Research Updates in Kidney and Urologic Health

NIDDK Supports Epidemiology of Interstitial Cystitis

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) has issued a request for applications (RFA) to support investigation of the epidemiology of interstitial cystitis and painful bladder syndrome (IC/PBS) in response to recommendations from the Interstitial Cystitis (IC) Epidemiology Task Force. The group—the IC Executive Committee, ad hoc participants, and National Institutes of Health (NIH) staff—met in Bethesda, MD, last October to review current investigations of IC and to plan new epidemiology investigations. The request for applications is available online.

The objectives of the research program described in this RFA are to

• develop a population sampling strategy to survey the prevalence of people with symptoms of IC/PBS
  
  
• develop diagnostic categories and methods for assessing the severity of IC/PBS symptoms
  
  
• develop questionnaires to assess IC/PBS using both current examples of symptom assessment and advice of IC/PBS experts
  
  
• conduct well-designed, population-based studies that will estimate the prevalence of people with IC/PBS symptoms and determine the characteristics of that population
  
  
• provide for clinical evaluations of a subset of symptomatic individuals and control subjects by clinicians with demonstrated IC expertise
  
  
• assess quality of life, severity of pain, and the impact of pain issues
  
  
• determine the socioeconomic impact of IC/PBS
  
  

Points of Consensus

The task force reached consensus on several points that should inform the effort to standardize the epidemiological study of IC.

IC is a symptomatic diagnosis based on the presence of three key symptoms, pain, urgency, and frequency, as well as the exclusion of a few other conditions that cause the same symptoms.

• Pain is the most consistent and disabling symptom for IC patients. Some will not use the term pain, but will instead describe a sense of pressure or discomfort. Typically, but not always, the pain is worse when the bladder is filling and is relieved as the bladder empties.
  
  
• Urgency in IC patients differs from that experienced by patients with urinary incontinence. In IC patients, the urgency is driven by pain; in patients with incontinence, it is driven by their fear of losing control.
  
  
• Not enough information is available on normal variability of urinary frequency to establish a number that can help diagnose IC.
  
  

NIDDK criteria for IC were developed to select a set of patients for clinical trials. Many patients who experienced clinicians would agree have IC do not meet these criteria, making the criteria too restrictive for epidemiologic studies. The criteria used by experienced clinicians need to be standardized for use in epidemiologic studies.

Even asking subjects whether they have ever been diagnosed with IC is not useful because they frequently confuse the term "interstitial cystitis" with "acute bacterial cystitis."

Recommendations

The task force issued the following recommendations to address the methodological issues researchers will face in this effort.

1. Use a population-based sampling strategy to identify people who have symptoms of IC/BPS. An example of this type of strategy is the one used by the Chronic Fatigue Syndrome Research Program of the Centers for Disease Control and Prevention.
   
   
2. Perform more intensive evaluation on a sample of symptomatic subjects and on control subjects.
   
   
3. Draw a sample for intensive study from a region in the United States near one or more clinical evaluation sites.
   
   
4. Consider a national strategy for telephone surveys, if cost permits.
   
   
5. Include people with early symptoms of the illness in the study. Enrollment targets should ensure an adequate number of short-term patients.
   
   
6. Limit the survey to persons with bladder symptoms, eliminating people who have vulvodynia or chronic pelvic pain.
   
   
7. Perform prospective studies to identify the risk factors for developing IC/PBS.
   
   
8. Perform a longitudinal study of symptomatic subjects and controls as resources permit. Although the case literature and the Interstitial Cystitis Database provide some valuable information on the natural history of established IC, the natural history of early symptoms is unclear.
   
   
9. Perform studies to validate the sensitivity and specificity of antiproliferative factor for diagnosis of IC. Assess the value of measuring antiproliferative factor in a sub-group of symptomatic persons to predict progression of IC and to monitor their responses to therapy.
   
   
10. Collect biosamples from subjects and perform microarray and proteomics analyses to develop other markers of IC that might contribute to an understanding of disease pathogenesis. Samples suitable for such studies should be stored in a repository, and access should be arranged for qualified investigators.
    
    

NIH Publication No. 04–4531
May 2004