Detrusor instability. Is the bladder the cause or the effect?

Seventy-two patients had a clinical and urodynamic diagnosis of detrusor instability. All were given four weeks of anticholinergics (oxybutinin, 5 mg three times a day) and had their evaluation repeated. Forty-one patients (57%) responded favorably to the anticholinergics, and 31 (43%) did not. The 31 discontinued the anticholinergics and were placed on sympathomimetics (phenylpropanlamine, 25 mg two times a day) for another four weeks before repeating their evaluation. Based on urethrocystometry, two groups were identified: group I (n = 44) had bladder contraction that preceded any urethral pressure change, and group II (n = 28) had urethral relaxation that preceded bladder contraction. Most women in group I (38 or the 44 [86%]) responded favorably to anticholinergics. Most women in group II failed to respond to anticholinergics, while more than two-thirds of them (19 of 28 [68%]) responded favorably to sympathomimetics (P less than .001). Our results suggest that bladder contraction that precedes any urethral pressure change represents detrusor pathology as opposed to bladder contraction that follows urethral relaxation: it probably represents urethral pathology.