Electromyographic study of the striated urethral sphincter in type 3 stress incontinence: Evidence of myogenic-dominant damages

Objectives. To determine the electromyographic features of the striated ure thral sphincter in patients with type 3 stress incontinence (SI) due to int rinsic sphincteric deficiency (ISD), Methods. We performed electromyography (EMG) of the striated urethral sphin cter muscle and urodynamic studies in a total of 51 women, 41 female patien ts with type 3 SI and 10 women with normal urinary control (NUC). The resul ts were analyzed in both groups, and the correlation of EMC findings with t he patient characteristics and urodynamic parameters was evaluated. Results. Motor unit potentials (MUP) of SI patients showed significantly sh orter duration (P = 0.0014), lower amplitude (P = 0.0008], and larger numbe r of phases (P = 0.0022) compared with those in the NUC group. Thirty (73%) of the SI patients showed an obvious low amplitude (less than 350 muV)/sho rt duration (less than 4.5 milliseconds)/polyphasic pattern and early recru itment of interference activity with low amplitude at voluntary contraction of the striated sphincter, both indicating existence of myogenic damages. These patients showing myogenic damages had significantly lower Valsalva le ak point pressure [P = 0.002) and more leakage in the pad-weigh test (P = 0 .010) compared with the SI patients without myogenic damage findings. Conclusions. These results suggested that myogenic-dominant damages of the striated urethral sphincter may contribute to the etiology of ISD in most p atients with type 3 SI. UROLOGY 56: 946-950, 2000, (C) 2000, Elsevier Scien ce Inc.