Pain from intravesical instillation of cold saline can help clinicians distinguish among ailments
Pain elicited by the ice-water test helps differentiate painful bladder syndrome (PBS) from overactive bladder disorders, according to a new study.
The bladder-cooling reflex (uninhibited detrusor contractions evoked by the test) has been ob-served in adults with neurogenic detrusor overactivity (NDO), but the significance of pain during the test has remained uncertain. Nerve fibers expressing the cool and menthol receptor TRPM8 are increased in patients with idiopathic detrusor overactivity (IDO) or PBS and these receptors are thought to be triggers of the bladder-cooling reflex.
In a study by Gaurav Mukerji, MD, and colleagues at Imperial College London, the ice-water test was performed in 17 patients with PBS, 22 patients with IDO, and four patients with NDO. The control group included 21 patients with stress urinary incontinence. The test was performed by intravesical in-stillation of cold saline (0° to 4° C) up to a maximum of 100 mL at a rate of 50 mL/min. The saline was retained for one minute.
A positive test was defined as the presence of uninhibited detrusor contraction evoked by cold saline, associated with urgency or fluid expulsion. The test was positive in six (27%) of the 22 patients with IDO and in all four patients with NDO, and negative in all 17 patients with PBS and in the control group. The mean increase in detrusor pressure during a positive ice-water test was 44.7 cm.
No significant association between a positive ice-water test and cold sensation was observed in the su-prapubic region. Pain associated with bladder filling to capacity during urodynamics was reported by 16 patients (94%) with PBS but not by any of the control patients or those with NDO or IDO.
In the patients with PBS, the pain score was significantly higher at maximum cystoscopic capacity than at baseline. The pain during urodynamics was relieved by voiding and similar in character and distribution to the pain seen during the ice-water test.
The pain elicited by ice-water instillation in patients with PBS “suggests peripheral and/or central sensitization, evoking pain symptoms without reflex detrusor contractions,” the researchers wrote in BMC Urology (2006;6:31). “The report of pain in PBS, but not in IDO patients, may indicate periph-eral and/or central sensitization in PBS.”