DISCUSSION
IBS is chronic functional gastrointestinal tract disorder which causes
abdominal pain and alteration to bowel habit in 10-15% of the
population, which is in keeping with the results of our study. There is
also a greater preponderance toward women, with some estimates
suggesting more than half are without a formal diagnosis. [9] Our
findings demonstrate that patients with IBS have significantly worse
faecal incontinence after primary OASIS repair. Women without IBS did
not show significant difference in faecal incontinence after primary
OASIS repair compared to controls. Uniquely we have also shown that the
presence of IBS in post caesarean section in primigravid patients – in
whom there were no sphincter injuries – also demonstrated higher faecal
incontinence scores albeit more modestly. Lastly we have shown that
persistent sphincter defects after primary OASIS repair did not
correlate to worse faecal incontinence scores. [10]
OASIS causes both short and long-term complications after childbirth
such as perineal pain, dyspareunia, faecal and urinary incontinence; in
addition to emotional and psychological effects. [11, 12] Immediate
surgical repair by experienced obstetricians or colorectal surgeons
trained in sphincter tissue recognition within 12 hours is considered
the gold standard, either using an overlapping or end-to-end technique.
[13, 14] The exact incidence of faecal incontinence after OASIS is
likely under-reported as some patients feel unable to discuss their
symptoms with a medical professional. [15]
OASIS are classified within the spectrum of perineal tears. The
internationally accepted classification of obstetric perineal trauma is
as follows [4]: first degree – laceration of vaginal epithelium or
perineal skin, second degree – involvement of perineal muscles, third
degree – disruption of <50% external sphincter (IIIa),
>50% external sphincter (IIIb), or both external and
internal sphincter (IIIc), and most severe fourth degree – disruption
of anal epithelium. Previous studies have suggested that grading of
obstetric sphincter injuries can help prognosticate quality of life and
manometry outcomes. [16, 17] The risk of sphincter defects following
vaginal delivery may be as high as 26% and up to half of these are
missed on routine physical examination immediately post-partum, however
women with IBS are at no increased risk of obstetric sphincter injury.
[10, 18]
When assessing women with different grades of sphincter defect on
ultrasound, our findings reveal no significant difference in mean Wexner
scores compared to women without sphincter defects. Roos et al [17]
report comparable rates of incontinence and sphincter defects to our
population, however they found that a combined IAS and EAS defect
resulted in worse faecal incontinence after a mean follow up of 9 weeks.
Our study used more liberal criteria to define ultrasonographic residual
sphincter defects in the absence of standardised and clinically
validated residual defect definitions. Our study confirms claims of
other studies that ultrasonographic sphincter defects may not reliably
correlate with increased severity of faecal incontinence after the
initial post-partum period [19, 20]. Our findings provide evidence
that after OASIS repair, screening for presence of IBS may be more
valuable than ultrasonography in predicting those at risk of worse
long-term faecal incontinence which could facilitate more targeted
behavioural, dietary, or pharmacological intervention.
We found that women who are unable to delay defaecation experience more
severe faecal incontinence. Faecal urgency occurs due to unexpected
contractions within the rectum and subsequent relaxation of the anal
canal. A population-based study by Bharucha et al [19] support our
findings, identifying urgency as a significant risk factor for
post-partum faecal incontinence. In a healthy rectum, intraluminal
pressure beyond 300 millilitres results in a feeling of urgency.
[21] Although not extensively studied, the effects of hormonal
changes intra- and post-partum are also believed to influence
gastrointestinal tract function in women with IBS. For example,
oestrogen influences the gut-brain axis which upregulates visceral
hypersensitivity and mucosal immune activation. [22] Manometry
reveals increased mucosal sensitivity to electrical stimulation of the
upper anal canal compared to parous women without IBS. [10] These
factors may therefore lower the threshold required for urgency to occur
and synergistically increase the risk of faecal incontinence following
OASIS repair.
A major strength of this study was the dual versatility of the
questionnaire which allowed standardisation of subjective symptoms by
calculation of a Wexner score, and also diagnosing IBS based on Rome IV
criteria. This ensured that patients who may not have a formal diagnosis
of IBS (which as stated earlier is not infrequent) were appropriately
categorised to increase accuracy of our results. An additional strength
of the study was the mean follow up interval of over two years, which
facilitated assessment of symptoms beyond the commonly studied early
post-partum period.
A limitation to the present study was the predominance of younger
patients in the control groups, as it is known that the risk of faecal
incontinence increases with age [3]. Mean Wexner scores were
significantly higher in the older Group A, but linear regression
analysis allowed control for this variable and age did not significantly
alter faecal incontinence scores in our cohort. Another limitation is
the single centre design which may be improved by future research
utilising a multi-centre design and recruiting a larger sample size.