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Interstitial cystitis versus detrusor overactivity: a comparative, randomized, controlled study of cystometry using saline and 0.3 M potassium chloride.

Philip J, Willmott S, Irwin P

Michael Heal Department of Urology, Leighton Hospital, Crewe, Cheshire, United Kingdom.

PURPOSE: We compared cystometric findings in interstitial cystitis and detrusor overactivity using 0.3 M KCl and 0.9% normal saline. MATERIALS AND METHODS: Female patients with established diagnoses of IC (7 patients according to NIDDK criteria) and urodynamically proven DO (10 patients) underwent consecutive cystometrograms using 0.9% normal saline and 0.3 M KCl, the order of which was randomized for each patient. Individual CMGs were performed by separate investigators, and patients and investigators were blinded to the order in which the solutions were used and to the results of the other CMG. The results were analyzed on a comparative basis using a 2-tailed t test for comparison of the means and a Kolmogorov-Smirnov z test was used for group comparison. A ROC curve was used to plot sensitivity to the false-positive rate. RESULTS: Irrespective of the diagnosis or the type of infusion used, the volume at FDV was slightly lower with the first CMG compared to the second (mean 76.1 vs 94.2 ml) but did not reach statistical significance (p = 0.20). However, Cmax was similar for first and second CMGs (mean 214 vs 213.2 ml, p = 0.98). Although lower with KCl, there was no significant difference in FDVs obtained with either solution (mean 78.2 vs 92.2 ml for KCl and NS, respectively, p = 0.33). However, KCl produced a significant reduction in Cmax across the whole group (mean 244.5 vs 182.7 ml, p = 0.008). This was most marked in the DO group in which there was a 23% reduction in Cmax with KCl compared to NS, while the IC group showed only a 15% reduction in mean Cmax. The ROC curve, comparing Cmax values for NS with KCl cutoff values of 15% and 30%, resulted in poor positive predictive values (51% and 66%, respectively) for comparative cystometry in distinguishing IC from DO. CONCLUSIONS: The 0.3 M KCl reduces Cmax in IC and DO, the effect being more pronounced in DO. Urothelial hyperpermeability is not specific to IC. Comparative cystometry using NS and 0.3 M KCl does not help to differentiate IC from DO.

Published 12 January 2006 in J Urol, 175(2): 566-70; discussion 570-1.
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