I went back and looked at some literature again just to make sure I didn't miss anything, but from what you describe in your first post, it is not the traditional presentation or cause of IBS, one set of diagnostic criteria for IBS are actually as follows:
Rome II criteria said:
* abdominal discomfort or pain for at least 12 weeks (not necessarily consecutive) in preceding 12 months
* abdominal discomfort or pain has 2 of the 3 following features
o relieved with defecation
o onset associated with change in stool frequency
o onset associated with change in stool form (appearance)
* supportive symptoms
o fewer than 3 bowel movements per week
o more than 3 bowel movements per day
o hard or lumpy stools
I also looked at some other sources about the suspected pathophysiology and some of the suspected causes and found the following:
-Neurologic or muscular hypersensitivity in the colon causing a motility disorder
- changes in colonic muscle nerve signals
- Increased gas production in colon (especially H)
- Indiciations of increased sensitivity to visceral (think organs/tissue such as the heart, lungs, colon, stomach, etc) stimulation
- bacterial overgrowth in the small intestine
Also a likely risk factor is a recent history of acute infectious gastroenteritis
Two other possible risk factors are:
- aerophagia - poorly fitted dentures, post-nasal drip, hiatal hernia
- antibiotic use associated with functional bowel symptoms over subsequent 4 months
So probably more then you needed to know, but where I am going with this is that IBS is generally a diagnosis of exclusion, there are a number of organic causes of many bowel disorders that should be examined first. In the case you described, sure, that could be a symptom (though not a cause) of IBS, however, there are a number of other likely diagnosis especially in populations at a lower risk of IBS that should be examined first.
As far as constipation being constipation... it gets complicated, and there are a number of different causes of constipation and the exact presentation has different clinical implications... for example constipation in a kid can mean something completely different then constipation in an adult, and the cause might also be unrelated, but then we get into a lot more complex anatomy and physio and such then we need here
