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TO THE EDITOR: Irritable bowel syndrome (IBS) is a common disorder characterized by persistent or recurrent abdominal pain and discomfort with altered bowel habits. It affects approximately 10%-20% of the adult population, with typical symptoms like abdominal pain, constipation, diarrhea and bloating.1,2 Although IBS is not lethal, it can reduce quality of life and increase medical costs. While the cause of IBS is still unclear, visceral hypersensitivity, immune activation, enteric neuromuscular dysfunction and dysfunction of the brain-gut axis have been suggested.3-6 Small intestinal bacterial overgrowth (SIBO) has also been proposed as an etiologic factor in IBS, but the evidence is conflicting yet.7
With great interest, I read the report by Kumar et al8 regarding the increased fasting breath hydrogen levels among patients with IBS as compared with healthy controls (HC). Kumar et al8 suggested that average fasting breath hydrogen was higher in patients with IBS as compared to HC (mean 10.1 ± 6.5 vs 5.5 ± 6.2 ppm, p < 0.001) and number of stools per week correlated with average fasting breath hydrogen excretion in patients with IBS (r = 0.26, p = 0.02). The fasting breath hydrogen level was not different between patients with diarrhea predominant IBS (D-IBS) and constipation predominant IBS (C-IBS) (either by subjective feeling or by Bristol Stool Form Scale).
Although the authors showed a clear result of different fasting breath hydrogen levels between IBS and HC, some doubt was raised because it is inconsistent with the previous results of same study group. Breath hydrogen levels were similar between IBS excluding D-IBS and HC, whatever fasting or following glucose ingestion, and the breath hydrogen levels following glucose ingestion were higher in chronic non-specific diarrhea including D-IBS than other types of IBS and HC according to the previous report.9 I wonder why the fasting breath hydrogen levels were not different between D-IBS and C-IBS in the present study. I think that the result might have changed if the authors classified the IBS subtypes by Rome III criteria.10 I also wonder about the frequency of C-IBS subtype which was higher than D-IBS, when 77 of 81 IBS patients (95.1%) complained loose stool at the onset of pain.8
In the previous studies, fasting breath hydrogen levels were not different among patients with IBS and controls, contrary to the result from the present study.11-13 Even the breath hydrogen levels following lactulose ingestion were comparable between IBS and controls.11 Although the authors suggested that this contradictory result might be related to non-comparable IBS and control group and bias in selection of IBS patients, there are still doubtful points and the result needs to be validated by larger scaled study.
The authors suggested that fasting breath hydrogen levels might correlate with diarrhea because the stool frequency per week correlated with fasting breath hydrogen level, albeit weakly.8 However, IBS patients with incomplete evacuation might visit toilet repeatedly resulting in spuriously increased stool frequency as the authors mentioned in the discussion. So, Bristol Stool Form Scale might be meaningful rather than the stool frequency for estimating the relationship between fasting breath hydrogen levels and diarrhea.14 The authors did not show the correlation between fasting breath hydrogen levels and Bristol Stool Form Scale of IBS patients. Besides, the authors hypothesized that bloating might have originated from increased hydrogen gas in IBS, but did not estimate the correlation between bloating severity and fasting breath hydrogen levels. I think that these additional data can make the present study more valuable.
Despite several limitations of the present study, it provides us with the important clues in understanding the pathophysiological mechanisms of bloating and diarrhea in IBS patients. Further large scaled studies are needed to validate the results of the present study and to clarify the role of hydrogen gas and SIBO in IBS.
Conflicts of interest: None.