The after‐contraction: a true detrusor contraction or a late dyssynergic urethral sphincter contraction?

Objective  To evaluate the mechanism and significance of the after‐contraction, recorded in bladder pressure by urodynamics, at the end of micturition. Patients and methods  The urodynamic recordings showing an after‐contraction of the detrusor in 65 patients of all ages and with a variety of pathologies were re‐examined. Special attention was directed to the anal or urethral sphincter needle electromyographic activity and to the monitored urethral pressure, to determine any relationships with the patterns of detrusor pressure. Results  An after‐contraction was noted in 61 patients with detrusor instability and in 11 with urethral instability. In 59 patients it was evident that the after‐contraction, i.e. a renewed increase in detrusor pressure during the declining contraction, correlated with a sphincter contraction preceding it by a fraction of a second. Similar increases in detrusor pressure were apparent in patients with detrusor‐sphincter dyssynergia throughout voiding. In six patients the relationship was less clear mainly because there were artefacts in the curves. Conclusion  The after‐contraction arises by a sudden stopping of the outflow of urine, provoked by a sphincter contraction. This may occur by involuntary dyssynergia or by an early voluntary interruption of the voiding stream. The ‘milk back’ of urine from the proximal urethra to the bladder and the inhibited detrusor contraction (if the perineal contraction is prolonged) may cause some postvoid residual urine. It occurs mainly in the presence of detrusor and/or urethral instability.