Combined detrusor instability and stress urinary incontinence: where is the primary pathology?

Thirty-nine patients (from a total of 307 women) with clinical and urodynamic diagnosis of stress urinary incontinence had cystometric findings consistent with detrusor instability. Detailed multichannel urethrocystometry of these 39 patients revealed that urethral relaxation preceded the bladder contraction by 2-5 s. These patients were randomly allocated to either medical treatment (n = 21) by Ditropan 5 mg t.i.d. for 6 weeks prior to the surgical procedure, or to surgical treatment (n = 18) with no attempt to treat the bladder instability prior to surgery. All patients had repeat clinical and urodynamic evaluation at 3-12 months postoperatively. Six of the 39 patients (15%) still had urethral relaxation and bladder contractions on postoperative urethrocystometry. Four of these 6 patients still had stress urinary incontinence and urethral funneling. These 4 were considered surgical failures. Two of the 39 (5%) had postoperative detrusor instability in spite of good surgical results. This series suggests that in women with combined stress urinary incontinence and bladder instability, where bladder contraction is preceded by urethral relaxation, there is a more than 90% chance that bladder instability will disappear after successful operation for stress urinary incontinence.