DDW 2013 Note: Getting a Clear Picture of the Average Symptom Pattern in IBS

Irritable bowel syndrome (IBS) is a disorder that is defined entirely in the formal diagnostic criteria (currently the Rome III criteria) by the symptoms of abdominal pain, diarrhea and/or constipation. All of these three symptoms are known to be intermittent in the disorder. However, because few studies have tracked the bowel symptoms of large groups of IBS sufferers carefully on a daily basis over extended periods of time, our knowledge about the typical episodic behavior of these symptoms has been poor, and surprisingly little has been known about to what degree the different bowel symptoms occur together or separately. How often do patients for example have constipation on days when they also have abdominal pain? And what proportion of their total days do they have bowel symptom episodes of any type? This kind of information has not been available in IBS.

Today I presented the results of a study by our UNC-Chapel Hill research team at Digestive Disease Week 2013 in Orlando which aims to give a better picture of the typical symptom episode pattern in IBS overall. We analyzed diary data from 124 adult IBS patients who met the Rome III diagnostic criteria for the disorder and had also been diagnosed by a doctor as having the disorder. These study participants tracked their every bowel movement (BM) for 90 days in a pocket-sized diary. They rated the consistency of each bowel movement on the Bristol Stool Scale (1-7 ratings with verbal and picture descriptors where 1-2 is considered constipation and 6-7 diarrhea: See more about the scale here) and transferred these ratings to a secure website each night, where they also rated global 24-hour abdominal pain (0-10 scale).

Since we wanted to study typical symptom activity in IBS, we did several things to try to ensure that the diary data in our study reflected as natural and typical IBS symptoms as possible:

  • We used a long diary recording period. IBS is a fluctuating disorder, so to capture a characteristic pattern of symptoms for each individual, we decided we would have to track the symptoms for months. We therefore decided on a three-month (90-day) diary recording.
  • We did not study patients who were coming to clinics or doctors for help, because those would be likely to have more active symptom episodes that were bringing them in at the present time. Instead, we advertized for patients who had been diagnosed with IBS through our University mass e-mail system, on various websites and also recruited participants who had signed up in a registry to participate in research studies for our Center. We then verified that they met Rome III criteria for IBS.
  • We only included in our analysis diary information from patients who reported no laxative or anti-diarrheal medication use in their diaries during their whole diary recording period, and who were on none of the IBS-specific medications, so we could be sure that we were seeing “natural” symptom patterns unaffected by bowel medications.

The patients who ended up included in our analysis dataset were predominantly female (89%), of an average age of 36.7 years, and were of all subtypes of IBS (38 IBS-D, 69 IBS-M, 16 IBS-C, and 1 IBS-U).

The first thing we had to do in order to be able to systematically analyze symptom episode patterns in the diaries was to define what constituted an episode for each kind of symptom. For pain episodes, this was easy – we used definitions that had already been established 1 by our colleagues in a different study, and which we found reasonable based on our data. For diarrhea and constipation episodes, however, no such episode definitions existed so we conducted systematic pattern analysis of bowel movements in all the diary datasets to come up with effective episode definitions. I will not describe those analyses here, for they are rather complicated and will be described in our forthcoming paper. But the episode definitions we ended up using for the three type of central symptoms in IBS was as follows:

  • A diarrhea episode is a series of at least 2 diarrhea BMs never separated by more than 1 non-diarrhea BM nor by a day without a BM.
  • A constipation episode is a series of at least 2 constipation BMs and/or one or more sequences of 3+ no-BM days, never separated by more than 1 non-constipation BM. Constipation episodes included non-BM days.
  • A pain episode is a series of one or more days of daily pain severity rated higher than 3 on a 0-10 scale

Then we analyzed the diary records of the 124 IBS patients to see how long, how frequent and how overlapping or separate episodes of different symptoms were.

What we found was that on average, diarrhea episodes lasted 2.1 days, constipation episodes 4.45 days for constipation, and pain episodes 3.1 days.

Diarrhea episodes were present on 16.2% of total diary days, constipation episodes on 22.5% and pain episodes on a whopping 44.6% of days. Interestingly, pain episode days co-occurred far more frequently with diarrhea episode days than with constipation episode days (70.5% vs. 39.1% overlap).

Amazingly to me, we found that IBS symptom episodes of any kind (that is, either pain or constipation or diarrhea or a combination of more than one of these) were on average present on nearly two-thirds of all days for this sample of patients (63.8% of days to be precise). We also found (which perhaps does not surprise anybody) that the higher the percentage of their total days the patients spend in IBS symptom episodes, the poorer are their their quality of life scores.

Since this is a lot of complicated information with a whole bunch of number, a picture is worth a thousand words, as the saying goes. So here is a pie chart representing the typical symptom episode activity of the IBS patients in our study. The whole circle represents all days for the average IBS patient, and the various slices of the pie show what percentage of total days different types symptom episodes are occurring.

Figure. Average Symptom Pattern in IBS (% of total days; based on 3-month diaries of 124 patients):


We are continuing to analyze these diary data to further understand symptom patterns and will soon be describing our findings in more detail than we did here at DDW today in our forthcoming paper. Of course there is a huge amount of variability between individuals in their symptom picture, so the figure above does not apply to all IBS patients. Nonetheless, I think it is useful to depict the symptom episode pattern overall across IBS subtypes as I have done here, so that one can get a better appreciation of the general nature of IBS symptom activity. For example, I was surprised to see how much of total days in the life of IBS patients symptom episodes are present, even though I have done research and clinical work with IBS for nearly 20 years. You cannot get that type of bird’s-eye summary view of what IBS looks like except through this kind of thorough symptom-tracking in a large number of individuals across a long period of time.

In summary, what we are finding is that the three defining symptoms of IBS all occur in distinct episodes rather than being randomly spread over time. Pain episodes are the most frequent type of symptom episode, roughly happening on average on 2 out of every 5 days in the life of the typical IBS patients, and these pain episodes tend to overlap with diarrhea episodes more commonly than with constipation episodes. On average, patients experience IBS symptom episodes on nearly 2/3 of all days. More frequent IBS episode days are associated with increased quality of life impairment.


Tu2070. Symptom Episode Patterns in Irritable Bowel Syndrome (IBS). Olafur S. Palsson, Jeffrey S. Baggish, William E. Whitehead. Center for Functional GI and Motility Disorders, University of North Carolina, Chapel Hill, NC and CSL Behring, King of Prussia, PA


1: Hellström PM, Saito YA, Bytzer P, Tack J, Mueller-Lissner S, Chang L. Characteristics of acute pain attacks in patients with irritable bowel syndrome meeting Rome III criteria. Am J Gastroenterol. 2011 Jul;106(7):1299-307. doi: 10.1038/ajg.2011.78. Epub 2011 Mar 29. PubMed PMID: 21448146.


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