Anal Sphincter Electromyogram for Dysfunction of Lower Urinary Tract and Pelvic Floor

Abstract

The electromyogram (EMG) is a diagnostic tool that measures and records the electrical activity produced by skeletal muscles. The anal sphincter and urethral external sphincter are skeletal muscle in nature. There are two kinds of EMG in widespread use in the field of urodynamic investigation: surface (patch) and intramuscular (fine-wire) EMG. In our laboratory, the fine-wire electrode is introduced by aid of a needle, we called it needleguided wire electrode, or simply as wire electrode (Xu et al, 2007). Sphincter EMG studies the bioelectric potentials generated in the distal striated sphincter mechanism. Such studies are performed at two different levels of sophistication, each with distinct goals and requiring different instrumentation. The first, termed kinesiologic studies, are commonly performed in the urodynamic laboratory and simply examine sphincter activity during bladder filling and voiding. The second are neurophysiologic tests, which require considerable expertise and elaborate equipment and are designed to examine the integrity of innervation of the muscle. However, clinically the most important information obtained from sphincter EMG is whether there is coordination or discoordination between the external sphincter and the bladder. Surface patch electrodes are placed on the skin/mucosa overlying the muscle of interest and thus pick up the potentials produced by various muscles in the vicinity. Wire electrodes are preferable because they are placed directly into the muscle of interest, allowing for the detection of activity in individual motor units. EMG of the anal sphincter derived from transdermal route, being combined with simultaneous recording of uroflow rate, and bladder, abdominal pressure and then detrusor pressure (=bladder pressure–abdominal pressure) during both bladder storage and voiding phases, can give rise to a general essential data about functional states of the main elements (i.e. detrusor and sphincter) of lower urinary tract and the pelvic floor. Sphincter dysfunction, either overactive or underactive, may occur in patients with either neurogenic or non-neurogenic lower urinary tract dysfunctions (LUTD). Recently, the European Association of Urology published its guideline (2008 version) on neurogenic LUTD, which is categorized into detrusor and sphincter levels, and the location of lesions is no longer emphasized (Stohrer et al, 2009). Although several classification systems have been proposed for neurogenic LUTD, the recommendations for a functional classification for