Intrinsic sphincter deficiency: what is it and does it matter anymore?

Abstract

There was a time when intrinsic sphincter deficiency (ISD) had a definition that was clinically relevant and guided the therapeutic decision-making process. However, over time the definition has become muddied and has somewhat morphed into a vague term defined in various ways with various tests. Currently, I doubt that any two clinicians use the same definition, and ISD has become more of a euphemism than a defined disease. So how did we get here? It may be the result of some technology introduced in the mid 1990s that has been described by my colleague T. Fleming Mattox as “The single most important practice altering technology in urogynecology in our lifetime,” the tensionfree vaginal tape (TVT). The term ISD was originally coined by McGuire et al. in the urology literature from the 1980s and was used to describe a severe form of stress urinary incontinence, equating it to an earlier term “type III urinary incontinence” (reported in Blavais and Olsson [1]). In the urogynecology literature ISD was equated with a concept introduced by Sand et al. in 1987 in an article describing the “low pressure urethra” [2]. These terms were urodynamically defined as a Valsalva leak point pressure (VLPP) of less than 60 mm H2O and a maximal urethral closure pressure (MUCP) of less than 20 cm H2O respectively. The disease ISD was a poor prognostic indicator and helped clinicians identify those patients at risk of failing our “gold standard” procedure for treating stress urinary incontinence, the Burch retropubic urethropexy. Subjects with ISD were felt to be better candidates for a pubovaginal sling. This literature contributed to ISD being formally defined in an Agency for Healthcare Research and Quality (AHRQ) 1996 manual on the evaluation and treatment of urinary incontinence in adults as follows: