Our study has shown for the first time that in contrast with healthy females,3
rectal sensitivity increases at the time of menses compared with all other phases of the menstrual cycle in female patients with IBS. Menses is also associated with a significant worsening of IBS symptomatology, which is in accordance with previous studies.8–11
Both abdominal pain and bloating were worse and bowel habits more frequent during menstruation. In addition, stool consistency was firmer during the luteal phase. Similar observations have been made in other studies8–11
although one study reported no change in stool form or frequency with the menstrual cycle.10
Furthermore, although general well being was reduced at menses, anxiety and depression remained unaltered throughout the menstrual cycle. This latter observation is in agreement with previous studies which have shown that psychological traits (including anxiety and depression) are not associated with perimenstrual bowel related symptoms.9,10,20
Whether perimenstrual related symptoms may be associated with more subtle changes in mood and/or tension cannot be determined from this study but it might be expected that if gross changes in psychopathology are not associated with perimenstrual bowel related symptoms then more subtle changes in psychopathology are unlikely to be associated with these symptoms.
In contrast with our previous findings in healthy women,3
rectal sensitivity at the time of menses was significantly increased with respect to all other phases of the menstrual cycle in females with IBS. This increase in rectal sensitivity did not correlate with the severity of any of the IBS symptoms. It has been shown that IBS patients can have altered visceral sensitivity throughout the gastrointestinal tract14,21,22
and it is therefore possible that menses was associated with changes in sensitivity elsewhere in the gut which may be more closely correlated with IBS symptomatology. Furthermore, the increase in rectal sensitivity seen at menses does not appear to be related to changes in rectal compliance (change in dV/dP configuration or slope of curve) or wall tension (change in Cstat
without change in Cdyn
Previous studies have suggested that hard stools during the luteal phase of the menstrual cycle may be partly attributed to high levels of progesterone and oestradiol at that time,2,4
and that diarrhoea reported at menses is related to prostaglandin production,23
possibly by inhibiting transepithelial ion transport in the small intestine.24
As an acute episode of diarrhoea induced by ingestion of an osmotic laxative is associated with an increase in rectal sensitivity in women (but not men),25
and IBS patients seem to be more susceptible to sensitising events,14–18
this may be the mechanism of the increased rectal sensitivity seen in IBS patients at menses. Alternatively, prostaglandins have been shown to induce afferent nerve sensitisation,26,27
and as the gut of IBS patients may already be hypersensitive, prostaglandin release may be enough to trigger a further increase in this sensitivity. Another possibility is that we are detecting changes in vigilance during the menstrual cycle. We believe that this is unlikely as previous studies have shown that exacerbation of gastrointestinal symptoms at menses is not related to changes in psychopathology.9,10
This is also supported by our observations that neither anxiety nor depression changed with the menstrual cycle.
Finally, no explicit statistical adjustments were made for the multiple comparisons performed in these studies but the relatively high proportion of significant results obtained probably excludes the possibility that these were obtained by chance. Furthermore, the use of a more conservative alpha level of 0.01 would not materially affect the results.
In conclusion, women with IBS appear to be predisposed to fluctuations in visceral sensitivity associated with the menstrual cycle. Understanding the pathogenesis behind these changes should help to unravel some of the mechanisms of visceral sensitisation.