answers.

Recent and ongoing epidemiologic studies discussed here at the 2006 NIDDK International Symposium: Frontiers in Painful Bladder Syndrome and Interstitial Cystitis are already bringing some answers into view.

"We need an evidence-based, symptom-specific definition that is accurate enough for epidemiologic studies," said Philip M. Hanno, MD, professor of urology at the University of Pennsylvania, Philadelphia.

Although prone to overestimation because of the symptom-based definitions and self reports, the population-based studies' close concordance suggests validity and sends a message that many more patients need to be treated.

J. Quentin Clemens, MD, assistant professor of urology at Northwestern University's Feinberg School of Medicine in Chicago, has co-authored two recent epidemiologic studies. The first, based on National Health and Nutrition Examination Survey data and self report of both symptoms and a diagnosis of IC or PBS, yielded an overall incidence of 470 per 100,000. The second, which depended on physician diagnosis of patients in the Kaiser Permanente Northwest HMO, yielded an overall incidence from 45 to 200 per 100,000 overall, depending on the definition, but with a consistent female-to-male ratio of 5 to 1. That points to PBS/IC as much more common in men than the often-cited 9-to-1 ratio implies.

Whatever the incidence, Dr. Clemens said, "there's no doubt that there's a huge difference between prevalence of symptoms and the presence of an IC diagnosis in this population."

The NIDDK-sponsored Boston Area Community Health (BACH) survey has gathered urologic symptom data from 2,300 men and 3,200 women age 30 to 79 years, African-American, Caucasian, and Hispanic. Based on the symptom definition of pain increasing with bladder filling and/or pain relieved by urination and a duration of at least 3 months, the prevalence of PBS/IC peaks at 4% in women in their 40s and at about 2.3% in men in their fifth and sixth decades, showed John McKinlay, PhD, senior vice president and chief scientist at the New England Research Institutes in Watertown, MA. There was no significant difference in prevalence among the racial and ethnic groups, and any differences are accounted for by socioeconomic status. Interestingly, the sex ratio was the lowest any epidemiologic study has found so far, with about twice as many women as men affected.

Associated conditions

These studies have also yielded information on associated conditions and quality of life that holds clues to etiology and natural history and keys to more successful clinical management. The Kaiser study showed the economic impact was high, with direct medical costs that are more than double those for controls. The BACH study showed the impact on quality of life to be much more severe than that of other major chronic diseases, such as diabetes and heart disease. Both of these studies revealed an association of PBS/IC with abuse and depression. In addition, the Kaiser study also found very high odds of endometriosis and gastrointestinal disorders in PBS/IC patients compared with controls. Clearly, the patients need therapy for more conditions than their bladder symptoms alone and more effective therapies to help bring down costs.

Population-based studies describe the incidence, prevalence, and potential risk factors with the most accurate data, "but it's very expensive data," Dr. Hanno said. In contrast, he noted, case-control studies can identify risk factors, demographic features, familial aggregation, and associated syndromes cost effectively. Enriched with new-onset cases, these will allow the basic science studies that might provide clues to the development of disease.