Urethral pressure changes in women with detrusor instability. Bladder or urethral pathologic process?

One hundred and fourteen female patients had clinical and urodynamic diagnosis of detrusor instability. They all received oxybutynin chloride (Ditropan) 5 mg t.i.d. for four weeks and evaluation repeated. Sixty-six of the 114 patients (58%) responded favorably to anticholinergic treatment while 48 patients (42%) did not. Based on urethrocystometry, two groups of patients were identified: Group I consisted of 73 women with bladder contraction that preceded any change in urethral pressure. Group II consisted of 41 patients with urethral pressure drop that preceded the detrusor contraction by a few seconds. Sixty-one of the 73 women (84%) in Group I responded favorably to four weeks of anticholinergic therapy while 88 percent (36 of 41) of women in Group II did not (P less than 0.01). Our results suggest that women with bladder contraction that is preceded by urethral relaxation represent a different pathologic entity than women with "classic detrusor instability".