THE ROLE OF URINARY POTASSIUM IN THE PATHOGENESIS AND DIAGNOSIS OF INTERSTITIAL CYSTITIS

Purpose: We determined whether intravesical potassium absorption in no rmal bladders correlates with increased sensory urgency, and corrobora ted the hypothesis that mucus is important in the regulation of epithe lial permeability. We compared sensory nerve provocative ability of so dium versus potassium, and determined whether intravesical potassium s ensitivity discriminates patients with interstitial cystitis from norm al subjects and those with other sensory disorders of the bladder. Mat erials and Methods: A total of 231 patients with interstitial cystitis and 41 normal subjects underwent intravesical challenge with 40 ml. w ater and then 40 ml. of 40 mEq./100 ml. potassium chloride. Subjective responses of urgency or pain stimulation were recorded on a scale of 0 to 5. In 19 normal subjects potassium absorption was measured at bas eline, after injury of the bladder mucus with protamine, after heparin treatment to reverse mucus damage and then for a final time. These su bjects simultaneously recorded the symptoms of sensory urgency and pai n at baseline, after protamine and after heparin. Another group of nor mal volunteers underwent a challenge with sodium versus potassium to d etermine which cation was more provocative. Patients with bladder outl et obstruction secondary to benign prostatic hyperplasia (BPH), detrus or instability, and acute and chronic urinary tract infection but no c urrent infection were also evaluated for potassium sensitivity. Result s: Neither normal subjects nor patients with interstitial cystitis rea cted to water administered intravesically. There was marked sensitivit y to intravesical potassium in 75% of patients with interstitial cysti tis versus 4% of controls (p < 0.01). Only 1 patient with BPH responde d to potassium and none of the 5 with chronic urinary tract infection responded. All 4 patients (100%) with a current acute urinary tract in fection reacted positively to the potassium challenge. Of 16 patients with detrusor instability 25% responded. Normal subjects had minimal s ensitivity to potassium before (11%) and markedly increased sensitivit y after (79%) protamine treatment, and these symptoms were reversed by heparin in 42%. Potassium absorption directly correlated with symptom s (0.4, 3.0 and 1.3 mEq. before and after protamine, and after heparin reversal, respectively). In regard to sodium versus potassium provoca tion, potassium was far more provocative for causing urgency after pro tamine (10 versus 90%). Neither group underwent provocation before pro tamine. Conclusions: Chronic diffusion of urinary potassium into the b ladder interstitium may induce sensory symptoms, damage tissue and be a major toxic factor in the pathogenesis of interstitial cystitis. Int ravesical potassium sensitivity is a reliable method for detecting abn ormal epithelial permeability. It discriminates between patients with interstitial cystitis and normal subjects with intact epithelial funct ion, and it is a useful diagnostic test for interstitial cystitis. Pot assium sensitivity correlates with increased potassium absorption in n ormal subjects, and potassium is far more provocative than sodium. Pot assium sensitivity is also present in acute urinary tract infection an d occasionally detrusor instability but not in BPH or chronic urinary tract infections.