FEMALE UROLOGY

Comparative assessment of maximal bladder capacity, 0.9% NaCL versus 0.2 M KCL, for the diagnosis of interstitial cystitis: a prospective controlled study
Daha LK, Riedl CR, Hohlbrugger G, Knoll M, Engelhardt PF, Pflüger H
Department of Urology, Ludwig Bolzmann Institute of Urology and Andrology, Municipal Hospital Lainz, Vienna, Austria
J Urol. 2003; 170: 807-9

• Purpose: Increased urothelial permeability has been proposed as a cause of interstitial cystitis (IC). The potassium sensitivity test assesses bladder discomfort after instillation of 0.4 M KCL for identification of increased urothelial permeability. Since exposure to 0.4 M KCL may be extremely painful for patients with IC we investigated a less traumatic alternative.
• Materials and Methods: The study comprised 38 controls and 40 patients with IC. In all subjects cystometry was performed with 0.9% NaCL followed by 0.2 M KCL, and filling volume at first urge and maximum bladder capacity (Cmax) were assessed for both solutions.
• Results: Controls did not show a significant change in Cmax. KCL decreased Cmax in 37 of 40 (92%) patients with IC with a mean decrease of 30%. The examination was painless in all controls and in 33 of 40 (82%) patients with IC, and was moderately painful in 7.
• Conclusions: For demonstration of increased potassium sensitivity and diagnosis of IC, comparative assessment of Cmax is a well tolerated alternative to the 0.4 M potassium sensitivity test. Statistical evaluation of these results suggests that a decrease in Cmax greater than 30% is indicative of IC.
  
  
• Editorial Comment
  The authors evaluate the value of diagnostic testing for interstitial cystitis by comparing cystometry changes using a 0.2 M KCL instillation solution as opposed to a standard potassium sensitivity test using an instillation of 50 cc of 0.4 M KCL. The authors compared two groups of patients: 40 female patients with interstitial cystitis and 38 control patients. Interstitial cystitis patients had been diagnosed using the National Institute of Health / National Institute for Diabetes and Digestive and Kidney Diseases criteria for IC. Both the control and IC group underwent standard cystometry using 0.9% NaCL solution then drained and retested with 0.2 M KCL at a rate of 50 cc/min. At the end of this, all patients underwent a potassium sensitivity test (PST) with instillation of 50 cc 0.4 M KCL. The authors then looked at changes in maximum capacity between the cystometry utilizing normal saline and those with 0.2 M KCL compared the differences between the groups of controls and patients with interstitial cystitis. Using a cutoff of a 30% maximum capacity reduction, the test was found to have a sensitivity of 73% and a specificity of 83% to confirm the diagnosis of interstitial cystitis.
  This is a valuable article in view that it expands the horizons of testing for evaluation of interstitial cystitis. The potassium sensitivity test is more of a static subjective test as it is based on the patient’s ability to respond if there is an increase of pain or not. The urodynamics test allows the physician to observe a more quantitative change in bladder sensation and capacity secondary to the instillation of KCL solution and then deduce whether the patient has the diagnosis of IC. To truly appreciate this article, one must accept the validity of the KCL sensitivity test as truly diagnostic of interstitial cystitis. Potential difficulties may arise in the patient’s changed or altered response to a second urodynamics test in a short period of time. On the second cystometry, the patient has the potential to anticipate the various parameters and thus change the important parameters of testing. In addition, it is unclear what the effects of two cystometrograms will then have on a subsequent PST. Nevertheless, in view of the difficulty of therapy of this disease and its multi-factorial nature, any test that will help shed light upon this difficult diagnosis is of true value; the method of cystometry described in this article is one such test.

Dr. Steven P. Petrou
Associate Professor of Urology
Mayo Medical School
Jacksonville, Florida, USA