AIMS OF THE STUDY
Intrinsic Sphincter Deficiency (ISD) causes incontinence through urethral and periurethral tissue abnormalities. It is usually associated with high grade incontinence and poor prognosis. Bladder neck hypermobility can coexist with ISD in women with GSI. Although subjective parameters such as history and physical examination are essential for diagnosing urethral dysfunction, urologists and gynecologists (1-2-3) are searching for an objective test to quantify urethral sphincter function and to diagnose ISD. This study compares the MUCP and the VLPP with grade of incontinence, age, previous urogynecologic surgery and/or hysterectomy and Urethral functional length in an attempt to see if the VLPP and/or the MUCP identify patients with ISD.

METHODS
We recruited 166 consecutive patients attending our urogynecologic center with urodynamically demonstrated Genuine Stress Incontinence. Each patient provided a standard urogynecologic history, and underwent physical examination and full urodynamic testing. The VLPP and the MUCP were determined with 200 ml bladder volume, using an infusion pump and an 8 Fr catheter. The VLPP was obtained during Valsalva maneuver. A MUCP £30 cm H20 and a VLPP £ 60 cm H20 were chosen as cut?off values. Severity of incontinence was subjective (SEAPI?QMN classification). The Kruskal-Wallis and the Chi square tests were used for statistical analysis. Accuracy was calculated from 2 x 2 tables using standard formulas.

RESULTS
Table 1 demonstrates that accuracy, in terms of grade of incontinence, is slightly better with the VLPP than with the MUCP. Table 2 shows incontinence is more severe and the incidence of poor prognostic factors is increased in patients with one or two abnormalities.

TABLE 1  Accuracy of the VLPP                  TABLE 2  Poor prognostic factors, VLPP and MUCP

and the MUCP                     § median and interquartile range in brackets

                                 ° Kruskal–Wallis  test ^F Chi square test

CONCLUSIONS
ISD, as described by the AHCPR, is a concept rather than a real diagnosis and, above all, does not indicate the method of diagnosis. Some authors have associated ISD with low urethral pressure and others with a low leak point pressure. On the basis of our experience, because the results of the two urodynamic tests do not overlap and do not identify the same population, we can hypothesize that ISD has a multifactorial genesis and that a low MUCP or a low VLPP detects a different ISD pathogenetic mechanism.

References
1. McGuire, E. J: Urodynamic findings in patients after failure of stress incontinence operations. Prog. Clin. Biol. Res., 78:
2. 1981 2. Sand PK, Bowen LW, Panganiban P, Ostergard DR: The low pressure urethra as a factor in failed retropubic urethropexy. Obstet Gynecol., 69:399. 1987
3. MeGuire EJ, Fitzpatrick CC, Wan J, Bloorn D, Sanvordenker J, Ritchey M Gormley EA: Clinical assessment of urethral sphincter function. J Urol., 150: 1452. 1993