Objectives.: Interstitial cystitis (IC) has been considered possibly to represent more than one disease process. If so, patients would be expected to form distinct subgroups. The degree of mononuclear inflammation on bladder biopsy can be objectively quantified and might be a useful parameter for subgroup division. The hypothesis of this study was that patients with mild versus severe inflammation would differ with regard to other clinical features of IC. Methods.: Sixteen patients who met the original National Institute of Diabetes, Digestive and Kidney Diseases criteria for IC underwent cystoscopy with bladder distention and biopsy. The degree of mononuclear inflammation on bladder biopsy was classified as mild, with less than 100 mononuclear cells/high power field (HPF), or severe (100 or more mononuclear cells/HPF or lymphoid aggregates). Associations were sought between degree of inflammation and other subjective and objective clinical features. Results.: Five patients had severe inflammation and 11 had mild inflammation. The major finding was that the patients with severe inflammation experienced better symptom relief after cystoscopy with bladder distention under anesthesia. This difference was highly significant (Fisher's exact test, p = 0.0014). For the other clinical features studied, these two groups did not differ significantly. Conclusions.: Two distinct IC patient groups were identified by bladder biopsy findings.These two groups had significantly different treatment responses. If this difference is confirmed with a larger number of patients, it would suggest that these two patient groups may have different underlying disease processes.
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