ABSTRACT
AIM: Pudendal nerve terminal motor latency (PNTML) assesses distal innervation of the external anal sphincter (EAS) but it is insensitive to early nerve damage. We propose to extend the assessment of PNTML to the measurement of the compound muscle action potential (CMAP) of the EAS to understand its progressive denervation. METHOD: Ninety women with faecal incontinence were prospectively examined and compared with 36 asymptomatic women who acted as controls. PNTML was performed bilaterally and the muscle response analysed for CMAP to include amplitude, area and duration. Anorectal manometry was measured by a station-pull technique using a water-filled microballoon. spss version 11.5 was used for statistical analysis. RESULTS: In asymptomatic women the CMAP on the left side was greater in nulliparous (n = 7) than parous (n = 27, P < 0.05) individuals. There was a positive correlation with maximum squeeze pressure and area on the left side (P < 0.05, r = 0.397). In women with faecal incontinence, CMAP on the left side had a negative correlation with age (n = 75, P < 0.05), there was no correlation with parity or anorectal manometry. Nulliparous asymptomatic women had a greater CMAP (P < 0.05) on the left side than asymptomatic parous women and parous women with faecal incontinence. Right-side measurements were not conclusive. CONCLUSION: Compound muscle action potential demonstrated progressive denervation with age in women with faecal incontinence but did not reliably identify early signs of denervation in asymptomatic women. The area on the left side related to muscle function in asymptomatic women but not in women with faecal incontinence. CMAP can distinguish between parous women with faecal incontinence and nulliparous asymptomatic women but is not a useful test of function of the EAS.
Subject(s)
Action Potentials , Anal Canal/innervation , Anal Canal/physiopathology , Fecal Incontinence/physiopathology , Pudendal Nerve/physiopathology , Adult , Age Factors , Aged , Aged, 80 and over , Case-Control Studies , Female , Humans , Manometry , Middle Aged , Parity/physiology , Prospective Studies , Young AdultABSTRACT
AIM: Studies of skeletal muscle show that fatigue rate corresponds to the proportion of fast-twitch and slow-twitch fibres that are present in the muscle. Limited work has been done on the fatigue rate of the external anal sphincter. We have prospectively studied fatigability of the external anal sphincter in women with faecal incontinence and women with normal bowel control. METHOD: Anorectal manometry was measured by a station-pull technique using a water-filled microballoon. Fatigue rate was calculated from anal pressure measurements taken every 0.1 s over a 20-s squeeze. RESULTS: Women with faecal incontinence (n=88, median -12 cmH(2) O/min) were less susceptible to fatigue than women with normal bowel control (n=36, median -43 cmH(2) O/min) (P<0.01). The external anal sphincter was less susceptible to fatigue with increasing age (P<0.01, r=0.499). In women with normal bowel control and in women with faecal incontinence fatigue rate was negatively correlated with maximum squeeze pressure (P<0.01, r=-0.287; P<0.01, r=-0.579). CONCLUSION: The external anal sphincter was less susceptible to fatigue with increasing age. Women with faecal incontinence have a weaker but more fatigue-resistant external anal sphincter. This might correspond to a higher proportion of slow-twitch muscle fibres. Histological studies are needed to examine this hypothesis.
