A 45-year-old with stress urinary incontinence (SUI) undergoes urodynamic assessment. Which urodynamic parameter most directly quantifies the functional urethral length and sphincter mechanism, distinguishing intrinsic sphincter deficiency (ISD) from urethral hypermobility?
- A Maximum urethral closure pressure (MUCP) — ISD defined as MUCP <20 cmH₂O
- B Q-tip test angle >30° indicating urethral hypermobility
- C Post-void residual volume >100 mL
- D Valsalva leak point pressure (VLPP) — ISD defined as VLPP <60 cmH₂O ✓
Explanation
Valsalva leak point pressure (VLPP) — the intravesical pressure at which leakage occurs during Valsalva — is the urodynamic parameter distinguishing intrinsic sphincter deficiency from urethral hypermobility. VLPP <60 cmH₂O indicates ISD (sphincteric failure independent of anatomical support), VLPP 60–90 cmH₂O suggests mixed/overlapping pathology, and VLPP >90 cmH₂O indicates urethral hypermobility as the primary mechanism. Maximum urethral closure pressure (MUCP <20 cmH₂O) is an alternative urethral pressure profilometry criterion for ISD. The Q-tip test assesses urethral mobility (not sphincter function). Post-void residual does not assess sphincter mechanism.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
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